Both medicines are similar to Avonex, and, like Avonex, they cause flu-like side effects.
Both of the patients were also taking Avonex, a second drug made by Biogen Idec.
Biogen's only drug, the multiple sclerosis fighter Avonex, is under heavy fire from Serono's Rebif.
Also, Biogen faces heavy competition with two of its big drugs: Avonex (multiple sclerosis) and Amevive (psoriasis).
Avonex and similar drugs decrease the rate of MS relapses by 30%, Gilenya by 50%, Tysabri by 70%.
But since then, the price premium has decreased after Biogen Idec raised the price on Avonex 9% last December.
Avonex and Tysabri treat the neurological disease multiple sclerosis, and make the company the leading producer of MS treatments.
While Avonex sales haven't been hurt much yet, investors fear they will be.
The reason: Biogen's (nasdaq: BIIB - news - people ) top-selling drug was another multiple sclerosis drug, Avonex.
Tysabri, however, is so good that it may steal sales from Avonex.
If patients switch off BG-12, they might be more likely to try Gilenya than go back to Avonex, meaning a lost sale to Biogen.
Porges points out that because of the side effect issues, doctors may choose to try Copaxone instead of Avonex as half of a drug combo.
Before it was pulled, Tysabri cost more than Avonex or Copaxone, a treatment marketed by Teva Pharmaceutical Industries (nasdaq: TEVA - news - people ).
Unlike Avonex, Tysabri and almost every other MS drug approved until recently, all of which often require painful injections (and often cause fatigue and depression), BG-12 is a pill.
Then Serono (nyse: SRA - news - people ), a Swiss biotech, did a study showing that its drug Rebif might work better than Avonex for some patients.
More recently, Serono (nyse: SRA - news - people ), a Swiss biotech, was able to get its drug, Rebif, onto the U.S. market despite Avonex's orphan status.
While Astrue was at Biogen (nasdaq: BGEN - news - people ), he helped Avonex, a treatment for MS, get past an existing drug to reach the market.
In his early presentations, Kellogg said the medicine Biogen licensed from Elan (nyse: ELN - news - people ) might be used mainly for those that had failed Avonex.
Years later, it is the first pill that can slow the progress of MS. All competing drugs, such as Avonex and Tysabri from Biogen Idec and Copaxone from Teva Pharmaceutical Industries, have to be injected.
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By owning full rights to the drug, Biogen will be able to more easily streamline its marketing with other MS drugs, including Avonex and Tecfidera, formerly known as BG-12, a pill that is awaiting FDA approval.
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She and Rauch both point out that Elan is a lot more likely to benefit from Antegren sales than Biogen-Idec (nasdaq: BIIB - news - people ), which may have to cannibalize sales of its existing MS treatment Avonex to sell Antegren.
Biogen Idec shares were whacked in late February when the company and partner Elan pulled their multiple sclerosis drug Tysabri from the market after the two companies confirmed that a patient who had been taking Tysabri with Avonex, another drug, for two years had died.
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