Four new cases of a life-threatening brain illness have been linked to Tysabri, the multiple sclerosis drug made by Biogen Idec. According to a Biogen spokeswoman, there are now 35 patients who have developed progressive multifocal leukoencephalopathy (PML) since Tysabri was allowed back on the market. As of February 9, eight of the patients have died. In 2005 Biogen, which is based in Massachusetts, and its partner Elan, which is based in Dublin, pulled Tysabri from the market after three patients developed PML. Two of those patients died. There was a link between PML and Tysabri. However, the FDA later decided that Tysabri’s benefits of slowing multiple sclerosis relapses outweighed its risks, and in 2006 it allowed Biogen and Elan to resume selling Tysabri. No PML infections were reported for approximately 2 years after Tysabri came back to market. Tysabri’s label carries a warning about the risk of PML. According to the Biogen spokeswoman, the likelihood of developing PML increases with the amount of time a patient uses Tysabri.
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