Shares in Biogen Idec and Elan both took a hit yesterday on news that the companies have written to healthcare professionals in the USA warning that patients taking Tysabri may be at a higher risk from liver injury.

The move was spurred by post-marketing reports of “clinically significant” liver injury in patients taking the drug, with signs of substantially elevated hepatic enzymes and bilirubin (a breakdown product of haemoglobin) observed as early as six days after the first dose was administered.

As the company notes, higher levels of hepatic enzymes and bilirubin are a key marker of severe livery injury that could lead to the need for a liver transplant or even patient death, and it stressed that Tysabri (natalizumab) should be discontinued in patients deemed at risk.

A warning over the risk of liver damage was added to the prescribing information for the drug in its Crohn's disease indication when it was approved in the US in January, and the label for its original multiple sclerosis use has now also been updated.

Checkered history
Tysabri first hit the market in 2004 and many analysts had expected the drug to generate peak annual sales of as much as $4 billion, but it was promptly taken off the market in March 2005 after three patients developed a potentially fatal brain infection called progressive multifocal leukoencephalopathy. However, following an extensive safety review on both sides of the Atlantic, Tysabri was allowed to return to pharmacy shelves in July 2006 for the treatment of MS, with certain restrictions.

Shares in Biogen Idec closed down 2.3% at $60.13, while those in Elan dropped 6.3% to $22.77 after a day of heavy trading, reflecting investor concern over this latest hit to the drug’s safety profile.