A warning about cases of rare brain infection has been included in updated safety information about the multiple sclerosis drug Tysabri, says the U.S. Food and Drug Administration.
The agency's update says the risk of developing progressive multifocal leukoencephalopathy (PML) "appears to increase with the number of Tysabri infusions received." The average number of infusions received by patients before they were diagnosed with PML was 25, Dow Jones reported.
"There is minimal experience in patients who have received more than 35 infusions of Tysabri," according to the FDA update. Patients receive the drug through an intravenous infusion about once a month.
The FDA emphasized that the overall rate of PML among patients taking Tysabri remains below the one-in-1,000 rate noted on the label, Dow Jones reported.
Concerns about PML prompted the FDA to pull Tysabri from the market for 18 months in 2005. Since the drug was allowed back on the market, there have been 13 confirmed cases of PML.