But safety concerns, including an increased risk for fatal infections, cancer and heart and liver problems have weighed somewhat on the commercial viability of FTY720 and cladribine.

Biogen Idec tried to seize on these worries Wednesday by highlighting the clean safety record observed so far with BG-12.

"All the advantages of a multiple sclerosis pill go away if there are serious safety issues," said Al Sandrock, Biogen's research head in charge of neurology.

Oral multiple sclerosis drugs will get a thorough vetting by researchers and Wall Street next month at the American Academy of Neurology annual meeting, where full phase III data from Novartis' and Merck's drugs will be presented for the first time.

Later in Wednesday's investor meeting, Biogen presented new market research showing that 74% of neurologists expected to increase use of Tysabri over the next six months while only a small percentage of doctors, 3%, said they planned to prescribe less Tysabri.

Biogen pointed to this market research as evidence that Tysabri sales could rebound after falling back late last year due to additional reports of Tysabri patients being diagnosed with progressive multifocal leukoencephalopathy, or PML, a serious brain infection.

Tysabri sales rose 137% to $813 million in 2008, but in the fourth quarter Tysabri sales totaled $218 million, down 8% sequentially from the third quarter and well below Street estimates.

Wednesday, Biogen executives laid out plans to re-accelerate Tysabri patient growth, including new research into treatments that could potentially reverse the effects of PML.

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