Drugmakers Biogen Idec Inc. and Elan Corp. Plc. have warned doctors of significant liver injury suffered by some patients taking the multiple sclerosis drug Tysabri, U.S. regulators said on Wednesday.
Signs of liver damage occurred in some patients as early as six days after their first dose of Tysabri, the drug companies said in a letter to doctors from posted on the Food and Drug Administration Web site. The companies co-market the drug, with Biogen taking the lead in the U.S.
The letter dated February 2008 reflects a label update approved by the FDA in January as part of an expanded clearance for the drug to treat the bowel disorder Crohn's disease, an FDA spokeswoman said.
Biogen estimates that less than one in 1,000 patients taking the drug for either MS or Crohn's disease suffered from serious liver injury according to post-marketing reports, Biogen spokeswoman Shannon Altimari said.
About 21,000 patients were taking the drug as of the end of December, Altimari said. Tysabri had $129 million in fourth-quarter sales, and Biogen has forecast it to become a $2 billion-a-year blockbuster.
In some cases, liver problems occurred after the drug was stopped and then restarted, confirming the Tysabri link, the letter said.
Severe liver injury may lead to death or the need for a transplant.
Stocks fall on news
Biogen shares fell over 2 percent on Nasdaq, while shares of Elan sunk 5.7 percent on the New York Stock Exchange.
Wall Street analysts said investors were selling on old news because the liver risk has been debated since at least last year, including at an FDA advisory panel.
"The stocks are clearly overreacting because whenever you have a new FDA safety warning or a Dear Doctor letter, it puts the fear of God into stocks," Natixis Bleichroeder analyst Corey Davis said.
Biogen also markets Avonex, one of the world's best-selling MS treatments with sales of $500 million in the fourth-quarter. Tysabri is considered a far-more potent treatment, however.
The FDA advisory panel reviewing the drug for Crohn's discussed the potential liver risks last year.
Longstanding safety concerns
Tysabri has been haunted by safety concerns since it was approved.
Sales of the drug were suspended in 2005 amid three cases of a brain infection, known as known as progressive multifocal leukoencephalopathy, or PML. The drug returned to the market in 2006 with limits after the FDA decided that MS patients were willing to accept the risks in light of possible benefits.
Biogen shares were off $1.36 at $60.17 in afternoon trading on the Nasdaq. Shares of Ireland's Elan traded in New York were off $1.38 at $22.93.
