Biogen wants to put PML marker on Tysabri label

Biogen Idec ($BIIB) has followed through on its promise to keep the public apprised about the safety of its multiple sclerosis drug Tysabri. Monthly, the company has been updating us with new case counts of the potentially fatal brain infection PML, or progressive multifocal leukoencephalopathy. Now, it and partner Elan want to update the drug's label to include not only warnings of the risk of PML, but also a biomarker that may predict that risk for each individual patient.

The infection prompted withdrawal of the drug back in 2005, and Tysabri came back onto the market in 2006 under a risk-management program. But new PML cases cropped up, which spawned a European safety review and inspired new revisions of the drug's FDA label. Nonetheless, the drug officially became a blockbuster, topping $1 billion in sales last year.

If FDA allows this latest label revision, the drug could get a boost. The biomarker in question is an antibody to the JC virus, which causes PML. Biogen is developing an antibody-detection test, but it's still in clinical trials. If approved, the diagnostic would help patients and doctors feel more comfortable with the drug, even as a first-line treatment, analyst say. That, in turn, could have quite an effect on sales. A "game-changer," as one MS expert said. Stay tuned.

- see the Bloomberg story

Editor's Note: This article was updated to clarify the label-change request made by Biogen and Elan. The change would note that the JC virus antibody could be a predictor of PML risk. It would not recommend a new diagnostic test.