The US label for Biogen Idec's and Elan’s Tysabri (natalizumab) was updated to indicate that the risk of progressive multifocal leukoencephalopathy (PML) in patients taking the drug increases with longer usage. The labelling revision notes that for patients taking the multiple sclerosis treatment for 24 to 36 months, the risk of PML is "generally similar" to the 1 in 1000 rate seen in clinical trials, but there is limited data for the drug beyond three years.
Biogen Idec had previously reported that it was in discussions with the FDA regarding an update to Tysabri’s label to include a duration-related risk. Commenting on the labelling update, Joel Sendek, an analyst at Lazard Capital Markets, noted that he did “not expect physicians to significantly change their Tysabri prescribing habits in the near-term," and said he continues to believe the product will have sales of $1.1 billion in 2010. However, Jim Birchenough from Barclays Capital suggested that the revised label will ultimately slow sales growth of the drug.
In October, European regulators initiated a review of the benefits and risks of Tysabri following reports of 23 cases of PML since the agent has been on the market.
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