BOSTON, Oct. 23 (Reuters) - European regulators said they have begun a review of the multiple sclerosis drug Tysabri in light of 23 reports of a potentially deadly brain infection known as progressive multifocal leukoencephalopathy, or PML, since the drug has been on the market.
Tysabri is made by the U.S. biotechnology company Biogen Idec Inc (BIIB.O) and Elan Corp Plc ELN.I ELN.N of Ireland. It was temporarily withdrawn from the market in 2005 after being linked with PML. It was reintroduced with stricter safety warnings in July 2006.
The European Medicines Agency said it has initiated the review to discuss any additional measures necessary to ensure the safe use of Tysabri.
Biogen's shares fell 6 percent to $44.45 in early trading while shares of Elan fell nearly 17 percent to $5.36. (Reporting by Toni Clarke, editing by Gerald E. McCormick)