Biogen Idec and Elan have submitted studies to support their bid for approval. However, documents on the FDA website reveal that they did not show Tysabri to be clearly different from existing treatments for the bowel disorder.
Additionally, the drug was found to have lower effectiveness in treating Crohn’s than in treating MS. The FDA is now in the process of consulting an outside advisory panel on whether the drug should be approved.
Tysabri was pulled from the market just a few months after its launch in 2005, after three patients developed the brain infection progressive multifocal leukoencephalopathy, or PML. It was allowed back on the market in 2006 under certain restrictions, as the FDA decided its benefits for MS sufferers outweighed potential risks.
However, for Crohn’s disease patients, FDA reviewers have taken a different stance. “The benefit and risk considerations in the Crohn’s disease population are considerably different from those in the MS population,” they said in a report on the drug. “The treatment effect in the Crohn’s disease population was not as high as that in the MS population nor is it clearly distinguished from approved Crohn’s disease therapies.”