UNITED STATES SECURITIES AND EXCHANGE COMMISSION

Washington, D. C. 20549

FORM 10-Q

þ		QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the quarterly period ended March 31, 2007

o		TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

For the transition period from                      to                     

Commission File Number 000-51329

XenoPort, Inc.

Delaware		94-3330837
(State or other Jurisdiction of		(IRS Employer
Incorporation or Organization)		Identification No.)

3410 Central Expressway, Santa Clara, California 95051
(Address of principal executive offices)           (Zip Code)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes þ No o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, or a non-accelerated filer. See definition of “accelerated filer” and “large accelerated filer” in Rule 12b-2 of the Exchange Act. (Check one):

Large accelerated filer o                      Accelerated filer þ                     Non-accelerated filer o

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes o No þ

Total number of shares of common stock outstanding as of April 13, 2007: 24,797,684.

 

 

XENOPORT, INC.

TABLE OF CONTENTS

		Page
PART I. FINANCIAL INFORMATION
Item 1. Unaudited Financial Statements			3
Balance Sheets as of March 31, 2007 and December 31, 2006			3
Statements of Operations for the Three Months Ended March 31, 2007 and 2006			4
Statements of Cash Flows for the Three Months Ended March 31, 2007 and 2006			5
Notes to Financial Statements			6
Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations			10
Item 3. Quantitative and Qualitative Disclosures about Market Risk			17
Item 4. Controls and Procedures			17
PART II. OTHER INFORMATION
Item 1. Legal Proceedings			17
Item 1A. Risk Factors			17
Item 2. Unregistered Sales of Equity Securities and Use of Proceeds			37
Item 3. Defaults Upon Senior Securities			38
Item 4. Submission of Matters to a Vote of Security Holders			38
Item 5. Other Information			38
Item 6. Exhibits			38
SIGNATURES			39
EXHIBIT 10.29
EXHIBIT 10.29.1
EXHIBIT 31.1
EXHIBIT 31.2
EXHIBIT 32.1

PART I. FINANCIAL INFORMATION

Item 1. Unaudited Financial Statements

XENOPORT, INC.

		March 31,				December 31,
		2007				2006
		(In thousands)
Current assets:
Cash and cash equivalents		$	58,452			$	14,857
Short-term investments			112,984				103,997
Accounts receivable			2,523				2,796
Other current assets			2,078				1,332
Total current assets			176,037				122,982
Property and equipment, net			3,746				3,532
Restricted investments			1,720				1,699
Employee notes receivable and other assets			451				452
Total assets		$	181,954			$	128,665
Current liabilities:
Accounts payable		$	582			$	144
Accrued compensation			2,265				2,928
Accrued preclinical and clinical costs			9,808				13,430
Other accrued liabilities			1,508				1,737
Deferred revenue			61,264				2,424
Current portion of equipment financing obligations			403				500
Current portion of liability for early exercise of employee stock options			257				292
Total current liabilities			76,087				21,455
Deferred revenue			21,465				21,843
Deferred rent and other			1,638				1,696
Noncurrent portion of equipment financing obligations			121				181
Noncurrent portion of liability for early exercise of employee stock options			130				205
Commitments
Stockholders’ equity:
Common stock, $0.001 par value; 60,000 and 60,000 shares authorized; 24,645 and 24,517 shares issued and outstanding at March 31, 2007 and December 31, 2006, respectively			25				24
Additional paid-in capital			290,063				287,513
Notes receivable from stockholders			(8	)			(33	)
Accumulated other comprehensive income			38				37
Accumulated deficit			(207,605	)			(204,256	)
Total stockholders’ equity			82,513				83,285
Total liabilities and stockholders’ equity		$	181,954			$	128,665

The accompanying notes are an integral part of these interim financial statements.

XENOPORT, INC.

		Three Months
		Ended March 31,
		2007				2006
		(In thousands, except per
		share amounts)
Revenues:
Collaboration revenue		$	16,539			$	1,288
Total revenues			16,539				1,288
Operating expenses:
Research and development			17,089				13,746
General and administrative			4,403				3,406
Total operating expenses			21,492				17,152
Loss from operations			(4,953	)			(15,864	)
Interest income			1,657				937
Interest and other expense			(53	)			(51	)
Net loss		$	(3,349	)		$	(14,978	)
Basic and diluted net loss per share		$	(0.14	)		$	(0.77	)
Shares used to compute basic and diluted net loss per share			24,567				19,516

The accompanying notes are an integral part of these interim financial statements.

XENOPORT, INC.

		Three Months
		Ended March 31,
		2007				2006
		(In thousands)
Operating activities
Net loss		$	(3,349	)		$	(14,978	)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation			332				441
Amortization (accretion) of investment premiums and discounts, net			(1,062	)			137
Stock-based compensation expense — employees			2,120				1,104
Stock-based compensation expense — consultants			7				87
Change in assets and liabilities:
Accounts receivable			273				(10,000	)
Other current assets			(746	)			173
Deposits and other assets			1				3
Accounts payable			438				(2,520	)
Accrued compensation			(663	)			158
Accrued preclinical and clinical costs			(3,622	)			3,102
Other accrued liabilities			(229	)			96
Deferred revenue			58,462				8,712
Deferred rent and other			(58	)			73
Net cash provided by (used in) operating activities			51,904				(13,412	)
Investing activities
Purchases of investments			(67,964	)			(4,570	)
Proceeds from maturities of investments			60,040				15,000
Change in restricted investments			(21	)			(27	)
Purchases of property and equipment			(546	)			(218	)
Net cash provided by (used in) investing activities			(8,491	)			10,185
Financing activities
Proceeds from issuance of common stock and exercise of stock options and warrants			345				102
Repurchases of common stock			(31	)			(2	)
Proceeds from repayment of promissory notes from a stockholder			25				—
Payments on capital leases and equipment financing obligations			(157	)			(178	)
Net cash provided by (used in) financing activities			182				(78	)
Net increase (decrease) in cash and cash equivalents			43,595				(3,305	)
Cash and cash equivalents at beginning of period			14,857				22,088
Cash and cash equivalents at end of period		$	58,452			$	18,783
Supplemental schedule of noncash investing and financing activities
Vesting of common stock from early exercises of stock options		$	110			$	199

The accompanying notes are an integral part of these interim financial statements.

XENOPORT, INC.

1. Organization and Summary of Significant Accounting Policies

     Nature of Operations

     XenoPort, Inc. (the Company) was incorporated in the state of Delaware on May 19, 1999. The Company is a biopharmaceutical company focused on developing a portfolio of internally discovered product candidates that utilize the body’s natural nutrient transporter mechanisms to improve the therapeutic benefits of drugs. Its facilities are located in Santa Clara, California.

     In February 2007, the Company entered into an exclusive collaboration with Glaxo Group Limited (GSK) to develop and commercialize XP13512 worldwide, excluding Japan, Korea, the Philippines, Indonesia, Thailand and Taiwan (collectively referred to as the Astellas territory). See Note 2.

     Basis of Preparation

     The accompanying financial statements as of March 31, 2007 and for the three months ended March 31, 2007 and 2006 are unaudited. These unaudited financial statements have been prepared on the same basis as the annual financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments, necessary to present fairly the Company’s financial position as of March 31, 2007 and results of operations for the three months ended March 31, 2007 and 2006 and cash flows for the three months ended March 31, 2007 and 2006. The preparation of financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual results could differ from these estimates. The results of operations for the three months ended March 31, 2007 are not necessarily indicative of the results to be expected for the year ending December 31, 2007 or for any other interim period or any other future year. For more complete financial information, these financial statements, and the notes hereto, should be read in conjunction with the audited financial statements for the year ended December 31, 2006 included in the Company’s annual report on Form 10-K.

     Revenue Recognition

     Revenue arrangements are accounted for in accordance with the provisions of Securities and Exchange Commission, or SEC, Staff Accounting Bulletin, or SAB, No. 104, Revenue Recognition, and Emerging Issues Task Force, or EITF, No. 00-21, Revenue Arrangements with Multiple Deliverables. A variety of factors are considered in determining the appropriate method of revenue recognition under these arrangements, such as whether the various elements can be considered separate units of accounting, whether there is objective and reliable evidence of fair value for these elements and whether there is a separate earnings process associated with a particular element of an agreement. Specifically, the Company accounts for each of these typical elements as follows:

	•		Up-front, licensing-type fees. Up-front, licensing-type payments are assessed to determine whether or not the licensee is able to obtain any stand-alone value from the license. Where this is not the case, the Company does not consider the license deliverable to be a separate unit of accounting and the revenue is deferred with revenue recognition for the license fee being assessed in conjunction with the other deliverables that constitute the combined unit of accounting.
	•		Milestones. Milestones are assessed on an individual basis and revenue recognized from these milestones when earned, as evidenced by acknowledgment from collaborators, provided that (i) the milestone event is substantive and its achievability was not reasonably assured at the inception of the agreement, (ii) the milestone represents the culmination of, or progress towards the culmination of, an earnings process and (iii) the milestone payment is non-refundable. Where separate milestones do not meet these criteria, the Company typically defaults to a performance-based model, with revenue recognition following delivery of effort as compared to an estimate of total expected effort. Milestones that are received after all substantive deliverables have occurred are considered to be bonus payments and are recognized upon receipt of the cash, assuming all of the other revenue recognition criteria are met.

	•		Collaborative research payments. Generally, the payments received are based on a contractual cost per full-time equivalent employee working on the project, and recognized as the services are performed over the related funding periods for each agreement.
	•		Grant revenues. Grant revenues are recognized as research is performed.
	•		Combined units of accounting. Where there are multiple deliverables combined as a single unit of accounting, revenues are deferred and recognized over the longest period over which the Company remains obligated to perform services or deliver product. The specific methodology for the recognition of the revenue (e.g., straight-line or according to specific performance criteria) is determined on a case-by-case basis according to the facts and circumstances applicable to a given contract.

     Payments received in excess of revenues recognized are recorded as deferred revenue until such time as the revenue recognition criteria have been met.

     The Company’s collaboration agreements also include potential payments for commercial product supply and product royalties. To date, no revenues have been received from either of these sources.

     Clinical Trials

     The Company accrues and expenses the costs for clinical trial activities performed by third parties based upon estimates of the percentage of work completed over the life of the individual study in accordance with agreements established with contract research organizations and clinical trial sites. The Company determines the estimates through discussions with internal clinical personnel and external service providers as to progress or stage of completion of trials or services and the agreed upon fee to be paid for such services. Costs of setting up clinical trial sites for participation in the trials are expensed immediately as research and development expenses. Clinical trial site costs related to patient enrollment are accrued as patients are entered into the trial and reduced by any initial payment made to the clinical trial site when the first patient is enrolled.

     Income Tax Expense

     Effective January 1, 2007, the Company adopted the provisions of Financial Accounting Standard Board, Financial Interpretation No. 48, Accounting for Uncertainty in Income Taxes — an interpretation of FASB Statement No. 109 (FIN 48). FIN 48 specifies how tax benefits for uncertain tax positions are to be recognized, measured and derecognized in financial statements; requires certain disclosures of uncertain tax matters; specifies how reserves for uncertain tax positions should be classified on the balance sheet; and provides transition and interim-period guidance, among other provisions.

     At the date of adoption of FIN 48, the Company had no unrecognized tax benefits and expected no significant changes in unrecognized tax benefits in the next 12 months.

     The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of income tax expense. To date, there have been no interest or penalties charged to the Company in relation to the underpayment of income taxes.

2. Collaboration Revenue

     In December 2005, the Company entered into a license agreement with Astellas Pharma Inc. for exclusive rights in Japan and five other Asian countries to develop and commercialize XP13512, the Company’s lead product candidate. Under the terms of the agreement, Astellas was granted exclusive rights to develop and commercialize XP13512 in the Astellas territory. The Company received an initial license payment of $25,000,000 in December 2005, which has been deferred and is being recognized on a straight-line basis over a period that approximates the expected patent life of XP13512. In April 2006, the Company received a milestone payment of $10,000,000 upon initiation of the Company’s first Phase 3 clinical trial of XP13512 in restless leg syndrome, or RLS, patients in the United States that is being recognized on a straight-line basis over the period of the Phase 3 clinical trial. In addition, the Company is eligible to receive potential clinical and regulatory milestone payments totaling up to $50,000,000 and is entitled to receive percentage-based royalties on any sales of XP13512 in the Astellas territory. The agreement also requires Astellas to source all product from the Company under a specified supply agreement. In the three months ended March 31, 2007, the Company recognized revenue of $1,288,000, representing amortization of the up-front license payment and first milestone payment under this arrangement. At March 31, 2007, $22,980,000 of revenue was deferred under this arrangement, of which $1,515,000 was classified within current liabilities and the remaining $21,465,000 was recorded as a noncurrent liability.

     In February 2007, the Company entered into an exclusive collaboration with GSK to develop and commercialize XP13512 worldwide, excluding the Astellas territory. In March 2007, GSK made an up-front, non-refundable license payment of $75,000,000. In addition, GSK has agreed to make additional payments of up to $275,000,000 upon the achievement of pre-commercialization milestones and up to $290,000,000 upon the achievement of specified sales levels. Under the terms of the agreement, GSK will also be responsible for all future development costs, with the exception of specified development costs that the Company will assume in connection with the development of XP13512 for RLS in the United States. The Company is entitled to receive royalties based upon a percentage of sales of XP13512 in the GSK territory for a specified period of time, unless the Company elects the option to co-promote XP13512 in the United States. In the event that the co-promotion option is elected for XP13512, the Company would share marketing and commercialization costs and would be entitled to a share of operating profits from sales of XP13512 in the United States for so long as XP13512 is sold, as well as payments on details the Company performs in the United States on Requip CR and Requip XL 24-Hour, GSK’s development-stage product candidates for RLS and Parkinson’s disease, respectively. Subject to FDA approval of the new drug application, or NDA, for XP13512, the Company would co-promote XP13512 in the United States to those same prescribers. The Company has concluded that the up-front license payment does not have value to GSK on a stand-alone basis without the benefit of the specified development activities that the Company will perform in connection with XP13512 and that $65,000,000 of milestones payable for clinical trial and pre-clinical activities were either not sufficiently substantive or not sufficiently at risk to be accounted for using the ‘when-earned’ model and, accordingly, these milestones and the up-front payment were combined into a separate unit of accounting that is being recognized over the best estimate of the development period to commercialization of the product during which time delivery of substantially all of the efforts required for the completion of the Company’s contractual responsibilities under the GSK agreement is expected to occur. In the three months ended March 31, 2007, the Company recognized revenue of $15,251,000 under this agreement. At March 31, 2007, $59,749,000 of revenue was deferred under this agreement and was classified within current liabilities.

