* Biogen reports 10th case of Tysabri brain infection
* Shares fall 6.8 percent
* Tysabri seen as key growth driver for Biogen (Adds share price, additional analyst comment)
BOSTON, June 29 (Reuters) - A 10th patient taking Biogen Idec Inc’s (BIIB.O) Tysabri has developed a potentially deadly brain infection since the multiple sclerosis drug was reintroduced to the market in July 2006, sending the company’s shares down nearly 7 percent.
The Cambridge, Massachusetts-based biotech company released the news on its website late on Friday.
Tysabri, which Biogen sells in conjunction with Irish drugmaker Elan Corp PlcELN.I, 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The drug was temporarily withdrawn from the market in 2005 after it was linked with a brain infection known as progressive multifocal leukoencephalopathy, or PML.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.
Sales of the drug have failed to live up to expectations. It generated $227 million in the first quarter, less than the $246 million analysts had expected.
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, whose 2009 sales estimate of $1 billion for Tysabri remains unchanged.
Analysts at Deutsche Bank downgraded Biogen shares to “hold” from “buy,” and said the company no longer warranted being one of the bank’s ‘top picks’ in 2009.
Biogen shares were down 6.8 percent at $46.66 in morning Nasdaq trading. (Reporting by Toni Clarke; Editing by Steve Orlofsky and Lisa Von Ahn)