Shares in Elan have fallen almost 8 per cent in Dublin this morning after it issued a warning of significant liver injury suffered by some patients taking its drug Tysabri.
At 9.45am Elan shares were down 132 cents at €15.27, a fall of 7.9 per cent.
According to a statement from US regulators, signs of liver damage occurred in some patients as early as six days after their first dose of Tysabri, Elan and Biogen said.
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.
The companies co-market the multiple sclerosis drug, with Biogen taking the lead in the United States.
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, a Biogen spokeswoman said.
About 21,000 patients were taking the drug as of the end of December, she added. Tysabri had $129 million in fourth-quarter sales, and Biogen has forecast it to become a $2 billion-a-year blockbuster.
Biogen shares fell over 2 per cent on Nasdaq, while shares of Elan sunk 5.7 per cent on the New York Stock Exchange.