The use of this drug can lead, in some instances, to the development of a rare and incurable nervous system disease known as progressive multifocal leukoencephalopathy, or PML, that is usually fatal after six months.
For this reason, Tysabri was pulled off the U.S. market in February 2005 after two patients developed the condition but was later allowed back under a restricted distribution system.
According to latest reports on the FDA's web site Friday, the agency said the treatment effect of Tysabri in Crohn's Disease is "considerably different from those in the MS population" and said the drug wasn't "clearly distinguished" from other approved Crohn's treatments.
Biogen, which manufactured the drug in collaboration with Elan, is seeking FDA's approval for Tysabri to treat Crohn's disease of patients who have failed other therapies. The disease causes inflammation of the intestines and affects about 1 million people worldwide.
The FDA said combining Tysabri with other treatments could increase risk of PML. Patients with Crohn's Disease are more likely to be on steroids or chronic immunosuppressant therapy than MS patients.
The federal agency also added that the drug appeared to be effective in preventing inflammation of the intestine wall in Crohn's Disease patients. If approved for the new use, Tysabri would compete with Remicade, the leading Crohn's treatment made by Johnson and Johnson.
