In the latest blow to the controversial multiple sclerosis drug Tysabri, the U.S. Food and Drug Administration has ordered a new label be put on the drug, warning that the risk of developing progressive multifocal leukoencephalopathy (PML), a rare but deadly brain infection, increases as more Tysabri infusions are received.
Natalizumab (Tysabri) first received FDA approval in November 2004, only to be pulled from the market three months later after several patients in clinical trials developed PML.
In June 2006, the FDA allowed the drug back on the market, but with strict conditions. According to those revised guidelines, Tysabri can only be administered by approved doctors at sites that register and comply with a patient-safety program. The new action was based on reports of 31 confirmed cases of PML as of Jan. 21, 2010.