3. Net Loss Per Share

     Basic net loss per share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period less the weighted-average unvested common shares subject to repurchase, without consideration for potential common shares. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares outstanding for the period less the weighted-average unvested common shares subject to repurchase and dilutive potential common shares for the period determined using the treasury-stock method. For purposes of this calculation, preferred stock, options to purchase stock and warrants are considered to be potential common shares and are only included in the calculation of diluted loss per share when their effect is dilutive.

		Three Months
		Ended March 31,
		2007				2006
		(in thousands)
Numerator:
Net loss		$	(3,349	)		$	(14,978	)
Denominator:
Weighted-average common shares outstanding			24,733				19,870
Less: Weighted-average unvested common shares subject to repurchase			(166	)			(354	)
Denominator for basic and diluted net loss per share			24,567				19,516
Basic and diluted net loss per share		$	(0.14	)		$	(0.77	)
Historical outstanding dilutive securities not included in diluted net loss per share calculation
Restricted stock units and options to purchase common stock			2,810				2,031
Warrants outstanding			33				39
			2,843				2,070

4. Comprehensive Loss

     The Company displays comprehensive loss and its components as part of the annual statement of stockholders’ equity. Comprehensive loss is comprised of net loss and unrealized gains and losses on available-for-sale securities. Total comprehensive loss was as follows:

		Three Months
		Ended March 31,
		2007				2006
		(in thousands)
Net loss			(3,349	)			(14,978	)
Change in unrealized gain (loss) on available-for-sale securities			1				13
		$	(3,348	)		$	(14,965	)

5. Cash and Cash Equivalents, Short-Term Investments and Restricted Investments

     The following are summaries of cash and cash equivalents, short-term investments and restricted investments (in thousands):

						Gross
						Unrealized
						Gains				Estimated
		Cost				(Losses)				Fair Value
As of March 31, 2007:
Cash		$	1,082			$	—			$	1,082
Money market funds			52,122				—				52,122
Corporate debt securities			118,194				38				118,232
Certificate of deposit			1,720				—				1,720
		$	173,118			$	38			$	173,156
Reported as:
Cash and cash equivalents										$	58,452
Short-term investments											112,984
Restricted investments											1,720
										$	173,156

						Gross
						Unrealized
						Gains				Estimated
		Cost				(Losses)				Fair Value
As of December 31, 2006:
Cash		$	3,048			$	—			$	3,048
Money market funds			11,809				—				11,809
Corporate debt securities			103,960				37				103,997
Certificate of deposit			1,699				—				1,699
		$	120,516			$	37			$	120,553
Reported as:
Cash and cash equivalents										$	14,857
Short-term investments											103,997
Restricted investments											1,699
										$	120,553

     At March 31, 2007 and December 31, 2006, the contractual maturities of investments held were less than one year. There were no gross realized gains or losses from sales or maturities of securities in the periods presented.

6. Stock-Based Compensation

     Details of the Company’s non-cash, stock-based compensation are as follows:

		Three Months
		Ended March 31
		2007				2006
		(in thousands)
Research and development		$	1,269			$	574
General and administrative			851				530
		$	2,120			$	1,104

     In January 2007, the Company’s board of directors approved the use of grants of restricted stock units to employees under the terms of the 2005 Equity Incentive Plan (2005 Plan) as part of the Company’s long-term incentive compensation program. Restricted stock units have no exercise price, are valued using the closing market price on the date of grant and vest as determined by the board of directors, typically in annual tranches over a three-year period at the rate of 25% at the end of each of the first and second years and 50% at the end of the third year. Restricted stock units granted under the 2005 Plan expire no more than ten years after the date of grant.

     During the three months ended March 31, 2007, the Company granted restricted stock units and options to purchase common stock covering 765,165 shares that had a total fair value of $11,827,000 that will be recognized over the weighted average-period of 3.7 years.

7. Subsequent Events

     In April 2007, the Company satisfied the criteria to receive $10,000,000 and $5,000,000 in milestone payments under the GSK and Astellas agreements, respectively, and expects to receive these milestone payments in May 2007.

Item 2. Management’s Discussion and Analysis of Financial Condition and Results of Operations

     This Quarterly Report on Form 10-Q contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, which are subject to the “safe harbor” created by those sections. Forward-looking statements are based on our management’s beliefs and assumptions and on information currently available to our management. In some cases, you can identify forward-looking statements by terms such as “may,” “will,” “should,” “could,” “would,” “expect,” “plan,” “anticipate,” “believe,” “estimate,” “project,” “predict,” “potential” and similar expressions intended to identify forward-looking statements. These statements involve known and unknown risks, uncertainties and other factors, which may cause our actual results, performance, time frames or achievements to be materially different from any future results, performance, time frames or achievements expressed or implied by the forward-looking statements. We discuss many of these risks, uncertainties and other factors in this Quarterly Report on Form 10-Q in greater detail under the heading “Risk Factors.” Given these risks, uncertainties and other factors, you should not place undue reliance on these forward-looking statements. Also, these forward-looking statements represent our estimates and assumptions only as of the date of this filing. You should read this Quarterly Report on Form 10-Q completely and with the understanding that our actual future results may be materially different from what we expect. We hereby qualify our forward-looking statements by these cautionary statements. Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to update the reasons actual results could differ materially from those anticipated in these forward-looking statements, even if new information becomes available in the future.

Overview

     We are a biopharmaceutical company focused on developing a portfolio of internally discovered product candidates that utilize the body’s natural nutrient transporter mechanisms to improve the therapeutic benefits of drugs. Our most advanced product candidate is currently being evaluated in a Phase 3 clinical program for the treatment of restless legs syndrome, or RLS. This product candidate has also successfully completed a Phase 2a clinical trial for the management of post-herpetic neuralgia, or PHN. Our second product candidate has generated positive data in a Phase 2a clinical trial for reducing the number of reflux episodes in patients with gastroesophageal reflux disease, or GERD. Our current portfolio of proprietary product candidates includes the following:

	•		XP13512 for RLS. XP13512 is a Transported Prodrug of gabapentin. XP13512 is currently being evaluated in a Phase 3 clinical program for the treatment of RLS. RLS is characterized by an irresistible urge to move one’s legs, usually accompanied by unpleasant sensations or pain in the legs. On April 25, 2007, we announced top-line results from a Phase 3 clinical trial of XP13512 for the treatment of symptoms of primary RLS. XP13512 demonstrated statistically significant improvements compared to placebo on both of the co-primary endpoints of the trial and was well tolerated.
	•		XP13512 for Neuropathic Pain, Including PHN. We have also shown in a Phase 2a clinical trial that XP13512 is effective for the management of PHN, a chronic type of neuropathic pain that can follow the resolution of shingles.
	•		XP19986 for GERD and Spasticity. XP19986 is a Transported Prodrug of R-baclofen that is in development for the treatment of GERD, which is a digestive system disorder caused primarily by inappropriate relaxations of the lower esophageal sphincter, which is a combination of muscles that controls the junction between the esophagus and the stomach. GERD is characterized by the frequent, undesirable passage of stomach contents into the esophagus that results in discomfort and potential damage to the lining of the esophagus. We have successfully completed a Phase 2a clinical trial indicating that single doses of XP19986 were well tolerated and produced statistically significant reductions in the number of reflux episodes in patients with GERD. XP19986 is also a potential treatment for the symptoms of spasticity.
	•		XP21279 for Parkinson’s Disease. XP21279 is a Transported Prodrug of levodopa, or L-Dopa, that is in preclinical development for the treatment of Parkinson’s disease. We plan to file an investigational new drug application, or IND, for XP21279 in the fourth quarter of 2007.
	•		XP20925 for Migraine and Chemotherapy-Induced Nausea and Vomiting. XP20925 is a Transported Prodrug of propofol that is in preclinical development for the treatment of migraine and chemotherapy-induced nausea and vomiting. We plan to commence preclinical development activities to support the filing in 2008 of an IND for XP20925.

     We were incorporated in May 1999 and commenced active operations in August 1999. To date, we have not generated any product revenues. We have funded our operations primarily through the sale of equity securities, non-equity payments from collaborative partners, capital lease financings, interest earned on investments and government grants. We have incurred net losses since inception and expect to incur losses for the next several years as we expand our research and development activities and move our product candidates into later stages of development. We expect our research and development expenses to continue to increase as we expand our development programs, and, subject to regulatory approval of any of our product candidates, we expect to incur significant expenses associated with the establishment of a North American specialty sales force. Because of the numerous risks and uncertainties associated with drug development, we are unable to predict the timing or amount of increased expenses if we establish a North American specialty sales force. As of March 31, 2007, we had an accumulated deficit of approximately $207.6 million.

     From our inception in 1999 through 2001, our principal activities were focused on identifying and characterizing natural nutrient transporter mechanisms and developing the technology necessary to utilize them for the active transport of drugs. Beginning in 2002, our activities expanded to include the preclinical and clinical development of internally discovered product candidates based on this proprietary technology. In addition to our ongoing research program, the process of carrying out the development of our product candidates to later stages of development will require significant additional research and development expenditures, including preclinical testing, clinical trials, manufacturing development efforts and regulatory activities. We outsource a substantial portion of our preclinical studies, clinical trials and manufacturing activities to third parties to maximize efficiency and minimize our internal overhead.

     In December 2005, we entered into an agreement in which we licensed to Astellas Pharma Inc. exclusive rights to develop and commercialize XP13512 in Japan, Korea, the Philippines, Indonesia, Thailand and Taiwan (collectively referred to as the Astellas territory). We received an initial license payment of $25.0 million. The terms of the agreement also specify clinical and regulatory milestone payments totaling up to a maximum of $60.0 million, including milestone payments of $10.0 million upon initiation of our first Phase 3 clinical trial of XP13512 in RLS patients in the United States, which we received in April 2006, and $5.0 million at the completion of our first Phase 3 clinical trial of XP13512 in RLS patients in the United States, which we expect to receive in May 2007. We will receive royalties on any sales of XP13512 in the Astellas territory at a royalty rate in the mid-teens on a percentage basis. As of March 31, 2007, we had recognized an aggregate of $12.0 million of revenue pursuant to this agreement.

     In February 2007, we announced an exclusive collaboration with Glaxo Group Limited, or GSK, to develop and commercialize XP13512 worldwide, excluding the Astellas territory. GSK made an up-front, non-refundable license payment to us of $75.0 million that we received in March 2007, and GSK has agreed to make additional payments of up to $275.0 million upon the achievement of pre-commercialization milestones and up to $290.0 million upon the achievement of specified sales levels. Under the terms of the agreement, GSK is responsible for all future development costs, with the exception of specified development costs that we assumed in connection with the development of XP13512 for RLS in the United States. We are entitled to receive royalties based upon a percentage of sales of XP13512 in the GSK territory for a specified period of time, unless we elect the option to co-promote XP13512 in the United States. In the event that we elect the co-promotion option for XP13512, we would share marketing and commercialization costs and would be entitled to a share of operating profits from sales of XP13512 in the United States for so long as XP13512 is sold, as well as payments on details we perform in the United States on Requip CR and Requip XL 24-Hour, GSK’s development-stage product candidates for RLS and Parkinson’s disease, respectively. Subject to FDA approval of the new drug application, or NDA, for XP13512, we would co-promote XP13512 in the United States to those same prescribers. As of March 31, 2007, we had recognized an aggregate of $15.3 million of revenue pursuant to this agreement. In April 2007, we satisfied the criteria to receive a $10.0 million milestone payment under this agreement, and we expect to receive this milestone payment in May 2007.

Critical Accounting Policies and Significant Judgments and Estimates

     Our management’s discussion and analysis of our financial condition and results of operations is based on our financial statements, which have been prepared in accordance with accounting principles generally accepted in the United States. The preparation of these financial statements requires us to make estimates and assumptions that affect the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements, as well as the reported revenues and expenses during the reporting periods. On an ongoing basis, we evaluate our estimates and judgments related to revenue recognition and clinical development costs. We base our estimates on historical experience and on various other factors that we believe are reasonable under the circumstances, the results of which form the basis for making judgments about the carrying value of assets and liabilities that are not readily apparent from other sources. Actual results may differ from these estimates under different assumptions or conditions. Our critical accounting policies and significant judgments and estimates are detailed in our annual report on Form 10-K with the exception of the following revenue recognition policy which has been updated subsequent to the initiation of our collaboration with GSK and additions to our stock-based compensation policy which has been updated to reflect our recent grants of restricted stock units.

