NEW YORK (Reuters) - Biogen Idec and its partner Elan Corp said on Tuesday no new cases of a potentially deadly brain infection have been seen among patients taking their Tysabri multiple sclerosis drug since it was re-introduced in July 2006.

The companies said no cases of progressive multifocal leukoencephalopathy, or PML, were seen by the end of March among about 26,000 patients taking the drug.

Given the favorable safety findings, the companies said they were moving towards their goal of having 100,000 patients on the medicine by the end of 2010.

Tysabri, which has been shown highly effective in treating the progressive neurological disease, was temporarily suspended from the market in 2005 after several patients developed PML. But it was allowed back in 2006 -- with certain restrictions -- after U.S. regulators decided MS patients were willing to accept the risks in return for the potential benefits.

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The new safety data were presented on Tuesday at the annual meeting of the American Academy of Neurology in Chicago.

(Reporting by Ransdell Pierson; Editing by Braden Reddall)