New Data for Achillion's Elvucitabine Demonstrate Drug's Safety, Efficacy and Suitability for Combination Therapy in HIV-Infected Patients

NEW HAVEN, Conn., Jan. 31, 2008 (PRIME NEWSWIRE) -- Achillion Pharmaceuticals, Inc. (Nasdaq:ACHN), a leader in the discovery and development of small molecule drugs to combat the most challenging infectious diseases, today announced positive safety and efficacy results from two ongoing Phase 2 clinical trials studying elvucitabine in patients infected with Human Immunodeficiency Virus (HIV). Elvucitabine, Achillion's HIV product candidate, is an L-cytosine nucleoside analog reverse transcriptase inhibitor (NRTI) that has previously demonstrated potent antiviral activity against HIV, including strains resistant to other NRTIs.

The objectives of these trials include demonstration of the safety, tolerability and antiviral activity with a 10 mg dose of elvucitabine, as compared to 3TC (lamivudine), in a standard triple-combination regimen in two distinct patient populations: treatment-naive patients and treatment-experienced patients, particularly those harboring the M184V mutation in the reverse transcriptase protein of HIV.

24-Week Safety and Efficacy Findings

In the first trial, results at 24 weeks in treatment-naive patients demonstrated that elvucitabine had a potent anti-viral effect similar to 3TC, with a mean change in HIV-RNA from base-line in the elvucitabine treatment group of -3.0 log10 (+/- 0.6) vs. -3.2 log10 (+/- 0.5) in the 3TC treatment group. In the elvucitabine-treated group, 96% of patients reached undetectable viral load, defined as achieving fewer than 50 copies/ml after 24 weeks of therapy, compared to 94% in 3TC group. Elvucitabine was well-tolerated and demonstrated a safety profile comparable to 3TC for both incidence and severity adverse events. Additional results from this trial at both 48 and 96 weeks will be announced as available, and full 24-week data will be presented at a future scientific forum.

Short-term Resistance Findings

The second trial, designed to provide insight into elvucitabine's ability to address difficult-to-treat patients harboring the M184V mutation, included a first phase consisting of exploratory viral kinetic and pharmacokinetic analysis, followed by an open label extension phase. After 14 days of therapy, the Company noted similar viral load reductions in the elvucitabine and 3TC treatment groups. Importantly, however, the trial results demonstrate significant improvement in response in the second open-label extension phase where 8 of 14 patients who received elvucitabine, or 57%, had achieved 0.5 log10 reduction or more in viral load, likely related to the fact that elvucitabine reaches steady-state levels in patients after approximately 21 days of treatment. These data will be presented at a future scientific forum.

"These data show that elvucitabine can achieve substantial antiviral effect in both naive and treatment-experienced patients with the M184V mutation, with a safe and tolerable profile. Viral load decline in the treatment experienced patients appears to be correlated with achieving steady state elvucitabine concentrations, which occur at approximately 21 days, due to the long half-life of elvucitabine," said Elizabeth A. Olek, D.O., Vice President and Chief Medical Officer. "Results from these trials also confirm the safety and efficacy of elvucitabine in a 10 mg daily dose. Elvucitabine's combination of long half-life and favorable resistance profile position it as a potentially important alternative to currently available nucleosides in the treatment of HIV patients."

"We are extremely pleased that a once-daily 10 mg dose of elvucitabine is safe and efficacious in treatment naive as well as treatment experienced patients in these studies. The results are positive indicators to prospective partners with whom a fixed dose combination of elvucitabine and other antiretroviral agents can be developed. With these data, we plan to advance collaboration discussions currently underway. With its long half-life as a potential safeguard against the emergence of resistance, we believe that elvucitabine will be an important entry in the armamentarium for HIV patients and their physicians," commented Michael D. Kishbauch, President and CEO of Achillion.

Study Designs

The first Phase 2 clinical trial (ACH443-015) is a randomized, double-blind study in patients infected with wild-type HIV-1 virus. The trial included a 12-week blinded treatment period after which responders (patients with viral loads below 400 copies/mL, or less than 2 log10 decrease) continued to a now ongoing 84-week open-label extension period. The trial enrolled 78 subjects who were randomized 1:1 into two treatment groups: 10 mg/day elvucitabine with 600 mg/day efavirenz and 300 mg/day tenofovir or 300 mg/day 3TC with 600 mg/day efavirenz and 300 mg/day tenofovir.

