Biogen Idec and Elan’s fast-growing multiple sclerosis drug, natalizumab (Tysabri), has been connected to 13 cases of a potentially fatal brain infection, according to an FDA notice reported on today by Bloomberg News.
Cases of progressive multifocal encephalopathy, or PML for short, have been adding up since the drug was re-introduced to the U.S. market in July 2006 after it was withdrawn because of the risk. Despite the chance of infection, which the FDA pegged at about 1 in 1,000, patients have continued to seek out the treatment, which physicians say is the most effective therapy on the market for multiple sclerosis. More than 40,000 people worldwide were taking the drug at the end of March, according to Cambridge, MA-based Biogen (NASDAQ: [[ticker:BIIB]]).
Behind the scenes, researchers have intensified efforts to find out what it is about natalizumab that might be making people vulnerable to this particularly dangerous brain infection, and how to treat it. One Harvard Medical School neurologist, Igor Koralnik, presented research last week at at a European medical meeting that suggested patients’ immune system T cells didn’t work as well against the virus linked to PML when they were on the MS treatment, according to a separate Bloomberg report. Biogen said the results weren’t definitive.
