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FDA Lets MS Drug Tysabri Return

Strict Rules Focus on Rare, Potentially Deadly Brain Infection
WebMD Health News
Reviewed by Louise Chang, MD

June 5, 2006 -- The FDA is letting the multiple sclerosis (MS)multiple sclerosis (MS) drug Tysabri back on the market under a restricted distribution program.

The FDA first approved Tysabri in November 2004. Tysabri’s maker, Biogen-Idec, took Tysabri off the market in February 2005 after three people out of about 3,000 patients taking Tysabri in clinical trials developed a rare, serious brain infection called progressive multifocal leukoencephalopathy (PML). Two of those patients died.

The FDA is rolling out a risk-minimization plan along with Tysabri's return to the market. The plan is designed to inform patients, doctors, pharmacists, and infusion centers about Tysabri’s risks and to quickly flag PML cases in patients taking Tysabri.

However, FDA officials aren’t ruling out the possibility of more cases of PML in patients taking the drug.

Rare Return to Market

“This is one of the very rare cases in which a drug withdrawn from the market for safety reasons has been returned back to the market after appropriate steps have been taken,” the FDA’s Steven Galson, MD, MPH, told reporters in a conference call.

Galson directs the FDA’s Center for Drug Evaluation and Research. He says the FDA has worked “closely” with Biogen-Idec on the new plan.

In Tysabri’s clinical trials, about one in 1,000 participants developed PML after taking Tysabri for up to two years. It’s not clear if that rate will hold in the general public or for longer use, the FDA’s Russell Katz, MD, told reporters in the teleconference. Katz works in the neurology products division of the FDA’s Center for Drug Evaluation and Research.

PML is still a risk with Tysabri, note both Galson and Katz.

"Without prohibiting use of the drug, you can never be sure that this won’t happen again. But we think that the steps that we’ve taken are prudent to reduce that risk,” Galson says.

More Cases Possible

“There’s much we don’t know about this,” Katz says. “We expect, yes, that there will be other cases and there probably will be additional deaths. This is balanced against the significant benefit that we believe the drug confers,” Katz says.

Speaking about PML, Katz says, “We don’t know how to predict who’s going to get it, we don’t know how to prevent it, and we don’t know how to treat it if it occurs.”

Galson notes that until Tysabri’s new risk-minimization program has been in effect for some time and physicians have seen patients go through rounds of therapy, “there may be additional things that we will learn.”

“The size of the clinical trials that have taken place and the duration is not adequate for us to know for certain that there isn’t something else that’s going to happen or further information that will be gained about this condition,” Galson says.

“We made the assessment that the benefits of this drug outweigh the risk for this particular condition,” Galson says. “Multiple sclerosis … is a debilitating condition and we are certain that patients are willing to take this risk because of the potential benefits of the drug. So that’s why we’re doing it.”

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