European drug regulators have recommended against the use of Tysabri as a treatment for Crohn's disease.
The European Medicines Agency said the risk of serious infection outweighs the relatively modest benefit conferred by the multiple sclerosis drug, made by Biogen Idec and Elan, on Crohn's patients.
Biogen and Elan, which is based in Ireland, said they will appeal the decision and expect a ruling on the appeal by the first quarter of 2008.
Tysabri was taken off the market in 2005 after being linked with three cases of a potentially deadly brain infection known as progressive multifocal leukoencephalopathy, or PML. It was reintroduced a year ago and is available in the United States through a safety-monitoring program known as Touch.
Crohn's disease is a chronic inflammatory disease of the gastrointestinal tract that affects about one million people worldwide.
The product will be reviewed by US experts for use in Crohn's at an advisory meeting on July 31st.