Panel Supports Tysabri Return

The society estimates that around 400,000 Americans have the disease, while worldwide about 2.5 million people have MS. Twice as many women have it as men, and most of the diagnoses are made in people age 20 to 50.

The FDA's advisory panel recommended against Tysabri use in combination with other drugs that suppress the body's immune system, but it didn't rule out the possibility of its combination with other medications after further data on the risk of PML are collected and examined.

The panel believes PML is still possible in patients using Tysabri alone to treat MS and says more cases of the brain disease could surface and that more deaths could be reported. Still, other approved and widely used medications are known to have dangerous side effects, as well, the panel noted.

Biogen plans to follow up with patients on Tysabri if the drug gains the FDA's reapproval, saying everyone who takes it would be tracked to determine how many adverse incidents occur.

Additionally, Biogen said Tuesday it would query physicians after six months and track patient deaths through a national index and a collection of death certificates.

Elan and Biogen expect to follow 5,000 patients to monitor for side effects or serious infections. Biogen has said it would support Tysabri having a "black box warning," the FDA's strictest cautionary statement, outlining the risk of PML and saying that the drug shouldn't be used with other treatments for MS.

The FDA has granted Tysabri priority review, a status applied to drugs seen as significant advancements over existing therapies. Biogen and Elan say they will continue to work with the FDA on the details of a risk-management plan, and they expect a decision from the agency by March 29.