Study raises questions about virus in Tysabri users

A new study of the multiple sclerosis drug Tysabri shows some patients developed the virus associated with a potentially deadly brain infection, although not the infection itself, according to an analyst’s report.

Citing a summary of a presentation to be presented in April at the American Academy of Neurology, Corey Davis, an analyst at Natixis Bleichroeder, said an examination of 175 patients treated at one center found two cases of JC virus — one in the cerebrospinal fluid and one in the plasma.

But he noted that none of the cases showed any signs of progression to progressive multifocal leukoencephalopathy, or PML, the potentially deadly brain infection.

‘‘We do not know the reliability, sensitivity, nor specificity of the assay being used by this one group to detect the presence of the virus, and hence are hesitant to draw too many conclusions,’’ Davis said.

Tysabri, made by Biogen Idec Inc., of Cambridge and Elan Corp. PLC, of Ireland, was temporarily suspended from the market in 2005 after several patients developed the disease, but allowed back in 2006 with certain restrictions after US regulators decided MS patients were willing to accept the risks in return for the potential benefits.

A spokeswoman for Biogen was not immediately available for comment.
(Reuters)