Tysabri natalizumab: Postmarketing study data

Biogen Idec said 1 patient receiving Tysabri who initially tested negative for anti-JCV antibodies tested positive 15 months later, which the company said indicates exposure to the JC virus at some point between the 2 tests. The patient developed progressive multifocal leukoencephalopathy (PML) 2 months after testing positive for the virus. As of Jan. 20, the company said that there have been 201 confirmed cases of PML worldwide in patients receiving Tysabri, of which 42 have been fatal. ...