New Details on Suspension of MS Drug Tysabri

June 9, 2005 -- New information has surfaced about the rare but often lethal disease that prompted the removal of Tysabri, a new multiple sclerosis (MS) drug. At least three cases have been identified.

Tysabri was approved by the FDA last November. In late February, Tysabri's maker, Biogen Idec, voluntarily pulled it from the market. Tysabri's maker, Biogen Idec, voluntarily pulled it from the market. The suspension followed reports of one confirmed and one suspected case of progressive multifocal leukoencephalopathy (PML), a rare but often lethal viral disease of the central nervous system.

Now, three cases of PML have been confirmed; two of those were fatal. All three confirmed cases occurred in people who had taken Tysabri for more than two years in clinical trials. Two patients were also taking another MS drug called Avonex, according to reports in The New England Journal of Medicine's July 28 edition.

Possible 4th Case

There have also been media reports of a possible fourth case of PML. However, that "is still being reviewed and has not been confirmed," says FDA spokeswoman Lenore Gelb.

Gelb tells WebMD that Biogen Idec, a WebMD sponsor, notified the FDA of an adverse event experienced by a fourth patient who had been taking Tysabri and Avonex. FDA documents show that the patient was a 48-year-old woman, but it's not yet known if she had PML.

Biogen Idec spokeswoman Amy Brockelman says a newspaper headline last week incorrectly reported that the fourth patient was dead. The patient is not dead, and Biogen's safety evaluation of the drug is "ongoing," Brockelman tells WebMD.

What's Known So Far

All three confirmed cases occurred in people who had been taking Tysabri for more than two years as part of clinical trials of the drug, says Igor Koralnik, MD, associate professor of neurology at Harvard Medical School.

That's much longer than the handful of months in which Tysabri was on the market, says Koralnik, who co-wrote a journal editorial about Tysabri and also directs the HIV/Neurology Center at Boston's Beth Israel Deaconess Hospital.

It's not known if the combination of drugs in two of the confirmed cases might have been important or if the association was with Tysabri alone, says Koralnik.

Two of the three confirmed cases were MS patients. The third was a 60-year-old man with Crohn's disease. His death was originally attributed to another condition.

About 3,000 people took part in the clinical trials, which included patients with MS, Crohn's disease, and rheumatoid arthritis, says a Biogen Idec letter.