'Cloud of risk' swells around Tysabri

The multiple sclerosis drug Tysabri has hit an obstacle on its comeback trail. Drug makers Biogen Idec and Elan warned doctors yesterday that serious liver injury could arise in patients using the med. In some patients, signs of liver problems showed up just six days after their first dose.

The new warning was included in prescribing information for Tysabri use in patients with Crohn's disease, a new indication approved by the FDA last month. Now it's being added to inserts for patients using the product for MS. The rate of liver injuries is less than one in 1,000 patients.

You'll recall that Tysabri was taken off the market in 2005 after a few patients developed a rare neurological disorder. In 2006, the FDA allowed it to be sold under a restricted distribution program. Since then it's been slowly gaining market share; it brought in $343 million for Biogen last year.

After nabbing the new indication last month, Biogen said it hoped to attract 100,000 new patients to the drug by 2010. We'll see whether the new warnings have any effect on those numbers. Some analysts are wary; one called Tysabri "a drug with a cloud of risk hanging over it."

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