Revenue Recognition

     We have entered into collaboration agreements with Astellas, ALZA Corporation, GSK and Pfizer Inc, each of which contains multiple elements. We account for these agreements in accordance with the provisions of Securities and Exchange Commission, or SEC, Staff Accounting Bulletin, or SAB, No. 101, Revenue Recognition in Financial Statements, superceded by SAB No. 104, Revenue Recognition, and Emerging Issues Task Force, or EITF, No. 00-21, Revenue Arrangements with Multiple Deliverables. We considered a variety of factors in determining the appropriate method of revenue recognition under these arrangements, such as whether the various elements can be considered separate units of accounting, whether there is objective and reliable evidence of fair value for these elements and whether there is a separate earnings process associated with a particular element of an agreement. Specifically, we account for each of these typical elements as follows:

	•		Up-front, licensing-type fees. To date, these types of fees have been classified within the collaboration agreements as license fees, access fees, rights fees and initial licensing fees, and each of them was non-refundable and payable in connection with the execution of the contract. Up-front, licensing-type payments are assessed to determine whether or not the licensee is able to obtain any stand-alone value from the license. Where this is not the case, we do not consider the license deliverable to be a separate unit of accounting and we defer the revenue with revenue recognition for the license fee being assessed in conjunction with the other deliverables that constitute the combined unit of accounting.
	•		Milestones. We assess milestones on an individual basis and recognize revenue from these milestones when earned, as evidenced by acknowledgment from our collaborator, provided that (i) the milestone event is substantive and its achievability was not reasonably assured at the inception of the agreement, (ii) the milestone represents the culmination of, or progress towards the culmination of, an earnings process and (iii) the milestone payment is non-refundable. Where separate milestones do not meet these criteria, we typically default to a performance-based model, with revenue recognition following delivery of effort as compared to an estimate of total expected effort. Milestones that are received after all substantive deliverables have occurred are considered to be bonus payments and are recognized upon receipt of the cash, assuming all of the other revenue recognition criteria are met.

	•		Collaborative research payments. Generally, the payments received are based on a contractual cost per full-time equivalent employee working on the project, and we recognize revenue related to these payments as the services are performed over the related funding periods for each agreement.
	•		Grant revenues. Grant revenues are recognized as research is performed. Grant revenues are non-refundable.
	•		Combined units of accounting. Where there are multiple deliverables combined as a single unit of accounting, revenues are deferred and recognized over the longest period over which we remain obligated to perform services or deliver product. The specific methodology for the recognition of the revenue (e.g., straight-line or according to specific performance criteria) is determined on a case-by-case basis according to the facts and circumstances applicable to a given contract.

     Our collaboration agreements also include potential payments for commercial product supply and product royalties. To date, we have not received revenue from either of these sources.

Stock-Based Compensation

     Restricted stock units are measured at the fair value of the common stock on the date of grant and expensed over the period of vesting using the straight-line attribution approach.

     Our accounting policies related to stock options and stock-based compensation arrangements to employees and non-employees has not changed from those detailed in our most recent annual report on Form 10-K.

Results of Operations

Three Months Ended March 31, 2007 and 2006

     Revenues

     Our revenues consisted of amounts earned from our collaborations with Astellas and GSK.

		Three Months
		Ended
		March 31,								Change
		2007				2006				$				%
		(in thousands, except percentages)
Revenues		$	16,539			$	1,288			$	15,251				1,184	%

     The increase in revenues of $15.3 million for the three months ended March 31, 2007 compared to the same period in 2006 was the result of revenues recognized under our GSK agreement that was executed in February 2007.

     We expect revenues to fluctuate during the remainder of 2007 and beyond primarily depending upon our progress against the deliverables specified in the terms of our collaboration with GSK, the timing of milestone-related activities under our Astellas collaboration and the extent to which we enter into new collaborative agreements.

     Research and Development Expenses

     Research and development expenses consist of costs associated with our research activities and drug discovery efforts, as well as costs associated with conducting preclinical studies and clinical trials, manufacturing development efforts and activities related to regulatory filings. Of the total research and development expenses for the three months ended March 31, 2007 and 2006, the allocation of costs associated with research and preclinical and clinical development activities was as follows:

		Three Months
		Ended
		March 31,								Change
		2007				2006				$				%
		(in thousands, except percentages)
Research and preclinical		$	4,353			$	4,181			$	172				4	%
Clinical development			12,736				9,565				3,171				33	%
Total research and development		$	17,089			$	13,746			$	3,343				24	%

     The increase in research and development expenses in the three months ended March 31, 2007 compared to the same period in 2006 was primarily due to the following factors:

	•		XP13512 clinical trial costs increased by $3.8 million, partially offset by a $2.0 million decrease in manufacturing costs;
	•		XP19986 clinical trial costs decreased by $0.3 million and manufacturing costs decreased by $0.2 million, due to the completion of Phase 2 clinical trials; and
	•		personnel costs increased by $1.5 million and consulting costs increased by $0.4 million.

     We expect that research and development expenses will increase in the future due to increased clinical development costs primarily relating to our XP13512 and XP19986 programs. The timing and amount of these expenses will primarily depend upon the costs associated with our Phase 3 clinical program in RLS for XP13512 and the outcome of future clinical trials for XP19986, as well as the related expansion of our research and development organization, regulatory requirements, advancement of our preclinical programs and product candidate manufacturing costs.

     General and Administrative Expenses

     General and administrative expenses consist principally of salaries and other related costs for personnel in executive, finance, accounting, business development, information technology, legal and human resources functions. Other general and administrative expenses include facility costs not otherwise included in research and development expenses, patent-related costs and professional fees for legal, consulting and accounting services.

		Three Months
		Ended
		March 31,								Change
		20067				2006				$				%
		(in thousands, except percentages)
General and administrative		$	4,403			$	3,406			$	997				29	%

     The increase in general and administrative expenses in the three months ended March 31, 2007 compared to the same period in 2006 was primarily due to increased personnel costs of $0.4 million, marketing fees of $0.2 million and office-related expenses of $0.2 million.

     We expect that general and administrative expenses will increase in the future due to increased personnel, expanded infrastructure and increased consulting and legal services.

     Interest Income and Interest Expense

     Interest income consists of interest earned on our cash and cash equivalents and short-term investments.

		Three Months
		Ended
		March 31,								Change
		2007				2006				$				%
		(in thousands, except percentages)
Interest income		$	1,657			$	937			$	720				77	%
Interest and other expense		$	53			$	51			$	2				4	%

     The increase in interest income in the three months ended March 31, 2007 compared to the same period in 2006 was due primarily to higher average balances due to funds received from our follow-on offering in June 2006 and the initial license payment from GSK in March 2007 and higher average interest rates in 2007.

Financial Condition, Liquidity and Capital Resources

		As of				As of
		March				December
		31,				31,
		2007				2006
		(in thousands)
Cash and cash equivalents and short-term investments		$	171,436			$	118,854
Working capital			99,950				101,527
Restricted investments			1,720				1,699
Current portions of equipment financing and capital lease obligations			403				500
Noncurrent portions of equipment financing and capital lease obligations			121				181

		Three Months
		Ended
		March 31,
		2007				2006
		(in thousands)
Cash provided by (used in):
Operating activities		$	51,904			$	(13,412	)
Investing activities			(8,491	)			10,185
Financing activities			182				(78	)
Capital expenditures (included in investing activities above)			(546	)			(218	)

     Due to our significant research and development expenditures and the lack of regulatory agency approvals to sell any products, we have not been profitable and have generated operating losses since we incorporated in 1999. As such, we have funded our operations primarily through sales of our preferred stock and through our public offerings. As of March 31, 2007, we had derived aggregate net proceeds of $151.5 million from sales of our preferred stock, $46.3 million from our initial public offering in 2005 and $73.8 million from our follow-on public offering in 2006. We have received additional funding from non-equity payments from collaborative partners, capital lease financings, interest earned on investments and government grants, each as described more fully below. At March 31, 2007, we had available cash and cash equivalents and short-term investments of $171.4 million. Our cash and investment balances are held in a variety of interest-bearing instruments, including obligations of corporate debt securities and money market accounts. Cash in excess of immediate requirements is invested with regard to liquidity and capital preservation. Wherever possible, we seek to minimize the potential effects of concentration and degrees of risk.

     Net cash provided by (used in) operating activities was $51.9 million and $(13.4) million in the three months ended March 31, 2007 and 2006, respectively. The net cash provided by operating activities in the three months ended March 31, 2007 primarily reflected our net loss, offset by an increase in deferred revenue in connection with our February 2007 agreement with GSK. The net cash used in operating activities in the three months ended March 31, 2006 primarily reflected our net loss, offset in part by depreciation, non-cash stock-based compensation and non-cash changes in operating assets and liabilities.

     Net cash provided by (used in) investing activities was $(8.5) million and $10.2 million in the three months ended March 31, 2007 and 2006, respectively. Cash used in investing activities for the three months ended March 31, 2007 was primarily related to the purchases of investments, offset by proceeds from maturities of investments. Cash provided by investing activities for the three months ended March 31, 2006 was primarily related to the proceeds from maturities of investments, offset by purchases of investments and, to a lesser extent, purchases of property and equipment.

     Net cash provided by (used in) financing activities was $0.2 million and $(0.1) million in the three months ended March 31, 2007 and 2006, respectively. For the three months ended March 31, 2007, cash was primarily provided by proceeds from stock option exercises, offset by principal payments on capital leases. For the three months ended March 31, 2006, cash was primarily used in principal payments on capital leases, offset by proceeds from stock option exercises.

     We believe that our existing capital resources and expected milestone payments, together with interest thereon, will be sufficient to meet our projected operating requirements into the third quarter of 2009. We have based this estimate on assumptions that may prove to be wrong, and we could utilize our available capital resources sooner than we currently expect. Our forecast of the period of time through which our financial resources will be adequate to support our operations is a forward-looking statement and involves risks and uncertainties, and actual results could vary as a result of a number of factors, including the factors discussed in “Risk Factors.” Because of the numerous risks and uncertainties associated with the development and commercialization of our product candidates, and the extent to which we enter into additional collaborations with third parties to participate in their development and commercialization, we are unable to estimate the amounts of increased capital outlays and operating expenditures associated with our current and anticipated clinical trials. Our future funding requirements will depend on many factors, including:

	•		the scope, rate of progress, results and cost of our preclinical testing, clinical trials and other research and development activities;
	•		the cost of manufacturing clinical and establishing commercial supplies of our product candidates and any products that we may develop;
	•		the timing of any milestone payments under our collaborative arrangements;
	•		the cost, timing and outcomes of regulatory approvals;
	•		the number and characteristics of product candidates that we pursue;
	•		the cost and timing of establishing sales, marketing and distribution capabilities;
	•		the terms and timing of any other collaborative, licensing and other arrangements that we may establish;
	•		the timing, receipt and amount of sales or royalties, if any, from our potential products;
	•		the cost of preparing, filing, prosecuting, defending and enforcing any patent claims and other intellectual property rights; and
	•		the extent to which we acquire or invest in businesses, products or technologies, although we currently have no commitments or agreements relating to any of these types of transactions.

     If we need to raise additional money to fund our operations, funding may not be available to us on acceptable terms, or at all. If we are unable to raise additional funds when needed, we may not be able to continue development of our product candidates or we could be required to delay, scale back or eliminate some or all of our research and development programs. We may seek to raise any necessary additional funds through equity or debt financings, collaborative arrangements with corporate partners or other sources. To the extent that we raise additional capital through licensing arrangements or arrangements with collaborative partners, we may be required to relinquish, on terms that are not favorable to us, rights to some of our technologies or product candidates that we would otherwise seek to develop or commercialize ourselves. To the extent that we raise additional capital through equity financings, dilution to our stockholders would result.

Contractual Obligations

     Our future contractual obligations at March 31, 2007 were as follows (in thousands):

		Payments Due by Period
						Less
						Than				1-3				3-5
Contractual Obligations		Total				1 Year				Years				Years
Equipment financing obligations		$	554			$	429			$	125			$	—
Operating lease obligations			19,116				3,863				8,106				7,147
Total fixed contractual obligations		$	19,670			$	4,292			$	8,231			$	7,147

Item 3. Quantitative and Qualitative Disclosures About Market Risk

     The primary objective of our investment activities is to preserve our capital to fund operations. We also seek to maximize income from our investments without assuming significant risk. To achieve our objectives, we maintain a portfolio of cash equivalents and investments in a variety of securities of high credit quality. As of March 31, 2007, we had cash and cash equivalents and short-term investments of $171.4 million consisting of cash and highly liquid investments deposited in a highly rated financial institution in the United States. A portion of our investments may be subject to interest rate risk and could fall in value if market interest rates increase. However, because our investments are short-term in duration, we believe that our exposure to interest rate risk is not significant and a 1% movement in market interest rates would not have a significant impact on the total value of our portfolio. We actively monitor changes in interest rates.

     We contract for the conduct of certain manufacturing activities with a contract manufacturer in Europe. We made payments in the aggregate amount of approximately $4.5 million and zero for the three months ended March 31, 2007 and 2006, respectively, to this European contract manufacturer. We may be subject to exposure to fluctuations in foreign exchange rates in connection with these agreements. To date, the effect of the exposure to these fluctuations in foreign exchange rates has not been material, and we do not expect it to be material in the foreseeable future. We do not hedge our foreign currency exposures. We have not used derivative financial instruments for speculation or trading purposes.

Item 4. Controls and Procedures

     Evaluation of Disclosure Controls and Procedures.

     Based on the evaluation of our disclosure controls and procedures (as defined in Rules 13a-15(e) and 15d-15(e) under the Securities Exchange Act of 1934, as amended, or Securities Exchange Act) required by Rules 13a-15(b) or 15d-15(b) under the Securities Exchange Act, our chief executive officer and chief financial officer have concluded that, as of the end of the period covered by this report, our disclosure controls and procedures were effective.

     Changes in Internal Controls over Financial Reporting.

     There were no changes in our internal controls over financial reporting during the period covered by this report that have materially affected, or are reasonably likely to materially affect, our internal control over financial reporting.

PART II. OTHER INFORMATION

Item 1. Legal Proceedings

None.

Item 1A. Risk Factors

     The following risks and uncertainties may have a material adverse effect on our business, financial condition or results of operations. Investors should carefully consider the risks described below before making an investment decision. The risks described below are not the only ones we face. Additional risks not presently known to us or that we currently believe are immaterial may also significantly impair our business operations. Our business could be harmed by any of these risks. The trading price of our common stock could decline due to any of these risks, and investors may lose all or part of their investment.

     We have marked with an asterisk (*) those risk factors below that reflect substantive changes from the risk factors included in our Annual Report on Form 10-K filed with the Securities and Exchange Commission on March 7, 2007.

