Serono Soars, Biogen Falls on FDA's Rebif Decision

Shares of Serono(SRA Quote) were soaring in the premarket session while Biogen's(BGEN Quote) were falling after the Food and Drug Administration cleared the way for Serono to sell a multiple sclerosis drug in the U.S.

Serono said it expects to start selling its Rebif treatment in certain U.S. markets within days after the FDA overturned the orphan drug status of Biogen's Avonex. The orphan status grants several years of market exclusivity for companies that develop expensive medicines to treat relatively rare diseases.

Serono forecasts that its Rebif sales could approach $1 billion by 2005, although Biogen released a statement saying it's confident Avonex will continue to be the leading drug in the U.S. market.

On Instinet, Serono was gaining 14.6% to $22.45, while Biogen was falling 13.1% to $49.