EU watchdog places Biogen’s Tysabri under scanner

European regulators yesterday said they were examining 23 cases of patients who developed potentially fatal brain infections after taking multiple sclerosis drug Tysabri manufactured by Biogen Idec Inc, a global leader in innovative therapies, and Elan Corp, an Irish drug maker that markets Tysabri in Europe.

The European Medicines Agency's Committee for Medicinal Products for Human Use, known as CHMP, reported there have been a higher number of progressive multifocal leukoencephalopathy, or PML, cases linked to Tysabri (natalizumab).

The agency, which regulates drugs in Europe, said it will review the risks and benefits of Tysabri and discuss whether added measures are needed to assure safety.

The move sent the stock of Biogen Idec, based in Cambridge, down $3.42, or 7.2 per cent, to $43.81 on the Nasdaq exchange. Shares of Elan plunged $1.13, or 17.5 per cent, to $5.31 on the New York Stock Exchange.

Biogen Idec spokeswoman Jennifer Neiman said the incidents of the brain infection, progressive multifocal leukoencephalopathy, remain extremely rare - well within the range of one in 1,000 cases noted on the drug's label.

''Tysabri is a very compelling option for the treatment of multiple sclerosis,'' Neiman said, ''and overall, the benefit-risk profile for the product continues to be very favorable.''