European regulators review risk, benefit of Biogen Idec, Elan’s Tysabri

European regulators announced that the Committee for Medicinal Products for Human Use started a review of the benefits and risks of Biogen Idec and Elan’s multiple sclerosis drug Tysabri (natalizumab), following reports of 23 cases of progressive multifocal leukoencephalopathy (PML) since the agent has been on the market. Shares in Biogen Idec fell as much as 6 percent, while Elan saw a drop of 21 percent in its shares.

Commenting on the news, JP Morgan analyst Geoffrey Meacham said that "if the 23 PML cases is accurate…then that would imply an additional 10 cases since early September." In July, Biogen Idec said the number of reported cases was 11.

The European Medicines Agency’s committee noted that the investigation will look at whether “any additional measures” are required to ensure the safe use of the drug. Christopher Raymond, an analyst from Robert Baird, remarked that European regulators are unlikely to remove Tysabri from the market, but may recommend that patients receiving the drug on a long-term basis take a break to reduce the risk.

With regards to the PML cases, analysts expressed caution, with Leerink Swann’s Joshua Schimmer saying that the “rates are exactly as we predicted in July," adding that double-counting some patients may have pushed the actual number up too high. Sanford C. Bernstein analyst Geoff Porges said the significance of the number of cases was hard to gauge without further details, but added that these “are likely to alarm physicians whose comfort with the product had been increasing in recent months.”

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