Tysabri Side Effects Linked to 9th PML Infection Case

A new case of a rare, often lethal, brain infection has been linked to the multiple sclerosis drug Tysabri, making it the ninth case of progressive multifocal leukoencephalopathy (PML) infection potentially caused by side effects of Tysabri since the drug was put back on the market in July 2006.

Biogen Idec Inc., the maker of Tysabri, reported the case on Friday, one week after the eighth case was reported. The company indicates that they will no longer report each individual cases of Tysabri PML infections, but will provide a weekly update on their website.

Progressive multifocal leukoencephalopathy, commonly referred to as PML, is a rare form of brain infection that causes damage and inflammation to the white matter areas of the brain. The infection often results in death after the degradation of certain brain functions. Affects of the infection can include impaired speech, weakness, loss of vision, paralysis and cognitive decline.

Tysabri (natalizumab) was approved in 2004 for the treatment of multiple sclerosis through regular intravenous injections. It was recalled from the market in 2005 after three patients developed the rare brain infection, two of whom died. The medication was reintroduced in July 2006 with stronger warnings about the potential Tysabri side effects, and the drug was only made available under strict usage guidelines to limit the risk of PML infections.

Since its return to the market, this most recent report is at least the ninth patient to develop the infection. Estimates indicate that about one in every 1,000 patients treated with the Tysabri experience the side effect. The lastest case involves a patient outside the United States who developed the brain infection after his 34th injection.

Tysabri is just one of several drugs that have been linked to the deadly PML brain infections in recent years. The psoriasis drug Raptiva was recalled in April due to PML infections, and the cancer drug Rituxan was recently connected to 57 cases of PML infection in a study published in the May 2009 issue of the medical journal Blood.