Biogen CEO says expects more Tysabri PML cases

By Toni Clarke

BOSTON, March 18 (Reuters) - The chief executive of Biogen Idec Inc (BIIB.O) said on Tuesday he expects to see more cases of a potentially deadly brain infection in patients who take its multiple sclerosis drug Tysabri, but does not expect regulatory problems, provided the number remains small.

"We anticipate there will be some additional cases of PML," said CEO James Mullen, referring to progressive multifocal leukoencephalopathy, a brain infection that caused the drug to be temporarily suspended in 2005 after several patients developed the disease.

"There is no doubt that will create a lot of excitement in the short-term given the history of this product," he told investors at the Cowen & Co healthcare conference in Boston.

However, "I would see no regulatory problems."

Mullen said that in the event of a new case of PML, it would take investors and physician "a few weeks" to digest the news, he said.

Tysabri, which is made by Biogen and Elan Corp Plc (ELN.N) (ELN.I) of Ireland, was allowed back on the U.S. market in 2006 with restrictions.

"If we get a couple of cases of PML, the question will be what do you learn from them," Mullen said.

He reiterated his projection that 100,000 patients will be taking Tysabri by 2010, putting it on course to be a $1 billion-plus per year drug. (Reporting by Toni Clarke; Editing by Tim Dobbyn)