Risks Related to Our Business and Industry

     We have incurred operating losses since inception and expect to continue to incur losses for the foreseeable future. We may never achieve or sustain profitability.*

     We have a limited operating history and have incurred significant losses since our inception, including losses of approximately $3.3 million for the three months ended March 31, 2007 and $207.6 million since our inception in May 1999. We expect our research and development expenses to continue to increase as we expand our development programs and, subject to regulatory approval for any of our product candidates, we expect to incur significant expenses associated with the establishment of a North American specialty sales force. As a result, we expect to continue to incur annual losses for the foreseeable future. These losses have had, and will continue to have, an adverse effect on our stockholders’ equity.

     Because of the numerous risks and uncertainties associated with drug development, we are unable to predict the timing or amount of increased expenses or when or if we will be able to achieve or sustain profitability. Currently, we have no products approved for commercial sale and, to date, we have not generated any product revenues. We have financed our operations primarily through the sale of equity securities, non-equity payments from collaborative partners, capital lease and equipment financings and government grants. We have devoted substantially all of our efforts to research and development, including clinical trials. If we or our collaborative partners are unable to develop and commercialize any of our product candidates, if development is delayed or if sales revenue from any product candidate that receives marketing approval is insufficient, we may never become profitable. Even if we do become profitable, we may not be able to sustain or increase our profitability on a quarterly or annual basis.

     Our success depends substantially on our most advanced product candidates, which are still under development. If we or our collaborative partners are unable to bring any or all of these product candidates to market, or experience significant delays in doing so, our ability to generate product revenue and our likelihood of success will be harmed.

     Our ability to generate product revenue in the future will depend heavily on the successful development and commercialization of our product candidates. Our most advanced product candidate is currently being evaluated in a Phase 3 clinical program. Our other product candidates are either in Phase 2 clinical development or in various stages of preclinical development. Any of our product candidates could be unsuccessful if it:

	•		does not demonstrate acceptable safety and efficacy in preclinical studies or clinical trials or otherwise does not meet applicable regulatory standards for approval;
	•		does not offer therapeutic or other improvements over existing or future drugs used to treat the same conditions;
	•		is not capable of being produced in commercial quantities at acceptable costs; or
	•		is not accepted in the medical community or by third-party payors.

     We do not expect any of our current product candidates to be commercially available before 2009, if at all. If we or our collaborative partners are unable to make our product candidates commercially available, we will not generate substantial product revenue and we will not be successful. The results of our clinical trials to date do not provide assurance that acceptable efficacy or safety will be shown upon completion of future Phase 3 clinical trials.

     If we or our partners are not able to obtain required regulatory approvals, we or our partners will not be able to commercialize our product candidates, our ability to generate revenue will be materially impaired and our business will not be successful.*

     Our product candidates and the activities associated with their development and commercialization are subject to comprehensive regulation by the U.S. Food and Drug Administration, or FDA, and other regulatory agencies in the United States and by comparable authorities in other countries. In February 2007, we announced an exclusive collaboration with Glaxo Group Limited, or GSK, to develop and commercialize XP13512 in all countries of the world other than the six countries that comprise the territory under our collaboration with Astellas Pharma Inc. Under the terms of our agreement, GSK would file the new drug application, or NDA, for restless legs syndrome, or RLS, for FDA approval, and GSK would lead the development and registration of XP13512 for all indications, including neuropathic pain, other than RLS in the United States and all indications in the remainder of GSK’s licensed territory. The inability to obtain FDA approval or approval from comparable authorities in other countries would prevent us and our collaborative partners from commercializing our product candidates in the United States or other countries. We or our collaborative partners may never receive regulatory approval for the commercial sale of any of our product candidates. Moreover, if the FDA requires that any of our product candidates be scheduled by the U.S. Drug Enforcement Agency, or DEA, we or our collaborative partners will be unable to begin commercial sale of that product until the DEA completes scheduling proceedings. If any of our product candidates is classified as a controlled substance by the DEA, we or our collaborative partners would have to register annually with the DEA and those product candidates would be subject to additional regulation. Neither we nor our collaborative partners have received regulatory approval to market any of our product candidates in any jurisdiction. We have only limited experience in preparing and filing the applications necessary to gain regulatory approvals. The process of applying for regulatory approval is expensive, often takes many years and can vary substantially based upon the type, complexity and novelty of the product candidates involved.

     Changes in the regulatory approval policy during the development period, changes in, or the enactment of additional, regulations or statutes or changes in regulatory review for each submitted product application may cause delays in the approval or rejection of an application. Even if the FDA or other regulatory agency approves a product candidate, the approval may impose significant restrictions on the indicated uses, conditions for use, labeling, advertising, promotion, marketing and/or production of such product and may impose ongoing requirements for post-approval studies, including additional research and development and clinical trials. The FDA and other agencies also may impose various civil or criminal sanctions for failure to comply with regulatory requirements, including withdrawal of product approval.

     The FDA has substantial discretion in the approval process and may refuse to accept any application or decide that our or our collaborative partners’ data is insufficient for approval and require additional preclinical, clinical or other studies. For example, varying interpretations of the data obtained from preclinical and clinical testing could delay, limit or prevent regulatory approval of any of our product candidates.

     We and our collaborative partners will need to obtain regulatory approval from authorities in foreign countries to market our product candidates in those countries. Neither we nor our collaborative partners have initiated the regulatory approval process in any foreign jurisdictions. Approval by one regulatory authority does not ensure approval by regulatory authorities in other jurisdictions. If we or our collaborative partners fail to obtain approvals from foreign jurisdictions, the geographic market for our product candidates would be limited.

     We depend on collaborations to complete the development and commercialization of some of our product candidates. These collaborations may place the development of our product candidates outside our control, may require us to relinquish important rights or may otherwise be on terms unfavorable to us.*

     In December 2005, we entered into a collaboration with Astellas for the development and commercialization of XP13512 in Japan and five other Asian countries. In February 2007, we entered into an exclusive collaboration with GSK to develop and commercialize XP13512 worldwide, excluding the Astellas territory. We may enter into additional collaborations with third parties to develop and commercialize some of our other product candidates. Our dependence on Astellas and GSK for the development and commercialization of XP13512 subjects us to, and dependence on future collaborators for development and commercialization of additional product candidates will subject us to, a number of risks, including:

	•		we may not be able to control the amount and timing of resources that our collaborators may devote to the development or commercialization of product candidates or to their marketing and distribution;
	•		collaborators may delay clinical trials, provide insufficient funding for a clinical trial program, stop a clinical trial or abandon a product candidate, repeat or conduct new clinical trials or require a new formulation of a product candidate for clinical testing;

	•		disputes may arise between us and our collaborators that result in the delay or termination of the research, development or commercialization of our product candidates or that result in costly litigation or arbitration that diverts management’s attention and resources;
	•		collaborators may experience financial difficulties;
	•		collaborators may not properly maintain or defend our intellectual property rights or may use our proprietary information in such a way as to invite litigation that could jeopardize or invalidate our proprietary information or expose us to potential litigation;
	•		business combinations or significant changes in a collaborator’s business strategy may also adversely affect a collaborator’s willingness or ability to complete its obligations under any arrangement;
	•		a collaborator could independently move forward with a competing product candidate developed either independently or in collaboration with others, including our competitors; and
	•		the collaborations may be terminated or allowed to expire, which would delay the development and may increase the cost of developing our product candidates.

     For example, pursuant to the terms of our agreement, GSK is responsible for all future development costs of XP13512, with the exception of specified development costs that we assumed in connection with the development of XP13512 for RLS in the United States. In addition, subject to additional positive Phase 3 clinical data, GSK is obligated to file the NDA for RLS for FDA approval, and GSK would lead the development and registration of XP13512 for all indications, including neuropathic pain, other than RLS in the United States and all indications in the remainder of GSK’s licensed territory. We cannot control the amount and timing of resources that GSK may devote to the development or commercialization of XP13512 or to its marketing and distribution. In addition, GSK could independently direct its development and marketing resources to the development or commercialization of competitive products, which could delay or impair the commercialization of XP13512 and harm our business.

     If we do not establish collaborations for XP19986 or our product candidates other than XP13512, we will have to alter our development and commercialization plans.

     Our strategy includes selectively collaborating with leading pharmaceutical and biotechnology companies to assist us in furthering development and potential commercialization of some of our product candidates, including XP19986. We intend to do so especially for indications that involve a large, primary care market that must be served by large sales and marketing organizations. We face significant competition in seeking appropriate collaborators, and these collaborations are complex and time consuming to negotiate and document. We may not be able to negotiate additional collaborations on acceptable terms, or at all. We are unable to predict when, if ever, we will enter into any additional collaborations because of the numerous risks and uncertainties associated with establishing additional collaborations. If we are unable to negotiate additional collaborations, we may have to curtail the development of a particular product candidate, reduce or delay its development program or one or more of our other development programs, delay its potential commercialization or reduce the scope of our sales or marketing activities or increase our expenditures and undertake development or commercialization activities at our own expense. If we elect to increase our expenditures to fund development or commercialization activities on our own, we may need to obtain additional capital, which may not be available to us on acceptable terms, or at all. If we do not have sufficient funds, we will not be able to bring our product candidates to market and generate product revenues.

     We will need additional funding and may be unable to raise capital when needed, which would force us to delay, reduce or eliminate our product development programs or commercialization efforts. *

     We will need to raise additional capital to fund our operations and complete the development of our product candidates. If any product candidates receive regulatory approval for commercial sale, we may need to raise additional capital to fund our commercialization efforts. Our future funding requirements will depend on many factors, including:

	•		the scope, rate of progress, results and cost of our preclinical testing, clinical trials and other research and development activities;
	•		the cost of manufacturing clinical and establishing commercial supplies of our product candidates and any products that we may develop;
	•		the timing of any milestone payments under our collaborative arrangements;
	•		the number and characteristics of product candidates that we pursue;
	•		the cost, timing and outcomes of regulatory approvals;
	•		the cost and timing of establishing sales, marketing and distribution capabilities;
	•		the terms and timing of any collaborative, licensing and other arrangements that we may establish;
	•		the timing, receipt and amount of sales or royalties, if any, from our potential products;
	•		the cost of preparing, filing, prosecuting, defending and enforcing any patent claims and other intellectual property rights; and
	•		the extent to which we acquire or invest in businesses, products or technologies, although we currently have no commitments or agreements relating to any of these types of transactions.

     Until we can generate a sufficient amount of product revenues, if ever, we expect to finance future cash needs through public or private equity offerings, debt financings or corporate collaboration and licensing arrangements, as well as through interest income earned on cash balances.

     If we raise additional funds by issuing equity securities, our stockholders may experience dilution. Any debt financing or additional equity that we raise may contain terms that are not favorable to our stockholders or us. If we raise additional funds through collaboration and licensing arrangements with third parties, we may be required to relinquish some rights to our technologies or our product candidates or grant licenses on terms that are not favorable to us.

     We believe that our existing capital resources and expected milestone payments, together with interest thereon, will be sufficient to meet our projected operating requirements into the third quarter of 2009. However, our operating plan may change, and we may need additional funds to meet operational needs and capital requirements for product development and commercialization sooner than planned. We currently have no credit facility or committed sources of capital other than potential milestones receivable under our collaborations.

     Additional funds may not be available when we need them on terms that are acceptable to us, or at all. If adequate funds are not available on a timely basis, we may:

	•		terminate or delay clinical trials for one or more of our product candidates;
	•		delay our establishment of sales and marketing capabilities or other activities that may be necessary to commercialize our product candidates; or
	•		curtail significant drug development programs that are designed to identify new product candidates.

     If our preclinical studies do not produce successful results or our clinical trials do not demonstrate safety and efficacy in humans, we will not be able to commercialize our product candidates.

     To obtain the requisite regulatory approvals to market and sell any of our product candidates, we must demonstrate, through extensive preclinical studies and clinical trials, that the product candidate is safe and effective in humans. Preclinical and clinical testing is expensive, can take many years and has an uncertain outcome. A failure of one or more of our clinical trials could occur at any stage of testing. In addition,

success in preclinical testing and early clinical trials does not ensure that later clinical trials will be successful, and interim results of a clinical trial do not necessarily predict final results. We may experience numerous unforeseen events during, or as a result of, preclinical testing and the clinical trial process, which could delay or prevent our or our collaborative partners’ ability to commercialize our product candidates, including:

	•		regulators or institutional review boards may not authorize us to commence a clinical trial at a prospective trial site;
	•		our preclinical testing or clinical trials may produce negative or inconclusive results, which may require us to conduct additional preclinical or clinical testing or to abandon projects that we expect to be promising;
	•		we may suspend or terminate our clinical trials if the participating patients are being exposed to unacceptable health risks;
	•		regulators or institutional review boards may suspend or terminate clinical research for various reasons, including noncompliance with regulatory requirements; and
	•		the effects of our product candidates may not be the desired effects or may include undesirable side effects.

     As an example of an unforeseen event, after having been discharged from a Phase 1 clinical trial in which a single dose of XP13512 was administered almost two days earlier, a volunteer died of a self-inflicted gunshot wound following a domestic dispute. We do not believe that this incident was related to XP13512. However, any unforeseen event could cause us to experience significant delays in, or the termination of, clinical trials. Any such events would increase our costs and could delay or prevent our ability to commercialize our product candidates, which would adversely impact our financial results.

     Any failure or delay in commencing or completing clinical trials for our product candidates could severely harm our business.

     To date, we have not completed all of the clinical trials required for regulatory approval of any product candidate. The commencement and completion of clinical trials for our product candidates may be delayed or terminated as a result of many factors, including:

	•		our inability or the inability of our collaborators or licensees to manufacture or obtain from third parties materials sufficient for use in preclinical studies and clinical trials;
	•		delays in patient enrollment, which we have experienced in the past, and variability in the number and types of patients available for clinical trials;
	•		difficulty in maintaining contact with patients after treatment, resulting in incomplete data;
	•		poor effectiveness of product candidates during clinical trials;
	•		unforeseen safety issues or side effects; and
	•		governmental or regulatory delays and changes in regulatory requirements, policy and guidelines.

