Biogen reports 10th case of PML brain infection

A 10th patient taking Tysabri, known generically as natalizumab, has developed a potentially deadly brain infection since the multiple sclerosis drug was reintroduced to the market in July 2006.

Biogen Idec Inc, the Cambridge, Massachusetts-based biotech company released the news on its website late Friday.

Tysabri, which Biogen sells in conjunction with Irish drugmaker Elan Corp, is considered critical to the future growth of both companies.

The drug was temporarily withdrawn from the market in 2005 after it was linked with a brain infection known as progressive multifocal leukoencephalopathy, or PML. It was brought back in 2006 with stricter safety warnings.

Natalizumab, a monoclonal antibody, affects the immune system and increase risk of viral infections of the brain have been reported with natalizumab.

Sales of the drug have failed to live up to expectations. Biogen has recently begun taking a more aggressively upbeat tone in marketing the drug, insisting physicians are becoming more comfortable with risk of PML. Even so, some analysts believe doctors may take patients off the drug for certain periods of time.

“We view increased adoption of “drug holidays” as a strong possibility,” said analyst Eun Yang of Jefferies & Co.

BOSTON (Reuters)