Last Updated: January 15, 2008 (Reuters Health)

WASHINGTON (Reuters) - Biogen Idec and Elan Corp won U.S. approval on Monday to market their drug Tysabri (natalizumab ) for treating Crohn's disease.

The drug is already sold for treating multiple sclerosis with tight restrictions and a strong warning about a potential for progressive multifocal leukoencephalopathy. The companies must put similar limits on sales for Crohn's disease, the Food and Drug Administration said.

The FDA approved Tysabri for adults with moderate to severe Crohn's disease who have evidence of inflammation and have a poor response to, or cannot take, other therapies.

In one Elan-sponsored study, 60% of Tysabri patients responded to treatment after 12 weeks of therapy, compared with 44% who got a placebo.

Another study tested patients who initially responded to Tysabri, following them for an additional year. Fifty-four percent of Tysabri patients had a sustained response through 12 months, compared with 20% of placebo patients, Elan said.

Tysabri is an "important step" in treating Crohn's but "one that carries serious risks," said Dr. Joyce Korvick, deputy director of the FDA division that reviews gastroenterology drugs. "Health-care providers must carefully monitor patients for these risks," Dr. Korvick told reporters by telephone.

Sales of the drug were suspended in 2005 in response to three cases of progressive multifocal leukoencephalopathy, or PML. The drug returned to the market in 2006 with limits after the FDA decided MS patients were willing to accept the risks in light of possible benefits.

Dr. Korvick said the FDA ordered similar restrictions for Crohn's sales as it did for MS. Among them, patients must acknowledge risks and agree to be monitored for problems.

FDA reviewers in the past have estimated the risk of developing PML is 1 in 1,000 over 18 months of Tysabri use, but caution the calculation could change after more experience with the drug. There is no known treatment for PML, which is usually fatal within six months.

The companies expect Tysabri will be available to Crohn's patients by the end of February, Elan said in a statement.

European regulators have recommended against use of Tysabri for Crohn's disease. Biogen and Elan have said they expect a final decision from the European Commission during the first quarter of 2008.

Date Posted: January 18, 2008