US warns of risk rise with more Tysabri infusions

The risk of a potentially fatal brain disorder with Biogen Idec Inc’s multiple sclerosis drug Tysabri increases as patients receive more infusions, U.S. health officials warned on Friday.

The prescribing instructions for Tysabri will be updated to warn of the higher risk with more treatment, the Food and Drug Administration said. Elan Corp co-markets the drug.

The FDA said the warning was based on 31 confirmed cases of progressive multifocal leukoencephalopathy (PML), a brain infection that can be fatal. Eight patients have died.

“Based on the available information, the FDA believes that the clinical benefits of Tysabri continue to outweigh the potential risks,” the FDA said in a notice on its website.

Tysabri was temporarily withdrawn from the market in 2005 because of its link to PML.

Biogen spokeswoman Naomi Aoki said “there was nothing I thought was new” in the FDA notice.

“Either it was included as part of our last label update or it was information that we are making available on a monthly basis,” she said.

Biogen updates the number of PML cases each month to doctors on request but no longer posts the figure on its website or issues a press release.

Elan officials were not immediately available for comment.

Tysabri is given as a single infusion every four weeks. About 66,000 people worldwide have been treated with the drug since it reappeared on the market in 2006, the FDA said.

The PML rate for patients given at least one infusion is 0.5 cases per 1,000 patients, the FDA said. For patients given at least 24 infusions, the PML rate is 1.3 per 1,000.

The FDA move comes two weeks after a similar announcement by European regulators, who also said Tysabri’s benefits outweighed risks.

The drug carries a boxed warning, the strongest type for prescription drugs, about the PML risk. All patients must enroll in a monitoring program for PML or other serious infections. The drug’s generic name is natalizumab.

The FDA had said in September the PML rate appeared to increase with the number of infusions but said at the time it was not requiring any changes to the drug’s warnings.

The FDA posted the notice at http://www.fda.gov/Drugs/DrugSafety/PostmarketDrugSafetyInformationforPatientsandProviders/ucm199872.htm.

By Lisa Richwine

WASHINGTON (Reuters)