Tysabri Linked to Serious Brain Infection PML in 79 People, 16 Deaths

According to new data released by Biogen Idec, their once-recalled multiple sclerosis drug Tysabri has been linked to at least 79 confirmed cases of progressive multifocal leukoencephalopathy (PML), including at least 16 deaths caused by the serious brain infection.

Tysabri (natalizumab) is an intravenous injection given every 28 days to treat multiple sclerosis (MS) and Crohn’s disease. Manufactured by Biogen Idec Inc. and marketed with Elan Corp PLC, Tysabri has been shown to prevent relapse, cognitive decline and vision loss associated with MS. Sales of Tysabri bring in about $1 billion annually.

A Tysabri recall was issued in 2005 after three users developed PML, a rare and life-threatening brain infection, which attacks the central nervous system, damaging and inflaming the white matter areas of the brain. The drug was reintroduced in July 2006 with stronger warnings about the potential risk of a PML brain infection from Tysabri and the drug was only made available under strict usage guidelines.

Biogen says the rate of infection stands at about 1 per every 1,000 patients, and that the climbing number of confirmed brain infections since Tysabri was reintroduced to the market, could be due to the number of patients who have been on the drug for longer than two years. It appears that the risk of infection increases with the duration patients are on the drug.

Patients who have received 12 Tysabri infusions or less have a rate of PML infection of 0.01 per 1,000. However, patients who have been on the drug longer and have received more than 24 Tysabri injections have a risk of 2.05 per 1,000. The FDA first alerted patients and doctors that the risk increased with each injection in a Tysabri PML warning issued in February.

PML is believed to be caused by the common JC virus, and Tysabri may reduce the ability of the immune system to combat the virus.

In 2009, reports of PML brain infections from Raptiva, a psoriasis drug marketed by Genentech, Inc., led to that drug being removed from the market. Unlike Tysabri, which has remained available with strong warnings for consumers, it was determined that the risk of Raptiva brain infection side effects outweighed the benefits provided in treating psoriasis.