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    New Details on Suspension of MS Drug Tysabri

    3 Patients in Clinical Trials Developed Rare Disease; 2 Died

    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.

    Doctors' Advice for Patients

    Tysabri is given by injection every four weeks. That would mean that patients who took the drug only while it was on the market got a maximum of one to three doses, Koralnik tells WebMD.

    "We would think they are not at any risk of developing PML now if they haven't manifested any overt neurological disease different from their baseline," he says.

    Patients should talk to the doctors and have their blood screened, says Annette Langer-Gould, MD, of Stanford University medical school's neurology department. Langer-Gould, who also serves in Stanford's department of health research and policy, contributed to a journal report on one of the confirmed PML cases.

    'Very Rare' Disease

    PML is "very rare," even in people with weakened immune systems, says Langer-Gould.

    People with MS are not believed to be at higher risk for PML, and the disease is not thought to be contagious, says the FDA's web site.

    The patient who survived the confirmed case of PML temporarily had a worsening of his symptoms about three months after stopping Tysabri. What may have happened, says Koralnik, is that the patient's white blood cells were able to get back into the brain at that point to fight the virus.

    "It's clear that Tysabri and other medications of this class are extremely promising to treat a variety of crippling conditions for which there is no cure," says Koralnik. "But we have to learn, move forward, and understand better ... the exact mechanisms to the reactivation of this virus, how to prevent it in the future, and how to monitor for such reactivation."

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