     Any delay in commencing or completing clinical trials for our product candidates would delay commercialization of our product candidates and severely harm our business and financial condition. It is also possible that none of our product candidates will complete clinical trials in any of the markets in which we or our collaborators intend to sell those product candidates. Accordingly, we or our collaborators would not receive the regulatory approvals needed to market our product candidates, which would severely harm our business and financial condition.

     We rely on third parties to conduct our clinical trials. If these third parties do not perform as contractually required or expected, we may not be able to obtain regulatory approval for, or commercialize, our product candidates. *

     We do not have the ability to independently conduct clinical trials for our product candidates, and we must rely on third parties, such as contract research organizations, medical institutions, clinical investigators, collaborative partners and contract laboratories, to conduct

our clinical trials. We have, in the ordinary course of business, entered into agreements with these third parties. Nonetheless, with the exception of XP13512 outside the United States for RLS and all other indications around the world, we are responsible for confirming that each of our clinical trials is conducted in accordance with its general investigational plan and protocol. Moreover, the FDA requires us to comply with regulations and standards, commonly referred to as good clinical practices, for conducting and recording and reporting the results of clinical trials to assure that data and reported results are credible and accurate and that the trial participants are adequately protected. Our reliance on third parties that we do not control does not relieve us of these responsibilities and requirements. For example, we need to prepare, and ensure our compliance with, various procedures required under good clinical practices, even though third-party contract research organizations have prepared and are complying with their own, comparable procedures. If these third parties do not successfully carry out their contractual duties or regulatory obligations or meet expected deadlines, if the third parties need to be replaced or if the quality or accuracy of the data they obtain is compromised due to the failure to adhere to our clinical protocols or regulatory requirements or for other reasons, our preclinical development activities or clinical trials may be extended, delayed, suspended or terminated, and we may not be able to obtain regulatory approval for, or successfully commercialize, our product candidates. For example, one of our third-party contract research organizations was acquired by another company, and if such acquisition delays or prevents them from successfully carrying out their contractual duties to us, there could be a delay in commencing or completing clinical trials for our product candidates that could delay commercialization of our product candidates.

     If some or all of our patents expire, are invalidated or are unenforceable, or if some or all of our patent applications do not yield issued patents or yield patents with narrow claims, competitors may develop competing products using our intellectual property and our business will suffer.*

     Our success will depend in part on our ability to obtain and maintain patent and trade secret protection for our technologies and product candidates both in the United States and other countries. We cannot guarantee that any patents will issue from any of our pending or future patent applications. Alternatively, a third party may successfully circumvent our patents. Our rights under any issued patents may not provide us with sufficient protection against competitive products or otherwise cover commercially valuable products or processes.

     The degree of future protection for our proprietary technologies and product candidates is uncertain because legal means afford only limited protection and may not adequately protect our rights or permit us to gain or keep our competitive advantage. For example:

	•		we might not have been the first to make the inventions covered by each of our pending patent applications and issued patents;
	•		we might not have been the first to file patent applications for these inventions;
	•		others may independently develop similar or alternative technologies or duplicate any of our technologies;
	•		it is possible that none of our pending patent applications will result in issued patents;
	•		any patents issued to us or our collaborators may not provide a basis for commercially viable products or may be challenged by third parties; or
	•		the patents of others may have an adverse effect on our ability to do business.

     Even if valid and enforceable patents cover our product candidates and technologies, the patents will provide protection only for a limited amount of time.

     Our and our collaborators’ ability to obtain patents is highly uncertain because, to date, some legal principles remain unresolved, there has not been a consistent policy regarding the breadth or interpretation of claims allowed in patents in the United States and the specific content of patents and patent applications that are necessary to support and interpret patent claims is highly uncertain due to the complex nature of the relevant legal, scientific and factual issues. Furthermore, the policies governing biotechnology patents outside the United States are even more uncertain. Changes in either patent laws or interpretations of patent laws in the United States and other countries may diminish the value of our intellectual property or narrow the scope of our patent protection.

     Even if patents are issued regarding our product candidates or methods of using them, those patents can be challenged by our competitors who can argue such patents are invalid and/or unenforceable. Patents also may not protect our product candidates if competitors devise ways of making these or similar product candidates without legally infringing our patents. The Federal Food, Drug and Cosmetic Act and FDA regulations and policies provide incentives to manufacturers to challenge patent validity and these same types of incentives encourage manufacturers to submit new drug applications that rely on literature and clinical data not prepared for or by the drug sponsor.

     As of April 15, 2007, we held 20 U.S. patents and had 89 patent applications pending before the U.S. Patent and Trademark Office, or PTO. For some of our inventions, corresponding non-U.S. patent protection is pending. Of the 20 U.S. patents that we hold, 15 patents are compound- and composition-related, having expiration dates from 2021 to 2025; one patent is synthesis-method related, having an expiration date in 2022; one patent is proteomics methodology-related having an expiration date in 2022; and three patents are screening methodology-related, having expiration dates from 2022 to 2023. Subject to possible patent term extension, the entitlement for which and the term of which we cannot predict, patent protection in the United States covering XP13512, our product candidate that is a Transported Prodrug of gabapentin, will expire no earlier than 2023. We believe that in all countries in which we hold or have licensed rights to patents or patent applications related to XP13512, the composition-of-matter patents relating to gabapentin have expired. For XP19986, our product candidate that is a Transported Prodrug of R-baclofen, one U.S. patent has issued that will expire no earlier than 2025. In addition, four U.S. and 36 non-U.S. patent applications are pending. Although third parties may challenge our rights to, or the scope or validity of, our patents, to date, we have not received any communications from third parties challenging our patents or patent applications covering our product candidates.

     We also rely on trade secrets to protect our technology, especially where we do not believe that patent protection is appropriate or obtainable. However, trade secrets are difficult to protect. Our employees, consultants, contractors, outside scientific collaborators and other advisors may unintentionally or willfully disclose our confidential information to competitors. Enforcing a claim that a third party illegally obtained and is using our trade secrets is expensive and time-consuming, and the outcome is unpredictable. Failure to obtain or maintain trade secret protection could adversely affect our competitive business position.

     Our research and development collaborators may have rights to publish data and other information in which we have rights. In addition, we sometimes engage individuals or entities to conduct research that may be relevant to our business. The ability of these individuals or entities to publish or otherwise publicly disclose data and other information generated during the course of their research is subject to certain contractual limitations. In most cases, these individuals or entities are, at the least, precluded from publicly disclosing our confidential information and are only allowed to disclose other data or information generated during the course of the research after we have been afforded an opportunity to consider whether patent and/or other proprietary protection should be sought. If we do not apply for patent protection prior to such publication or if we cannot otherwise maintain the confidentiality of our technology and other confidential information, then our ability to receive patent protection or protect our proprietary information may be jeopardized.

     Third-party claims of intellectual property infringement would require us to spend significant time and money and could prevent us from developing or commercializing our products.

     Our commercial success depends in part on not infringing the patents and proprietary rights of other parties and not breaching any licenses that we have entered into with regard to our technologies and products. Because others may have filed, and in the future are likely to file, patent applications covering products or other technologies of interest to us that are similar or identical to ours, patent applications or issued patents of others may have priority over our patent applications or issued patents. For example, we are aware of a third party patent application relating to prodrugs of gabapentin that, if it issues, if it is determined to be valid and if it is construed to cover XP13512, could affect the development and commercialization of XP13512. Additionally, we are aware of third-party patents relating to the use of baclofen in the treatment of gastroesophageal reflux disease, or GERD. If the patents are determined to be valid and construed to cover XP19986, the development and commercialization of XP19986 could be affected. With respect to the claims contained in these patent applications and patents, we believe that our activities do not infringe the patents at issue and/or that the third-party patent or patent applications are invalid. However, it is possible that a judge or jury will disagree with our conclusions regarding non-infringement and/or invalidity, and we could incur substantial costs in litigation if we are required to defend against patent suits brought by third parties or if we initiate these suits. Any legal action against our collaborators or us claiming damages and seeking to enjoin commercial activities relating to the affected products and processes could, in addition to subjecting us to potential liability for damages, require our collaborators or us to obtain a license to continue to manufacture or market the affected products and processes. Licenses required under any of these patents may not be available on commercially acceptable terms, if at all. Failure to

obtain such licenses could materially and adversely affect our ability to develop, commercialize and sell our product candidates. We believe that there may continue to be significant litigation in the biotechnology and pharmaceutical industry regarding patent and other intellectual property rights. If we become involved in litigation, it could consume a substantial portion of our management and financial resources and we may not prevail in any such litigation.

     Furthermore, our commercial success will depend, in part, on our ability to continue to conduct research to identify additional product candidates in current indications of interest or opportunities in other indications. Some of these activities may involve the use of genes, gene products, screening technologies and other research tools that are covered by third-party patents. Court decisions have indicated that the exemption from patent infringement afforded by 35 U.S.C. §271(e)(1) does not encompass all research and development activities associated with product development. In some instances, we may be required to obtain licenses to such third-party patents to conduct our research and development activities, including activities that may have already occurred. It is not known whether any license required under any of these patents would be made available on commercially acceptable terms, if at all. Failure to obtain such licenses could materially and adversely affect our ability to maintain a pipeline of potential product candidates and to bring new products to market. If we are required to defend against patent suits brought by third parties relating to third-party patents that may be relevant to our research activities, or if we initiate such suits, we could incur substantial costs in litigation. Moreover, an adverse result from any legal action in which we are involved could subject us to damages and/or prevent us from conducting some of our research and development activities.

     If third parties do not manufacture our product candidates in sufficient quantities or at an acceptable cost, clinical development and commercialization of our product candidates would be delayed.*

     We presently do not have on hand sufficient quantities of our product candidates to complete clinical trials of either XP13512 or XP19986. We do not currently own or operate manufacturing facilities for the production of clinical or commercial quantities of any of our product candidates. To date, we have relied on a small number of third-party compound manufacturers and active pharmaceutical ingredient, or API, formulators for the production of clinical and commercial quantities of our product candidates. Under the terms of our collaboration with GSK, we will transition the manufacturing of XP13512 to GSK, and GSK will be solely responsible for the manufacture of XP13512 to support its development and commercialization within the licensed territories. However, we will continue to be responsible for providing Astellas both clinical and commercial supplies of XP13512. Thus, we expect to continue to rely on a small number of third-party manufacturers to meet our clinical requirements of XP13512 during the GSK transition period, to meet our clinical and commercial supply obligations to Astellas for XP13512 and to meet our preclinical and clinical requirements of our other potential products and for any related commercial needs. We do not have commercial supply agreements with any of these third parties, and our agreements with these parties are generally terminable at will by either party at any time. If, for any reason, these third parties are unable or unwilling to perform under our agreements or enter into new agreements, we may not be able to locate alternative manufacturers or formulators or enter into favorable agreements with them. Any inability to acquire sufficient quantities of our product candidates in a timely manner from these third parties could delay clinical trials and prevent us or our partners from developing and commercializing our product candidates in a cost-effective manner or on a timely basis. We purchase substantial amounts of gabapentin, which is used to make XP13512, from Teva Pharmaceutical Industries, Ltd. pursuant to purchase orders issued from time to time. Teva’s sale of gabapentin is the subject of ongoing litigation brought by Pfizer Inc alleging infringement of a patent held by Pfizer. In July 2006, the Federal District Court ruled in favor of the generic gabapentin makers, including Teva, and Pfizer has appealed this ruling. In the event that Teva decides not to sell gabapentin to us, or decides to sell gabapentin to us at a price that is not commercially attractive, or, as a result of this litigation, ceases producing gabapentin, we would not be able to manufacture XP13512 until a qualified alternative supplier is identified. This could delay the development of, and impair our or our collaborative partners’ ability to commercialize, this product candidate.

     We currently rely on Lonza Ltd. as the single source supplier of our current worldwide requirements of XP13512 API. We have agreed to purchase XP13512 API from Lonza under a manufacturing services and product supply agreement. In the event that Lonza terminates the agreement in response to a breach by us, we would not be able to manufacture the API until a qualified alternative supplier is identified. This could delay the development of, and impair the ability of us or our partners to commercialize, this product candidate. In addition, our current agreement with Lonza does not provide for the entire supply of API that we require to complete all of our planned clinical trials or for full-scale commercialization. However, the manufacturing services and product supply agreement obligates the parties to negotiate in good faith on the terms and conditions for Lonza to supply some or all of our total requirements for the commercial supply of XP13512 API. In the event that the parties cannot agree to the terms and conditions for Lonza to provide some or all of our API commercial supply needs, we would not be able to manufacture API until a qualified alternative supplier is identified, which could also delay the development of, and impair the ability of us or our partners to commercialize, this product candidate. Unless earlier terminated, this agreement expires in July 2007.

     In addition, we currently rely on Patheon Pharmaceuticals, Inc. as our single source supplier for XP13512 formulated in sustained-release tablets for clinical trials at specified transfer prices under a quotation agreed upon by the parties that forms a part of a master services agreement. In the event that Patheon terminates the agreement under specified circumstances, we would not be able to manufacture XP13512 sustained-release tablets until a qualified alternative supplier is identified. This could delay the development of, and impair the ability of us or our partners to commercialize, XP13512.

     We currently rely on Heumann Pharma GmbH as our single source supplier of R-baclofen, the active agent used to make XP19986, under purchase orders issued from time to time. We are aware of two alternative suppliers of R-baclofen. If we were unable to qualify an alternative supplier of R-baclofen, this could delay the development of, and impair our ability to commercialize, this product candidate.

     We currently rely on Xcelience, LLC as our single source supplier for XP19986 formulated in sustained-release tablets for clinical trials at specified transfer prices under quotation agreed upon by the parties as a part of a master services agreement. In the event that Xcelience terminates the agreement under specified circumstances, we would not be able to manufacture XP19986 sustained-release tablets until a qualified alternative supplier is identified. This could delay the development of, and impair our ability to commercialize, XP19986.

