Biogen, Elan push back on Tysabri study

Biogen Idec and Elan are soft-pedaling research released yesterday that showed the virus responsible for a potentially fatal brain disorder is activated--and the patient's immune system weakened--by their multiple sclerosis drug Tysabri.

As you know, a Harvard Medical School doctor and his colleagues studied 19 patients who had just started Tysabri treatment. Urine samples showed that levels of the virus leapt after one year on the drug. But Biogen maintains that a patient's virus levels by themselves don't indicate whether he or she will end up getting progressive multifocal leukoencephalopathy, and that's why the company is studying a host of other potential contributing factors.

Getting to the bottom of just what causes PML in Tysabri patients could help Biogen and partner Elan further grow sales of the drug. Tysabri was pulled from the market after PML cropped up in a few patients, and then reintroduced under a risk-management program. Since then, a handful of Tysabri patients have developed the disorder. (Some 56,000 patients are using Tysabri now, Elan says.) Doctors have learned how to better treat PML, however, and some are experimenting with treatment holidays to help prevent the infection.

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