Sept. 16 (Bloomberg) -- Biogen Idec Inc. and Elan Plc’s Tysabri has been linked to 13 cases of a deadly brain disease since the drug was reintroduced in July 2006, regulators said.

New safety information for the treatment for relapsed multiple sclerosis and Crohn’s disease was posted today on the U.S. Food and Drug Administration’s Web site. Eleven cases of progressive multifocal leukoencephalopathy, or PML, had been reported as of July 24, according to data compiled by Bloomberg.

The FDA temporarily suspended sales of Tysabri in 2005 after three cases of PML were reported. Patients successfully pleaded for the product’s return and since then, investors and doctors have closely monitored reported side effects. Less than 1 patient in 1,000 develops PML, with those who get more monthly infusions having increased risks, according to the FDA.

“PML remains a rare adverse event in Tysabri-treated patients,” said Jennifer Neiman, a spokeswoman for Cambridge, Massachusetts-based Biogen, in an e-mail today. “To date, the incidence is consistent with what is outlined in the product labeling and within what was expected when Tysabri was reintroduced more than three years ago.”

Four of the cases reported since 2006 were in U.S. patients, the FDA said.

Kelly Martin, chief executive officer of Dublin-based Elan, said Sept. 14 that he wasn’t aware of any new, unannounced cases of the brain disorder.

To contact the reporter on this story: Catherine Larkin in Washington at clarkin4@bloomberg.net.

Last Updated: September 16, 2009 16:56 EDT