     We have relied on Lonza as the single source supplier of our current worldwide requirements of XP19986 in API form through our initial Phase 2a clinical trial under a manufacturing services and product supply agreement. Our current agreement with Lonza does not provide for the entire supply of the API necessary for additional Phase 2 and Phase 3 clinical trials or for full-scale commercialization. In the event that the parties cannot agree to the terms and conditions for Lonza to provide some or all of our API clinical and commercial supply needs, we would not be able to manufacture API until a qualified alternative supplier is identified, which could also delay the development of, and impair our ability to commercialize, this product candidate.

     If we are required to obtain alternate third-party manufacturers, it could delay or prevent the clinical development and commercialization of our product candidates.

     We may not be able to maintain or renew our existing or any other third-party manufacturing arrangements on acceptable terms, if at all. If we are unable to continue relationships with Teva, Lonza or Patheon for XP13512, or Heumann, Lonza or Xcelience for XP19986, or to do so at an acceptable cost, or if these suppliers fail to meet our requirements for these product candidates for any reason, we would be required to obtain alternative suppliers. Any inability to obtain qualified alternative suppliers, including an inability to obtain, or delay in obtaining, approval of an alternative supplier from the FDA, would delay or prevent the clinical development and commercialization of these product candidates, and could impact our ability to meet our supply obligations to Astellas.

     Prior to the commencement of our Phase 3 clinical trials, the formulation of XP13512 that had been tested in humans had been produced by entities other than Patheon. We completed an additional Phase 1 clinical trial to assess the safety, tolerability and pharmacokinetics of single doses of XP13512 manufactured by Patheon. This clinical trial utilized a sustained-release formulation of XP13512 produced at a larger scale. These tablets are similar in characteristics compared to the sustained-release formulation used in previous trials. We conducted this additional Phase 1 single-dose, crossover clinical trial in 12 healthy volunteers at one site. Results from this clinical trial suggest that the new, larger-scale, sustained-release formulation of XP13512 produces blood levels of gabapentin that are similar to the sustained-release formulation used in the previous clinical trials. There can be no assurance that additional clinical trials with the larger-scale, sustained-release tablet formulation will replicate results from our earlier clinical trials. The failure to replicate these earlier clinical trials could delay our clinical development timelines.

     Any failure or delay in developing or manufacturing, or obtaining a qualified commercial supplier of, a new sustained-release tablet formulation of XP19986 could delay the clinical development and commercialization of this product candidate.*

     Cardinal Health PTS, LLC provided our requirements of XP19986 for our Phase 1 and Phase 2a clinical trials in the form of capsules containing controlled-release beads. However, we have developed new sustained-release tablet formulations of XP19986 to replace the Cardinal Health capsules and have conducted clinical trials with these new tablet formulations. To be successful, the sustained-release tablet formulations will need to continue to demonstrate acceptable safety and efficacy, and there can be no assurance that clinical trials with the sustained-release tablet formulations will replicate results from our earlier clinical trials with the capsule formulation. The failure to replicate these earlier clinical trials would delay our clinical development timelines. We have engaged Xcelience as a third-party manufacturer for the new sustained-release tablet formulations. Any inability to obtain a qualified commercial supplier, including an inability to obtain, or delay in obtaining, approval of a supplier from the FDA, would delay or prevent the clinical development and commercialization of this product candidate. We currently ship XP19986 using refrigerated containers. We anticipate that manufacturing improvements we will make will alleviate the need to ship this product candidate for commercial sale using refrigerated containers. If we are unable to achieve these manufacturing improvements, we may incur additional expenses and delays that could impair our ability to generate product revenue.

     Use of third-party manufacturers may increase the risk that we or our partners will not have adequate supplies of our product candidates.

     Our current reliance, and our and our partners’ anticipated future reliance, on third-party manufacturers will expose us and our partners to risks that could delay or prevent the initiation or completion of clinical trials by us or our partners, the submission of applications for regulatory approvals, the approval of our products by the FDA or foreign regulatory authorities or the commercialization of our products or could result in higher costs or lost product revenues. In particular, our contract manufacturers:

	•		could encounter difficulties in achieving volume production, quality control and quality assurance or suffer shortages of qualified personnel, which could result in their inability to manufacture sufficient quantities of drugs to meet clinical schedules or to commercialize our product candidates;
	•		could terminate or choose not to renew manufacturing agreements, based on their own business priorities, at a time that is costly or inconvenient for us;
	•		could fail to establish and follow FDA-mandated current good manufacturing practices, or cGMPs, which are required for FDA approval of our product candidates, or fail to document their adherence to cGMPs, either of which could lead to significant delays in the availability of material for clinical study and delay or prevent marketing approval for our product candidates;
	•		could encounter financial difficulties that would interfere with their obligations to supply our product candidates; and
	•		could breach, or fail to perform as agreed under, manufacturing agreements.

     As an example, one of our third-party manufacturers previously released financial results indicating that their earnings were adversely affected due to certain circumstances at one of its manufacturing operations, which, in turn, adversely affected financial covenants of certain loan facilities. In addition, they subsequently announced that their board of directors had established a special committee and engaged financial advisors to evaluate strategic and financial alternatives for the company. If such financial difficulties interfere with their ability to satisfy their contractual obligations to supply our product candidates, there could be a delay in commencing or completing our or our collaborative partners’ clinical trials, which could also delay the development of, and impair our or our partners’ ability to commercialize, our product candidates.

     We use Patheon to manufacture XP13512 sustained-release tablets that we utilize for our clinical trials and the clinical trials of Astellas. Patheon continues to perform formulation development work to achieve the commercial image for XP13512, including color coating and brand marking for the tablets that would be sold following regulatory approval, if obtained. Patheon may not be able to manufacture this product candidate using our desired commercial image, which would delay or prevent the commercialization of XP13512 by Astellas and could impact our ability to meet our supply obligations to Astellas.

     If we are not able to obtain adequate supplies of our product candidates, it will be more difficult to develop our product candidates and compete effectively. Our product candidates and any products that we may develop may compete with other product candidates and products for access to manufacturing facilities. For example, gabapentin is also marketed as generic gabapentin by Teva, one of our third-party manufacturers.

     In addition, the manufacturing facilities of Heumann, Lonza and Teva are located outside of the United States. This may give rise to difficulties in importing our product candidates or their components into the United States or other countries as a result of, among other things, regulatory agency import inspections, incomplete or inaccurate import documentation or defective packaging.

     Safety issues with the parent drugs or other components of our product candidates, or with approved products of third parties that are similar to our product candidates, could give rise to delays in the regulatory approval process, restrictions on labeling or product withdrawal.

     Discovery of previously unknown problems with an approved product may result in restrictions on its permissible uses, including withdrawal of the medicine from the market. The FDA approved gabapentin, the parent drug for our XP13512 product candidate, in 1993, and, to date, it has been used in at least 12 million patients. Baclofen, the R-isomer of which is the parent drug for our XP19986 product candidate, has been used since 1977. The FDA has not approved the R-isomer of baclofen for use in humans. Although gabapentin and baclofen have been used successfully in patients for many years, newly observed toxicities, or worsening of known toxicities, in patients receiving gabapentin or baclofen could result in increased regulatory scrutiny of XP13512 or XP19986, respectively.

     Our product candidates are engineered to be broken down by the body’s natural metabolic processes and to release the parent drug and other metabolic substances. While these breakdown products are generally regarded as safe, it is possible that there could be unexpected toxicity associated with these breakdown products that will cause either or both of XP13512 and XP19986 to be poorly tolerated by, or toxic to, humans. Any unexpected toxicity of, or suboptimal tolerance to, our Transported Prodrugs would delay or prevent commercialization of these product candidates.

     Additionally, problems with approved products marketed by third parties that utilize the same therapeutic target as the parent drug of our product candidates could adversely affect the development of our product candidates. For example, the product withdrawals of Vioxx by Merck & Co., Inc. and Bextra from Pfizer in 2005 due to safety issues has caused other drugs that have the same therapeutic target, such as Celebrex from Pfizer, to receive additional scrutiny from regulatory authorities. If either gabapentin or pregabalin, a drug from Pfizer that is marketed as Lyrica, encounters unexpected toxicity problems in humans, the FDA may delay or prevent the regulatory approval of XP13512 since it is a member of the same class of drugs and shares the same therapeutic target as gabapentin and pregabalin. In 2005, the FDA requested that all makers of epilepsy drugs, including Neurontin, analyze their clinical trial data to determine whether these drugs increase the risk of suicide in patients. Finally, if the FDA determines that a drug may present a risk of substance abuse, it can recommend to the DEA that the drug be scheduled under the Controlled Substances Act. While gabapentin is not a scheduled drug at the present time, pregabalin has been scheduled as a controlled substance. Since pregabalin is a scheduled drug, it is possible that the FDA may require additional testing of XP13512, the results of which could lead the FDA to conclude that XP13512 should be scheduled as well. Scheduled substances are subject to DEA regulations relating to manufacturing, storage, distribution and physician prescription procedures, and the DEA regulates the amount of a scheduled substance that is available for clinical trials and commercial distribution. Accordingly, any scheduling action that the FDA or DEA may take with respect to XP13512 may delay its clinical trial and approval process. Any failure or delay in commencing or completing clinical trials or obtaining regulatory approvals for our product candidates would delay commercialization of our product candidates and severely harm our business and financial condition.

     We may not be successful in our efforts to identify or discover additional Transported Prodrug candidates.

     An important element of our strategy is to identify, develop and commercialize Transported Prodrugs that improve upon the absorption, distribution and/or metabolism of drugs that have already received regulatory approval. Other than XP13512 and XP19986, all of our research and development programs are at a preclinical stage. Research programs to identify new product candidates require substantial technical, financial and human resources. These research programs may initially show promise in identifying potential product candidates, yet fail to yield product candidates for clinical development for a number of reasons, including:

	•		the research methodology used may not be successful in identifying potential product candidates; or
	•		potential product candidates may, on further study, be shown to have inadequate efficacy, harmful side effects, suboptimal pharmaceutical profile or other characteristics suggesting that they are unlikely to be effective products.

     If we are unable to develop suitable product candidates through internal research programs or otherwise, we will not be able to increase our revenues in future periods, which could result in significant harm to our financial position and adversely impact our stock price.

     Our product candidates will remain subject to ongoing regulatory review, even if they receive marketing approval. If we or our collaborative partners fail to comply with continuing regulations, these approvals could be rescinded and the sale of our products could be suspended.

     Even if we or our collaborative partners receive regulatory approval to market a particular product candidate, the approval could be conditioned on conducting additional, costly, post-approval studies or could limit the indicated uses included in the labeling. Moreover, the product may later cause adverse effects that limit or prevent its widespread use, force us or our collaborative partners to withdraw it from the market or impede or delay our or our collaborative partners’ ability to obtain regulatory approvals in additional countries. In addition, the manufacturer of the product and its facilities will continue to be subject to FDA review and periodic inspections to ensure adherence to applicable regulations. After receiving marketing approval, the manufacturing, labeling, packaging, adverse event reporting, storage, advertising, promotion and record keeping related to the product will remain subject to extensive regulatory requirements.

     If we or our collaborative partners fail to comply with the regulatory requirements of the FDA and other applicable U.S. and foreign regulatory authorities or previously unknown problems with our products, manufacturers or manufacturing processes are discovered, we and our partners could be subject to administrative or judicially imposed sanctions, including:

	•		restrictions on the products, manufacturers or manufacturing processes;
	•		warning letters;
	•		civil or criminal penalties or fines;
	•		injunctions;
	•		product seizures, detentions or import bans;
	•		voluntary or mandatory product recalls and publicity requirements;
	•		suspension or withdrawal of regulatory approvals;
	•		total or partial suspension of production; and
	•		refusal to approve pending applications for marketing approval of new drugs or supplements to approved applications.

     Because we have a number of product candidates and are considering a variety of target indications, we may expend our limited resources to pursue a particular candidate or indication and fail to capitalize on candidates or indications that may be more profitable or for which there is a greater likelihood of success.*

     Because we have limited financial and managerial resources, we must focus on research programs and product candidates for the specific indications that we believe are the most promising. As a result, we may forego or delay pursuit of opportunities with other product candidates or other indications that later prove to have greater commercial potential. Our resource allocation decisions may cause us to fail to capitalize on viable commercial products or profitable market opportunities. In addition, we may spend valuable time and managerial and financial

resources on research programs and product candidates for specific indications that ultimately do not yield any commercially viable products. If we do not accurately evaluate the commercial potential or target market for a particular product candidate, we may relinquish valuable rights to that product candidate through collaboration, licensing or other royalty arrangements in situations where it would have been more advantageous for us to retain sole rights to development and commercialization.

     The commercial success of any products that we or our partners may develop will depend upon the degree of market acceptance among physicians, patients, healthcare payors and the medical community.

     Any products that result from our product candidates may not gain market acceptance among physicians, patients, healthcare payors and the medical community. If these products do not achieve an adequate level of acceptance, we may not generate material product revenues and we may not become profitable. The degree of market acceptance of any products resulting from our product candidates will depend on a number of factors, including:

	•		demonstration of efficacy and safety in clinical trials;
	•		the prevalence and severity of any side effects;
	•		potential or perceived advantages over alternative treatments;
	•		perceptions about the relationship or similarity between our product candidates and the parent drug upon which each Transported Prodrug candidate was based;
	•		the timing of market entry relative to competitive treatments;
	•		the ability to offer product candidates for sale at competitive prices;
	•		relative convenience and ease of administration;
	•		the strength of marketing and distribution support;
	•		sufficient third-party coverage or reimbursement; and
	•		the product labeling or product insert required by the FDA or regulatory authorities in other countries.

     If we are unable to establish sales and marketing capabilities or enter into additional agreements with third parties to market and sell our product candidates, we may be unable to generate product revenues.*

     We do not have a sales and marketing organization and have no experience in the sales, marketing and distribution of pharmaceutical products. There are risks involved with establishing our own sales and marketing capabilities, as well as entering into arrangements with third parties to perform these services. Developing an internal sales force is expensive and time-consuming. On the other hand, if we enter into arrangements with third parties to perform sales, marketing and distribution services, as we have for XP13512, our product revenues will be lower than if we market and sell any products that we develop ourselves.

