From Cinderella story, to heartache, to back on the market, back to side-effect disaster, it's been one wild ride for multiple sclerosis drug Tysabri and the stocks of its owners, Biogen Idec
The drug increases the risk of developing progressive multifocal leukoencephalopathy, or PML, a serious brain infection. The infection is caused by the usually relatively harmless JC virus, which the immune system usually takes care of. Tysabri weakens the immune system -- multiple sclerosis is essentially the immune system attacking body's nervous system -- but in the process of trying to control the immune system, Tysabri can potentially allow infections to occur.
Just "potentially" because not everyone has the JC virus floating around their bloodstream, waiting for their host to take an immune-system weakening drug before launching its attack. And no virus means no PML.
The inclusion of the JC virus status as a risk factor for Tysabri patients developing PML is good news for Quest Diagnostics
Tysabri is arguably the best drug available to treat multiple sclerosis, but many of the JC-virus-negative patients haven't taken the drug for fear of the chance of developing PML, however small it may be. With the ability to determine the risk, patients who don't have the virus are more likely to switch from Teva Pharmaceuticals'
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