European regulators have concluded that US group Biogen Idec and Irish drugmaker Elan’s multiple sclerosis therapy Tysabri should come with a warning about a potentially higher risk of liver damage in patients taking the drug.

The move follows a review by the European Medicines Agency’s Committee for Medicinal Products for Human Use of 29 reports of liver injury in patients treated with Tysabri (natalizumab), 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.

The decision comes hot on the heels of a similar move by US regulators in February, which saw Biogen warn of the potential risks of higher levels of hepatic enzymes and bilirubin - a key marker of severe livery injury that could lead to the need for a liver transplant or even patient death - in letter to healthcare professionals, shortly after a similar warning was added to the drug’s label for its Crohn’s disease indication.

Doctors on both sides of the Atlantic have been advised to closely monitor the liver function of patients taking Tysabri, and it was stressed that therapy should be discontinued in those deemed at risk.

Safety profile
This is not the first time Tysabri’s safety profile has been under review. The drug first hit the market in 2004 and many analysts had expected it 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 by US and European regulators, Tysabri was allowed to return to pharmacy shelves in July 2006 for the treatment of MS, with certain restrictions, as regulators felt that as long as patient were aware of the risks they could benefit from its use.