     Under the terms of our collaboration with GSK, we are entitled to a percentage of sales of XP13512 in the GSK territory for a specified period of time, unless we elect the option to co-promote XP13512 in the United States. In the event that we elect the co-promotion option for XP13512, we would share marketing and commercialization costs and would be entitled to a share of operating profits from sales of XP13512 in the United States, as well as payments on details we perform on Requip CR and Requip XL 24-Hour, GSK’s development-stage product candidates for RLS and Parkinson’s disease, respectively, in the United States. Subject to approval from the FDA of an NDA for XP13512, we would co-promote XP13512 in the United States to those same prescribers. If we elect the co-promotion option for XP13512, we plan to establish our own specialty sales force to sell, market and distribute our products.

     Factors that may inhibit our efforts to commercialize our products include:

	•		our inability to recruit and retain adequate numbers of effective sales and marketing personnel;
	•		the inability of sales personnel to obtain access to or persuade adequate numbers of physicians to prescribe our products;
	•		the lack of complementary products to be offered by sales personnel, which may put us at a competitive disadvantage relative to companies with more extensive product lines; and
	•		unforeseen costs and expenses associated with creating an independent sales and marketing organization.

     Because of the numerous risks and uncertainties involved with establishing our own sales and marketing capabilities, we are unable to predict when we will establish our own sales and marketing capabilities. If we are not successful in recruiting sales and marketing personnel or in building a sales and marketing infrastructure, we will have difficulty commercializing our product candidates, which would adversely affect our business and financial condition.

     Our ability to generate revenue from any products that we may develop will depend on reimbursement and drug pricing policies and regulations.

     Many patients may be unable to pay for any products that we or our collaborative partners may develop. In the United States, many patients will rely on Medicare, Medicaid, private health insurers and other third-party payors to pay for their medical needs. Our and our partners’ ability to achieve acceptable levels of reimbursement for drug treatments by governmental authorities, private health insurers and other organizations will have an effect on our and our partners’ ability to successfully commercialize, and attract additional collaborators to invest in the development of, our product candidates. We cannot be sure that reimbursement in the United States, Europe or elsewhere will be available for any products that we or our partners may develop, and any reimbursement that may become available may be decreased or eliminated in the future. Third-party payors increasingly are challenging prices charged for medical products and services, and many third-party payors may refuse to provide reimbursement for particular drugs when an equivalent generic drug is available. Although we believe any products that may result from our product candidates will represent an improvement over the parent drugs upon which they are based and be considered unique and not subject to substitution by a generic parent drug, it is possible that a third-party payor may consider our product candidate and the generic parent drug as equivalents and only offer to reimburse patients for the generic drug. Even if we show improved efficacy or improved convenience of administration with our product candidate, pricing of the existing parent drug may limit the amount we will be able to charge for our product candidate. If reimbursement is not available or is available only at limited levels, we or our partners may not be able to successfully commercialize our product candidates, and may not be able to obtain a satisfactory financial return on such products.

     The trend toward managed healthcare in the United States and the changes in health insurance programs, as well as legislative proposals to reform healthcare or reduce government insurance programs, may result in lower prices for pharmaceutical products, including any products that may result from our product candidates. In addition, any future regulatory changes regarding the healthcare industry or third-party coverage and reimbursement may affect demand for any products that we may develop and could harm our sales and profitability.

     In December 2003, the Medicare Prescription Drug Improvement and Modernization Act of 2003, or the 2003 Medicare Act, was enacted. Under this legislation, Medicare beneficiaries are eligible to obtain a Medicare endorsed, drug-discount card from a pharmacy benefit manager, managed care organization or other private sector provider. Beginning on January 1, 2006, Medicare beneficiaries were eligible to obtain subsidized prescription drug coverage from a private sector provider. It remains difficult to predict the impact of the 2003 Medicare Act on pharmaceutical companies. Usage of pharmaceuticals may increase as the result of the expanded access to medicines afforded by the partial reimbursement under Medicare. Such potential sales increases, however, may be offset by increased pricing pressures due to the enhanced purchasing power of the private sector providers that will negotiate on behalf of Medicare beneficiaries.

     If our competitors are able to develop and market products that are more effective, safer or less costly than any products that we may develop, our commercial opportunity will be reduced or eliminated.

     We face competition from established pharmaceutical and biotechnology companies, as well as from academic institutions, government agencies and private and public research institutions. Our commercial opportunity will be reduced or eliminated if our competitors develop and commercialize products that are safer, more effective, have fewer side effects or are less expensive than any products that we may develop. In addition, significant delays in the development of our product candidates could allow our competitors to bring products to market before us and impair our ability to commercialize our product candidates.

     We estimate that we have at least five competitors in the neuropathic pain and RLS therapeutic areas, including GSK, Eli Lilly and Company and Pfizer. Competition for XP13512 could include: approved drugs that act on the same target as XP13512, such as pregabalin, Neurontin and generic gabapentin; anti-Parkinson’s disease products and product candidates, such as ropinirole from GSK, which is approved for the treatment of moderate-to-severe RLS, pramipexole from Boehringer Ingelheim GmbH, which is approved for the treatment of moderate-to-severe RLS and the rotigotine patch from Schwarz Pharma AG, which has recently announced Phase 3 data for the treatment of moderate-to-severe RLS; serotonin norepinephrine inhibitors, such as duloxetine from Eli Lilly, which is approved for the management of painful diabetic neuropathy; and gabapentin GR from Depomed, Inc., which is in a Phase 3 trial for post-herpetic neuralgia, or PHN. We are aware that generic gabapentin is marketed by Alpharma Inc., Pfizer, Teva and IVAX Corp, among others, and that it is prescribed off-label to treat a variety of conditions. We estimate that XP19986 could have several generic drug competitors in the spasticity area. There are several drugs approved for the treatment of spasticity, such as racemic baclofen, diazepam, dantrolene sodium and tizanidine, and many therapies in development, such as Fampridine-SR from Acorda Therapeutics, Inc., that could compete with XP19986. We estimate that we have at least three competitors in the GERD therapeutic area, including AstraZeneca, Wyeth and TAP Pharmaceutical Products Inc. In addition, there may be other compounds of which we are not aware that are at an earlier stage of development and may compete with our product candidates. If any of those compounds are successfully developed and approved, they could compete directly with our product candidates.

     Many of our competitors have significantly greater financial resources and expertise in research and development, manufacturing, preclinical testing, conducting clinical trials, obtaining regulatory approvals and marketing approved products than we do. Established pharmaceutical companies may invest heavily to quickly discover and develop novel compounds that could make our product candidates obsolete. Smaller or early-stage companies may also prove to be significant competitors, particularly through collaborative arrangements with large and established companies. In addition, these third parties compete with us in recruiting and retaining qualified scientific and management personnel, establishing clinical trial sites and patient registration for clinical trials, as well as in acquiring technologies and technology licenses complementary to our programs or advantageous to our business. Accordingly, our competitors may succeed in obtaining patent protection, receiving FDA approval or discovering, developing and commercializing medicines before we do. We are also aware of other companies that may currently be engaged in the discovery of medicines that will compete with the product candidates that we are developing. In addition, in the markets that we are targeting, we expect to compete against current market-leading medicines. If we are not able to compete effectively against our current and future competitors, our business will not grow and our financial condition will suffer.

     Off-label sale or use of generic gabapentin products could decrease sales of XP13512 and could lead to pricing pressure if such products become available at competitive prices and in dosages that are appropriate for the indications for which we or our collaborative partners are developing XP13512.

     Physicians are permitted to prescribe legally available drugs for uses that are not described in the drug’s labeling and that differ from those uses tested and approved by the FDA. Such off-label uses are common across medical specialties. Various products are currently sold and used off-label for some of the diseases and conditions that we or our partners are targeting, and a number of companies are, or may be, developing new treatments that may be used off-label. The occurrence of such off-label uses could significantly reduce our or our partners’ ability to market and sell any products that we or our partners may develop.

     We believe that in all countries in which we hold or have licensed rights to patents or patent applications related to XP13512, the composition-of-matter patents relating to gabapentin have expired. Off-label prescriptions written for gabapentin could adversely affect our ability to generate revenue from the sale of XP13512, if approved for commercial sale. This could result in reduced sales and pricing pressure on XP13512, if approved, which in turn would reduce our ability to generate revenue and have a negative impact on our results of operations.

     If we fail to attract and keep senior management and key scientific personnel, we may be unable to successfully develop or commercialize our product candidates.

     Our success depends on our continued ability to attract, retain and motivate highly qualified management, clinical and scientific personnel and on our ability to develop and maintain important relationships with leading clinicians. If we are not able to retain Drs. Ronald Barrett, Kenneth Cundy, William Dower, Mark Gallop and Pierre Trân, we may not be able to successfully develop or commercialize our product candidates. Competition for experienced scientists may limit our ability to hire and retain highly qualified personnel on acceptable terms. In addition, none of our employees have employment commitments for any fixed period of time and could leave our employment at will. We do not carry “key person” insurance covering members of senior management or key scientific personnel. If we fail to identify, attract and retain qualified personnel, we may be unable to continue our development and commercialization activities.

     We will need to hire additional employees in order to commercialize our product candidates. Any inability to manage future growth could harm our ability to commercialize our product candidates, increase our costs and adversely impact our ability to compete effectively.

     In order to commercialize our product candidates, we will need to expand the number of our managerial, operational, financial and other employees. We currently anticipate that we will need at least 250 additional employees by the time that XP13512 or XP19986 is initially commercialized, including at least 80 sales representatives. Because the projected timeframe of hiring these additional employees depends on the development status of our product candidates and because of the numerous risks and uncertainties associated with drug development, we are unable to project when we will hire these additional employees. While to date we have not experienced difficulties in recruiting, hiring and retaining qualified individuals, the competition for qualified personnel in the pharmaceutical and biotechnology field is intense.

     Future growth will impose significant added responsibilities on members of management, including the need to identify, recruit, maintain and integrate additional employees. Our future financial performance and our ability to commercialize our product candidates and compete effectively will depend, in part, on our ability to manage any future growth effectively.

     If product liability lawsuits are brought against us, we will incur substantial liabilities and may be required to limit commercialization of any products that we may develop.

     We face an inherent risk of product liability exposure related to the testing of our product candidates in human clinical trials and will face an even greater risk if we commercially sell any products that we may develop. If we cannot successfully defend ourselves against claims that our product candidates or products that we may develop caused injuries, we will incur substantial liabilities. Regardless of merit or eventual outcome, liability claims may result in:

	•		decreased demand for any product candidates or products that we may develop;
	•		injury to our reputation;
	•		withdrawal of clinical trial participants;
	•		costs to defend the related litigation;
	•		substantial monetary awards to clinical trial participants or patients;
	•		loss of revenue; and
	•		the inability to commercialize any products that we may develop.

     We have product liability insurance that covers our clinical trials up to a $5.0 million annual aggregate limit. We intend to expand our insurance coverage to include the sale of commercial products if marketing approval is obtained for any products that we may develop. Insurance coverage is increasingly expensive, and we may not be able to maintain insurance coverage at a reasonable cost and we may not be able to obtain insurance coverage that will be adequate to satisfy any liability that may arise.

     If we use biological and hazardous materials in a manner that causes contamination, injury or violates laws, we may be liable for damages.

     Our research and development activities involve the use of potentially harmful biological materials as well as hazardous materials, chemicals and various radioactive compounds. We cannot completely eliminate the risk of accidental contamination or injury from the use, storage, handling or disposal of these materials. In the event of contamination or injury, we could be held liable for damages that result, and any liability could exceed our resources. We, the third parties that conduct clinical trials on our behalf and the third parties that manufacture our product candidates are subject to federal, state and local laws and regulations governing the use, storage, handling and disposal of these materials and waste products. The cost of compliance with these laws and regulations could be significant. The failure to comply with these laws and regulations could result in significant fines and work stoppages and may harm our business.

     Our facility is located in California’s Silicon Valley, in an area with a long history of industrial activity and use of hazardous substances, including chlorinated solvents. Environmental studies conducted prior to our leasing of the site found levels of metals and volatile organic compounds in the soils and groundwater at our site. While these constituents of concern predated our occupancy, certain environmental laws, including the U.S. Comprehensive, Environmental Response, Compensation and Liability Act of 1980, impose strict, joint and several liability on current operators of real property for the cost of removal or remediation of hazardous substances. These laws often impose liability even if the owner or operator did not know of, or was not responsible for, the release of such hazardous substances. As a result, while we have not been, we cannot rule out the possibility that we could in the future be held liable for costs to address contamination at the property beneath our facility, which costs could be material.

     Our facility is located near known earthquake fault zones, and the occurrence of an earthquake, extremist attack or other catastrophic disaster could cause damage to our facilities and equipment, which could require us to cease or curtail operations.

     Our facility is located near known earthquake fault zones and, therefore, is vulnerable to damage from earthquakes. In October 1989, a major earthquake struck this area and caused significant property damage and a number of fatalities. We are also vulnerable to damage from other types of disasters, including power loss, attacks from extremist organizations, fire, floods and similar events. If any disaster were to occur, our ability to operate our business could be seriously impaired. In addition, the unique nature of our research activities and of much of our equipment could make it difficult for us to recover from this type of disaster. We currently may not have adequate insurance to cover our losses resulting from disasters or other similar significant business interruptions, and we do not plan to purchase additional insurance to cover such losses due to the cost of obtaining such coverage. Any significant losses that are not recoverable under our insurance policies could seriously impair our business and financial condition.

Risks Related to Ownership of our Common Stock

     Our stock price is volatile, and purchasers of our common stock could incur substantial losses.

