Biogen Idec’s multiple sclerosis drug Avonex might cause severe liver damage in rare cases, according to the company and the Food and Drug Administration.

The warning, which came on Wednesday, was another blow, though probably only a glancing one, to Biogen, already reeling from the halt in sales of its other multiple sclerosis drug, Tysabri, which was linked to a rare brain infection.

In a related development, GlaxoSmithKline said on Wednesday that the drug agency had ordered it to halt a trial of its multiple sclerosis drug, which is similar to Tysabri. A spokesman said the company understood the move to be a precautionary one that applied to trials of all drugs in the same class. In a letter posted on the agency’s Web site, Biogen said severe liver injury, including liver failure, had been reported “rarely” in patients taking Avonex. It said doctors should especially consider the risk when Avonex is used along with other drugs that can cause liver damage or in patients who drink alcohol.

Amy Ryan, a spokeswoman for Biogen, which is based in Cambridge, Massachusetts, said there had been only a handful of cases among the 130,000 patients using Avonex, which has been on the market since 1996. She said a “minor update” was being made to the drug’s label, upgrading liver damage from a “precaution” to a stronger “warning.”

It is not uncommon to find new side effects of drugs as they are more widely used. The label of Rebif, a drug similar to Avonex that is made by Serono, already comes with a warning about liver problems.

Still, with Tysabri off the market at least temporarily, Biogen will become more dependent for growth on Avonex, its biggest product, which had sales of $1.4 billion last year. On Wednesday, Biogen’s shares fell 88 cents, to $37.19

Both Ryan and an agency spokeswoman, Kathleen Quinn, said that there was no connection between the Avonex warning and that the Tysabri withdrawal and the timing were coincidental.

Biogen and Elan, its partner on Tysabri, suspended sales of that drug on Feb. 28 after two patients in clinical trials came down with a rare viral brain infection known as progressive multifocal leukoencephalopathy. The two patients, one of whom had died, had been taking both Tysabri and Avonex for more than two years in a clinical trial.

Source: International Herald Tribune