DUBLIN, Nov 7 (Reuters) - Ireland's Elan and U.S. drugmaker Biogen Idec have amended the label of their multiple sclerosis drug Tysabri to reflect the increased risk of contracting a potentially deadly brain infection, Elan said in a statement on Saturday.
Last month European regulators began a review of the drug following reports of 23 cases of progressive multifocal leukoencephalopathy, or PML.
The label changes specified that the occurrence of PML in patients treated for 24 to 36 months is generally similar to the 1-in-1,000 rate seen in clinical trials, Elan said.
Tysabri was temporarily withdrawn from the market in 2005 after being linked with PML. It was reintroduced in July 2006 with stricter safety warnings.
Tysabri is considered the most important driver of growth for Elan and Biogen and shares in both companies fell sharply after the most recent PML cases were reported last month.

(Reporting by Padraic Halpin; editing by Chris Pizzey) Keywords: ELAN/ (padraic.halpin@reuters.com; Reuters Messaging: padraic.halpin.reuters.com@reuters.net; +353 1 500 1504)

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