Multiple Sclerosis Drug Tysabri Associated with Risk of Brain Infection, FDA Warns

The U.S. Food and Drug Administration (FDA) announced a new warning for the multiple sclerosis (MS) drug Tysabri on February 5, 2010.

An advisory sent by the FDA to patients and medical professionals warned that treatment with Tysabri can increase the risk of developing progressive multifocal leukoencephalopathy (PML), a rare disorder that affects myelin, the substance that protects nerves in the white matter of the brain. The advisory notes that the risk of developing PML increases with the administration of additional injections of the medication.

“This is not new information,” said Dr. John Richert, executive vice president for research and clinical programs at the National Multiple Sclerosis Society. “We've had this information for a couple of months now.”

Tysabri received attention in September 2009 when it was linked to three new cases of PML, the first reported cases of the condition since June 2009. Tysabri was approved for the treatment of MS in November 2004  and was pulled from the market three months later, following reports of patients developing PML. The medication became available again in July 2006.

“The risk-benefit ratio continues to be about the same as we anticipated since the time the drug was brought back on the market,” said Dr. Richert.

“Right now, Tysabri is the most efficacious drug that's ever been approved for the treatment of relapsing-remitting MS, which represents 85 percent of all patients out there who have MS,” said the director of neurology at the Scott & White University Medical Campus, Dr. Jeffrey Tramonte, adding, “It also carries the single most dangerous risk factor, and that's PML.”

As of January 21, 2010, 31 cases of PML have been attributed to Tysabri treatment, though the FDA does not suggest pulling Tysabri from the market. The FDA states that the clinical benefits of the medication continue to outweigh the potential risks.

“I think as long as the medication is being prescribed for the appropriate patient with MS, then the new information we have today is not going to alter medication management,” said Dr. Tramonte.

Additional information about drugs and drug side effects may be found on Drugwatch.com.