Biogen's only drug, the multiple sclerosis fighter Avonex, is under heavy fire from Serono's Rebif.

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Additionally, adverse events like diarrhea, hair thinning and back pain were more common in patients treated with Rebif.

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There's a new competing drug just out called Rebif from Swiss biotech outfit Serono, which has teamed up with pharmaceutical marketing powerhouse Pfizer.

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For the full year, sales of Rebif increased by 7.5 percent to 1.89 billion Euro, which offset slower sales growth for the Erbitux cancer drug.

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More upside could come over the next year, as trial data comparing Rebif to Copaxone, another MS drug made by Teva Pharmaceutical Industries, is due out.

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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.

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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.

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Merck (MRK) announced that profit more than doubled during the fourth fiscal quarter due to higher prices for its Rebif multiple sclerosis drug, as well as from cost savings from restructuring.

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Serono does have a huge U.S. business, thanks largely to Rebif, a multiple sclerosis treatment that has done well in the wake of the safety issues that faced Biogen Idec's Tysabri, which was recalled but is now being marketed in a limited fashion.

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