Biogen Idec's (NASDAQ:BIIB) multiple sclerosis drug Avonex accounted for $2.2 billion or about 70% of the big biotech company’s product revenue through the first nine months of this year. So it stands to reason that the company wants to preserve those sales as best it can in the face of new competition. On Thursday Biogen said a study showed that an experimental drug -- essentially a long-acting version of its Avonex injectable treatment -- met goals for showing effectiveness in patients at both two-week and four-week dosings. Avonex is a once-weekly treatment. Biogen is testing the new drug known ...