FDA Drug Safety Communication

FDA continues to evaluate the risk of progressive multifocal leukoencephalopathy (PML), a rare but serious brain infection associated with use of Tysabri (natlizumab) for the treatment of multiple sclerosis (MS) and Crohn's disease. The FDA has updated the Tysabri label to give new information about the size of this risk, as well as to include new safety information about patients who have taken other drugs that suppress the immune system, who may be at a higher risk for PML.

The revised drug label includes:

A table summarizing rates of PML with Tysabri use according to the number of infusions (how long the drug is taken or duration of exposure).

Information on a newly identified PML risk factor. Patients who took an immune system suppressing medication (e.g., mitoxantrone, azathioprine, methotrexate, cyclophosphamide, mycophenolate) prior to taking Tysabri have been shown to be at an increased risk for developing PML. The Tysabri label already warned that using immune system-suppressing medications at the same time as Tysabri may increase the risk of developing PML.

The FDA anticipates that the new PML information in the label will aid healthcare professionals in assessing the risk for PML and in discussing that risk with their patients. The Tysabri label will be updated periodically as new information about the risk for PML becomes available.

Based on the available information to date, the FDA continues to believe that the benefits of taking Tysabri outweigh the potential risks. Tysabri will continue to be available to patients only through a restricted distribution program called the Tysabri Outreach Unified Commitment to Health (the TOUCH Prescribing Program).

The FDA issued a previous Drug Safety Communication (DSC) on the risk of PML with the use of Tysabri on February 5, 20102.

View the full FDA Drug Safety Communication on FDA.gov