FDA approves new drug for treating MS

Washington -- The Food and Drug Administration has licensed a new medication to treat the flare-ups of multiple sclerosis that occur in the majority of the 400,000 patients diagnosed with this chronic disease of the brain and spinal cord.

The drug, natalizumab, which will be marketed as Tysabri, was granted accelerated approval based on promising first-year results from a two-year trial now concluded. Its data are being analyzed.

But until the final results are in, physicians who specialize in treating patients with multiple sclerosis are eyeing the new offering with cautious optimism.

"I'm excited about what I consider to be this preliminary data," said Jack Burks, MD, a Reno, Nev., neurologist who specializes in treating patients with multiple sclerosis. "But I am waiting until the first quarter of next year when I can get the two-year data to see if my excitement is sustained or not. We've had the experience with drugs that have better one-year data than two-year data."

However, his patients are already clamoring for Tysabri, which many think may represent a cure.

"I would not take anyone who is doing well off their medication. If it ain't broke we don't need to fix it," said Dr. Burks, who is also the vice president and chief medical officer of the Multiple Sclerosis Assn. of America.

"The clinical trial results indicate that the drug is very effective in relapsing forms of MS and appears to be well-tolerated," said Aaron Miller, MD, chief medical officer of the National Multiple Sclerosis Society. The relapsing-remitting form of MS is the most common form of the disease and is characterized by symptoms that become dramatically worse before subsiding totally or partially.

Dr. Miller also recommends close monitoring of the drug for any potential safety problems as it becomes more widely used.

How it works

The new drug, which is administered by intravenous infusions every four weeks, is the sixth drug now approved for the long-term treatment of MS and the first humanized monoclonal antibody available to treat the disease.

"We believe Tysabri will revolutionize the treatment of MS and become the leading choice for patients and physicians," said James C. Mullen, chief executive officer of Biogen Idec Inc., which manufactures the drug with Elan Corp.

"Tysabri is a significant breakthrough for patients with MS," said Kelly Martin, president and chief executive officer of Elan.

Tysabri is designed to interfere with movement of potentially damaging immune cells from the bloodstream across the blood-brain barrier and into the brain and spinal cord. Although the cause of MS remains unknown, it is widely considered to be an autoimmune disease.

Tysabri apparently blocks the immune cells' movement by attaching to alpha 4-integrin, a protein on the surface of immune T cells that normally enables the cells to pass through the blood-brain barrier.

The one-year data for Tysabri showed a 66% reduction in relapses compared with patients on placebo in one trial and a 54% relative reduction in relapses for those taking Tysabri in combination with a second drug approved to treat MS -- Avonex, or interferon beta-1a -- as compared with those taking Avonex alone.

Common side effects include headache, fatigue, urinary tract infection, depression, lower respiratory tract infection, joint pain and abdominal discomfort.