New health risks are associated with multiple sclerosis drug Tysabri (natalizumab), said the U.S. Food and Drug Administration (FDA) in a recent announcement about its new warning on the medication’s label, HealthDay reported.

The FDA sent the warning to doctors and patients about increased risks for a fatal brain infection called progressive multifocal leukoencephalopathy (PML) that can result when the drug is continuously used.

The new label warning was based on 31 newly reported PML cases as of January 21 of this year. Many of the new cases were among European patients who took other drugs that also increased their risks for PML development.

“This is not new information. We’ve had this information for a couple of months now, [but] the labeling in the past did not make a distinction between the time frames that people were on the drugs,” said John Richert, MD, executive vice president for research and clinical programs at the National Multiple Sclerosis Society. “The risk-benefit ratio continues to be about the same as we anticipated since the time the drug was brought back on the market.”

Though Tysabri carries the dangerous risk of developing PML, experts agree that it’s the most efficient drug for MS treatment.

“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 Jeffrey Tramonte, MD, director of neurology at the Scott & White University Medical Campus in Round Rock, Texas. “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.”

The FDA seems to agree. The agency has not suggested discontinuing Tysabri, stating that its clinical benefits outweigh its potential risks.

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