Biogen CEO: Tysabri patients will get PML

Expect the unexpected. That's essentially what Biogen Idec CEO James Mullen (photo) told investors yesterday when he predicted that more cases of a rare, fatal brain disorder will arise in Tysabri patients. "[W]e anticipate there will be some additional cases of PML," Mullen said, adding that he doesn't believe they would cause regulatory problems for the drug.

You'll recall that Biogen pulled Tysabri in 2005 when two patients acquired PML, or progressive multifocal leukoencephalopathy. It since has returned to the market under a patient-monitoring program. Despite the risks, many MS patients use Tysabri because it works. So many, in fact, that Mullen has been predicting blockbuster status for Tysabri by 2010. The drug's recent FDA approval for Crohn's disease could only help.

Recently, though, Biogen and marketing partner Elan warned doctors of the potential for liver damage in Tysabri patients. Injury could happen within six days of starting treatment, the letter warned.

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