The multiple sclerosis drug Tysabri has been linked to two new cases of progressive multifocal leukoencephalopathy (PML) in Europe. PML is a rare and often-fatal brain infection, where there is inflammation of the brain’s white matter. In 2005, shortly after its FDA approval, Tysabri was withdrawn from the market following three PML deaths linked to the drug. Tysabri returned to the market in 2006, with labels outlining the risk of PML. The FDA allowed the drug back on the market after determining that Tysabri’s potential benefits should be available to MS patients who are willing to accept the risk. Tysabri is co-marketed by Elan Corp. and Biogen Idec Inc. According to a Biogen spokesperson, the company expected to see additional PML cases. As of the end of June, more than 31,800 patients were using Tysabri. The drug was also recently approved for treatment of Crohn’s disease in adults.
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