The second Phase 2a clinical trial (ACH443-014A) is a randomized, double-blind, comparative viral kinetic and pharmacokinetic study in patients infected with HIV-1 virus containing the M184V variant. The trial included a 14-day blinded treatment period after which trial participants were given elvucitabine plus optimized background medications during a now ongoing 48-week open-label extension period. The trial enrolled 18 subjects who were randomized 1:1 into two treatment groups: 10 mg/day elvucitabine with background antiretroviral therapy or 300 mg/day 3TC with background antiretroviral therapy.

Teleconference

Achillion will hold its regularly scheduled year-end earnings announcement and conference call and simultaneous webcast on Wednesday, February 27, 2008 at 4:30 p.m. Eastern time. During that call, members of management will review the results of the elvucitabine clinical trials outlined above, as well as other program updates. To participate in the conference call, please dial (877) 440-5788 in the U.S. or (719) 325-4928 for international callers. A live audio webcast of the call will be accessible at www.achillion.com, under the News Center section of the website. Please connect to Achillion's website several minutes prior to the start of the broadcast to ensure adequate time for any software download that may be necessary.

A replay of the webcast will be available on www.achillion.com. Alternatively, a replay of the conference call will be available starting at 7:30 p.m. Eastern time on February 27, 2008, through 11:59 p.m. Eastern time on March 1, 2008 by dialing (888) 203-1112 or (719) 457-0820. The replay passcode is 4744390.

About Elvucitabine

Elvucitabine, Achillion's HIV product candidate, is an L-cytosine nucleoside analog reverse transcriptase inhibitor (NRTI) that has demonstrated potent antiviral activity against HIV, including strains resistant to other NRTIs. NRTIs are the predominant class of drugs for use in HIV combination therapy and are frequently prescribed given their established potency, favorable short and long-term safety profile and fewer and less severe adverse side effects. Clinical and pre-clinical data collected to date indicate that elvucitabine can be dosed as a 10 mg pill once daily and may be used in combination therapy. In addition, the L-nucleoside configuration of the compound may provide protection against mitochondrial toxicity, a serious side effect often seen with D-nucleosides. Finally, elvucitabine has been demonstrated to have a longer half-life than other approved NRTIs, providing a potential barrier to the emergence of drug resistance in patients who are less than perfectly compliant.

About Achillion

Achillion is an innovative pharmaceutical company dedicated to bringing important new treatments to patients with infectious disease. The company's proven discovery and development teams have advanced multiple product candidates with novel mechanisms of action. Achillion is focused on solutions for the most challenging problems in infectious disease -- HIV, hepatitis and resistant bacterial infections. For more information on Achillion Pharmaceuticals, please visit the company's web site at www.achillion.com or call Achillion at 1-203-624-7000.

This press release includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 that are subject to risks, uncertainties and other factors, including statements with respect to Achillion's expectations regarding the timing and duration of clinical trials, the Company's expectations regarding the release of data from ongoing clinical trials and its beliefs regarding the effect of the results of collaboration discussions. Among the factors that could cause actual results to differ materially from those indicated by such forward-looking statements are: unexpected regulatory actions or delays; uncertainties relating to results of clinical trials, including additional data relating to ongoing clinical trials and Achillion's ability to obtain additional funding required to conduct its research, development and commercialization activities along with Achillion's ability to attract and develop potential collaboration relationships. These and other risks are described in the reports filed by Achillion with the U.S. Securities and Exchange Commission, including its Quarterly Report on Form 10-Q for the nine-months ended September 30, 2007. All forward-looking statements reflect Achillion's expectations only as of the date of this release and should not be relied upon as reflecting Achillion's views, expectations or beliefs at any date subsequent to the date of this release. Achillion anticipates that subsequent events and developments may cause these views, expectations and beliefs to change. However, while Achillion may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so.

ACHN-G

CONTACT: Achillion Pharmaceuticals, Inc.
         Investors:
         Mary Kay Fenton
         (203) 624-7000

         MacDougall Biomedical Communications, Inc.
         Media:
         Christopher Erdman
         (781) 235-0306
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