Shares in Biogen and Elan plunge on two new cases of PML in Tysabri patients
Shares in Irish biotechnology firm Elan plunged 37.9% to $12.45 after new cases of a rare brain disease in patients taking its key product Tysabri (natalizumab) were reported.
Two patients on the multiple sclerosis drug have developed progressive multifocal leukoencephalopathy, the condition that prompted the product's 2005 market withdrawal.
Shares tumbled after the new PML cases were disclosed in a filing with the US Securuties and Exchange Commission on July 31. On that day, development partner Biogen Idec's stock price fell 17.6% to $57.49 in after-hours trading.
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