The FDA continues to receive reports of progressive multifocal leukoencephalopathy (PML) in patients receiving Tysabri. Tysabri was approved by the FDA for the treatment of relapsing forms of multiple sclerosis (MS) in November 2004 and for moderately to severely active Crohn’s disease in January 2008. From July 2006, (when Tysabri marketing resumed) to September 8, 2009, 13 reported cases of Tysabri-related PML were confirmed worldwide in patients being treated for MS with Tysabri monotherapy. Of these, four cases were patients in the United States (U.S.). There have been no postmarketing reports of PML in patients treated with Tysabri for Crohn’s disease. Less than 2% of Tysabri use in the U.S. has been in patients with Crohn's disease.
The risk for developing PML appears to increase with the number of Tysabri infusions received. The number of monthly infusions of Tysabri in the 13 patients who developed PML ranged from 12 to 35 infusions. The average number of infusions received before the diagnosis of PML was 25. There is minimal experience in patients who have received more than 35 infusions of Tysabri.
The overall rate of developing PML with Tysabri therapy in patients who have received at least one infusion remains below one per 1,000 patients. Based on available data from the U.S. and outside of the U.S., the current rate of PML in patients who have received at least 24 infusions ranges from 0.4 to 1.3 per 1,000 patients.
At this time, the FDA is not requiring changes regarding PML to the Tysabri prescribing information or to the Tysabri risk management plan, called the TOUCH Prescribing Program. All patients receiving Tysabri therapy in the U.S. must be enrolled in the TOUCH Prescribing Program. Under this program, every patient who receives Tysabri is closely monitored for the occurrence of PML and other serious opportunistic infections.

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