Tysabri

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Parkes, analyst at ING in London, said it was difficult to gauge potential impact. "If the story is true and the case is confirmed, it highlights two things -- the possibility that we could still see further cases, and the risks in trying to get the product back on to the market," he said. "It would not be good news. The share price was reflecting optimism that the product gets back to the market but I think it's early days -- it's pure speculation until the safety review is complete and we've seen the data." Blair analyst Winton Gibbons said even if Biogen Idec and Elan were able to devise a reasonable hypothesis to explain the drug's connection with PML, he believes it is "unlikely Tysabri will return in the short term." Gibbons said there is a "modest probability" the drug could return to the market after a clinical trial testing the hypothesis on the cause of PML, a process that would take about three years. Last week, Elan Chief Executive reiterated his confidence that Tysabri would return to the market. At the company's annual meeting in Dublin he said the safety probe into Tysabri was on track to conclude by mid-to-late summer, after which discussions with the FDA could begin. Elan stock has fallen 70 percent since the suspension of Tysabri, and it had been pinning hopes of a return to profitability on the drug. It clawed its way back from a brush with bankruptcy three years ago. The market also had high hopes for the product, which underwent fast-track approval by the FDA. (Additional reporting by Jodie Ginsberg in Dublin and Steenhuysen in Chicago)

© Reuters 2005. .