* 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 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The drug was temporarily withdrawn from the market in 2005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
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
(Reporting by Toni Clarke; Editing by Steve Orlofsky and Lisa