     The market prices for securities of biopharmaceutical companies in general have been highly volatile. The market price of our common stock may be influenced by many factors, including:

	•		adverse results or delays in our clinical trials;
	•		the timing of achievement of our clinical, regulatory, partnering and other milestones, such as the commencement of clinical development, the completion of a clinical trial, the receipt of regulatory approval or the establishment of commercial partnerships for one or more of our product candidates;
	•		announcement of FDA approval or non-approval of our product candidates or delays in the FDA review process;
	•		actions taken by regulatory agencies with respect to our product candidates, our clinical trials or our sales and marketing activities;
	•		the commercial success of any of our products approved by the FDA or its foreign counterparts;

	•		regulatory developments in the United States and foreign countries;
	•		changes in the structure of healthcare payment systems;
	•		any intellectual property infringement lawsuit involving us;
	•		announcements of technological innovations or new products by us or our competitors;
	•		market conditions for the biotechnology or pharmaceutical industries in general;
	•		changes in financial estimates or recommendations by securities analysts;
	•		sales of large blocks of our common stock;
	•		sales of our common stock by our executive officers, directors and significant stockholders;
	•		restatements of our financial results and/or material weaknesses in our internal controls; and
	•		the loss of any of our key scientific or management personnel.

     The stock markets in general, and the markets for biotechnology stocks in particular, have experienced extreme volatility that has often been unrelated to the operating performance of particular companies. These broad market fluctuations may adversely affect the trading price of our common stock. In the past, class action litigation has often been instituted against companies whose securities have experienced periods of volatility in market price. Any such litigation brought against us could result in substantial costs, which would hurt our financial condition and results of operations, divert management’s attention and resources, and possibly delay our clinical trials or commercialization efforts.

     Failure to maintain effective internal controls in accordance with Section 404 of the Sarbanes-Oxley Act of 2002 could have a material adverse effect on our stock price.

     Section 404 of the Sarbanes-Oxley Act of 2002 and the related rules and regulations of the SEC require annual management assessments of the effectiveness of our internal control over financial reporting and a report by our independent registered public accounting firm attesting to, and reporting on, these assessments. If we fail to maintain the adequacy of our internal control over financial reporting, as such standards are modified, supplemented or amended from time to time, we may not be able to ensure that we can conclude on an ongoing basis that we have effective internal control over financial reporting in accordance with Section 404 of the Sarbanes-Oxley Act of 2002 and the related rules and regulations of the SEC. If we cannot favorably assess, or our independent registered public accounting firm is unable to provide an unqualified attestation report on, the effectiveness of our internal control over financial reporting, investor confidence in the reliability of our financial reports may be adversely affected, which could have a material adverse effect on our stock price.

Fluctuations in our operating results could cause our stock price to decline.

     The following factors are likely to result in fluctuations of our operating results from quarter to quarter and year to year:

	•		adverse results or delays in our clinical trials;
	•		the timing and achievement of our clinical, regulatory, partnering and other milestones, such as the commencement of clinical development, the completion of a clinical trial, the receipt of regulatory approval or the establishment of a commercial partnership for one or more of our product candidates;
	•		announcement of FDA approval or non-approval of our product candidates or delays in the FDA review process;
	•		actions taken by regulatory agencies with respect to our product candidates, our clinical trials or our sales and marketing activities;

	•		the commercial success of any of our products approved by the FDA or its foreign counterparts;
	•		regulatory developments in the United States and foreign countries;
	•		changes in the structure of healthcare payment systems;
	•		any intellectual property infringement lawsuit involving us; and
	•		announcements of technological innovations or new products by us or our competitors.

     Due to these fluctuations in our operating results, a period-to-period comparison of our results of operations may not be a good indication of our future performance. In any particular financial period, the actual or anticipated fluctuations could be below the expectations of securities analysts or investors and our stock price could decline.

     Because a small number of existing stockholders own a large percentage of our voting stock, they may be able to exercise significant influence over our affairs, acting in their best interests and not necessarily those of other stockholders.*

     As of April 13, 2007, our executive officers, directors and holders of 5% or more of our outstanding common stock beneficially owned approximately 28.3% of our common stock. The interests of this group of stockholders may not always coincide with our interests or the interests of other stockholders. This concentration of ownership could also have the effect of delaying or preventing a change in our control or otherwise discouraging a potential acquiror from attempting to obtain control of us, which in turn could reduce the price of our common stock.

     Our stockholder rights plan and anti-takeover provisions in our charter documents and under Delaware law could make an acquisition of us, which may be beneficial to our stockholders, more difficult and may prevent attempts by our stockholders to replace or remove our current management.

     Provisions in our amended and restated certificate of incorporation and bylaws may delay or prevent an acquisition of us, a change in our management or other changes that stockholders may consider favorable. These provisions include:

	•		a classified board of directors;
	•		a prohibition on actions by our stockholders by written consent;
	•		the ability of our board of directors to issue preferred stock without stockholder approval, which could be used to make it difficult for a third party to acquire us;
	•		notice requirements for nominations for election to the board of directors; and
	•		limitations on the removal of directors.

     Moreover, we are governed by the provisions of Section 203 of the Delaware General Corporation Law, which prohibits a person who owns in excess of 15% of our outstanding voting stock from merging or combining with us for a period of three years after the date of the transaction in which the person acquired in excess of 15% of our outstanding voting stock, unless the merger or combination is approved in a prescribed manner.

     We have adopted a rights agreement under which certain stockholders have the right to purchase shares of a new series of preferred stock at an exercise price of $140.00 per one one-hundredth of a share, if a person acquires more than 15% of our common stock. The rights plan could make it more difficult for a person to acquire a majority of our outstanding voting stock. The rights plan could also reduce the price that investors might be willing to pay for shares of our common stock and result in the market price being lower than it would be without the rights plan. In addition, the existence of the rights plan itself may deter a potential acquiror from acquiring us. As a result, either by operation of the rights plan or by its potential deterrent effect, mergers and acquisitions of us that our stockholders may consider in their best interests may not occur.

     If there are large sales of our common stock, the market price of our common stock could drop substantially.*

     If our existing stockholders sell a large number of shares of our common stock or the public market perceives that existing stockholders might sell shares of our common stock, the market price of our common stock could decline significantly. As of April 13, 2007, we had 24,797,684 outstanding shares of common stock. Of these shares, up to 15,147,259 shares of common stock are tradable under Rule 144 or Rule 701 under the Securities Act of 1933, as amended, or the Securities Act, subject in some cases to various vesting agreements, volume limitations and holding periods, and the remainder of the shares have been registered under the Securities Act and are freely tradable. In addition, 3,231,812 shares are held by our directors and executive officers and their affiliates and will be subject to volume, manner of sale and other limitations under Rule 144 under the Securities Act and various vesting agreements.

Item 2. Unregistered Sales of Equity Securities and Use of Proceeds

Unregistered Sales of Equity Securities

     On January 17, 2007, pursuant to the net exercise of a warrant, we issued 6,325 shares of our common stock to Alexandria Real Estate Equities Inc. at a purchase price of $6.00 per share. The sale and issuance of the common stock was exempt from registration pursuant to the Securities Act by virtue of Section 4(2) and/or Regulation D promulgated thereunder as a transaction not involving any public offering. We believe that the issuance is exempt from the registration requirements of the Securities Act on the basis that: (a) the purchaser of the securities represented that it was an accredited investor as defined under the Securities Act; (b) there was no general solicitation; and (c) the purchaser of the securities represented that it was purchasing such shares for its own account and not with a view towards distribution. Appropriate legends were affixed to the stock certificates issued in such transaction stating that the shares are not registered under the Securities Act and, therefore, cannot be resold unless they are registered under the Securities Act or unless an exemption to registration is available

Use of Proceeds from the Sale of Registered Securities

     Our initial public offering of common stock was effected through a Registration Statement on Form S-1, as amended (File No. 333-122156), which was declared effective by the SEC on June 2, 2005 and pursuant to which we sold 5,000,000 shares of our common stock. Morgan Stanley & Co. Incorporated acted as the sole book running and joint lead manager for the offering, Deutsche Bank Securities acted as co-lead manager for the offering, and co-managers for the offering were Pacific Growth Equities, LLC and Lazard Capital Markets. In July 2005, the underwriters partially exercised their over-allotment option and purchased an additional 9,569 shares of our common stock, and we received net cash proceeds of approximately $63,000, after deducting underwriting discounts and commissions and other offering expenses. As of March 31, 2007, all of the approximately $46.4 million in net proceeds received by us in the offering, after deducting approximately $6.2 million in underwriting discounts, commissions and other costs and expenses, had been used for general corporate purposes, including clinical trial, research and development, general and administrative and manufacturing expenses.

     No payments were made to directors, officers or persons owning ten percent or more of our common stock or to their associates, or to our affiliates, other than payments in the ordinary course of business to officers for salaries and to non-employee directors as compensation for board or board committee service.

Issuer Purchases of Equity Securities

     The following table provides information relating to repurchases of our common stock in the three months ended March 31, 2007:

Total Number of

Approximate

Shares

Dollar Value of

Purchased as

Shares that May

Total Number

Average

Part of Publicly

Yet Be Purchased

of Shares

Price Paid

Announced

Under the

Period

Purchased (1)

per Share

Program

Program

January 1, 2007 — January 31, 2007

—

$

—

N/A

N/A

February 1, 2007 — February 28, 2007

4,109

$

3.18

N/A

N/A

March 1, 2007 — March 31, 2007

3,403

$

5.15

N/A

N/A

Total

7,512

$

4.07

N/A

N/A

Item 3. Defaults Upon Senior Securities

None.

Item 4. Submission of Matters to a Vote of Security Holders

None.

Item 5. Other Information

     On April 25, 2007, XenoPort, Inc. announced positive top-line results from a Phase 3 clinical trial of the company’s most advanced product candidate, XP13512, for the treatment of symptoms of primary restless legs syndrome (RLS). XP13512 demonstrated statistically significant improvements compared to placebo on both of the co-primary endpoints of the trial and was well tolerated.

     This XenoPort study was a 12-week, double-blind, placebo-controlled Phase 3 clinical trial that enrolled 222 patients who were diagnosed with moderate-to-severe primary RLS. Patients were treated with either 1200 mg of XP13512 or placebo, given once per day. The co-primary endpoints for the clinical trial were the change from baseline for the International RLS (IRLS) rating scale score at end of treatment and the percentage of patients showing significant improvement on the Clinical Global Impression of Improvement (CGI-I) scale at end of treatment.

     Treatment with 1200 mg of XP13512 was associated with a statistically significant improvement in the co-primary endpoints compared to placebo. Improvements in the IRLS Scale were significantly greater for XP13512 than for placebo (-13.2 vs. -8.8: p=0.0002). At the end of treatment, significantly more patients treated with XP13512 were reported as “much improved” or “very much improved” on the CGI-I scale compared to those treated with placebo (76% vs. 39%: p < 0.0001).

     During treatment over the 12-week period, the most commonly reported adverse events for XP13512 versus placebo were somnolence (26.5% XP13512; 7.4% placebo) and dizziness (19.5% XP13512; 4.6% placebo). There were no reported serious adverse events in XP13512-treated patients.

Item 6. Exhibits

Exhibit
Number		Description of Document
3.1		Amended and Restated Certificate of Incorporation (1)
3.2		Amended and Restated Bylaws (1)
3.3		Certificate of Designation of Series A Junior Participating Preferred Stock (2)
4.1		Specimen Common Stock Certificate (3)
4.2		Fifth Amended and Restated Investors Rights Agreement, dated December 16, 2004, by and among the Company and certain stockholders of the Company (4)
4.3		Form of Rights Certificate (5)
10.4.1		Sublease Termination Agreement, dated January 22, 2007, by and between the Company and ILYPSA, Inc. (6)
10.24		XenoPort, Inc. Corporate Bonus Plan (7)
10.29†		Development and Commercialization Agreement, dated February 7, 2007, by and between the Company and Glaxo Group Limited
10.29.1		First Amendment to Development and Commercialization Agreement, dated May 4, 2007, by and between the Company and Glaxo Group Limited
31.1		Certification of the Chief Executive Officer pursuant to Securities Exchange Act Rules 13a-14(a) and 15d-14(a) as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002
31.2		Certification of the Chief Financial Officer pursuant to Securities Exchange Act Rules 13a-14(a) and 15d-14(a) as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002
32.1		Certification required by Rule 13a-14(b) or Rule 15d-14(b) and Section 1350 of Chapter 63 of Title 18 of the United States Code (18 U.S.C. §1350) (8)

SIGNATURES

     Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

		XenoPort, Inc.
		(Registrant)
		/s/ Ronald W. Barrett
May 9, 2007		Ronald W. Barrett
		Chief Executive Officer and Director
		/s/ William G. Harris
		William G. Harris
		Senior Vice President of Finance and
May 9, 2007		Chief Financial Officer (principal
		financial and accounting officer)
		/s/ Martyn J. Webster
		Martyn J. Webster
May 9, 2007		Vice President of Finance

EXHIBIT INDEX

Exhibit
Number		Description of Document
3.1		Amended and Restated Certificate of Incorporation (1)
3.2		Amended and Restated Bylaws (1)
3.3		Certificate of Designation of Series A Junior Participating Preferred Stock (2)
4.1		Specimen Common Stock Certificate (3)
4.2		Fifth Amended and Restated Investors Rights Agreement, dated December 16, 2004, by and among the Company and certain stockholders of the Company (4)
4.3		Form of Rights Certificate (5)
10.4.1		Sublease Termination Agreement, dated January 22, 2007, by and between the Company and ILYPSA, Inc. (6)
10.24		XenoPort, Inc. Corporate Bonus Plan (7)
10.29†		Development and Commercialization Agreement, dated February 7, 2007, by and between the Company and Glaxo Group Limited
10.29.1		First Amendment to Development and Commercialization Agreement, dated May 4, 2007, by and between the Company and Glaxo Group Limited
31.1		Certification of the Chief Executive Officer pursuant to Securities Exchange Act Rules 13a-14(a) and 15d-14(a) as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002
31.2		Certification of the Chief Financial Officer pursuant to Securities Exchange Act Rules 13a-14(a) and 15d-14(a) as adopted pursuant to Section 302 of the Sarbanes-Oxley Act of 2002
32.1		Certification required by Rule 13a-14(b) or Rule 15d-14(b) and Section 1350 of Chapter 63 of Title 18 of the United States Code (18 U.S.C. §1350) (8)