Biogen Idec’s share price took another knocking yesterday after the firm, together with the US regulatory agency, said that its multiple sclerosis offering, Avonex (interferon beta-1a), could cause severe liver damage, including liver failure.

In a letter sent to healthcare professionals, Biogen Idec, which hit the headlines earlier this month after it suspended its new, highly-touted MS drug, Tysabri (natalizumab) [[01/03/05a]], said it was updating the Avonex prescribing information to include the new warning.

Although the firm noted that some of the cases of liver damage had occurred “in the presence of other drugs that have been associated with hepatic injury,” it has amended the label to say: “The potential for [liver] injury should be considered when Avonex is used in combination with other products associated with [liver] injury, or when new agents are added to the regimen of patients already on Avonex.”

Avonex won US approval back in 1996, and was also designated an orphan drug, entitling it to seven years’ marketing exclusivity. This was not due to expire until 2003, but Switzerland’s Serono was able to launch its MS drug, Rebif (interferon beta-1a), onto the US market after demonstrating superiority to Avonex in head-to-head clinical trials [[08/03/02a]], [[08/10/01d]], [[08/05/01b]].