Tysabri, a medication that treats the symptoms of the autoimmune disease multiple sclerosis, may offer new hope for patients, but it also carries small life-threatening risks, according to three new studies published in this week's New England Journal of Medicine.
Multiple sclerosis, or MS, affects approximately 400,000 Americans, mostly young adults. While the cause is unknown, MS can lead to serious nervous system damage. The debilitating symptoms, such as numbness and muscle weakness, often get worse over time, and current medications are not always completely effective in treating it.
That's why researchers and patients were so interested in Tysabri, which came on the market several years ago and was sold by Biogen Idec and Elan Pharmaceuticals. Clinical trials showed that it could alleviate symptoms.
However, last February two patients developed a rare viral infection while taking the drug, and one of these patients died. As a result, the manufacturers removed Tysabri from the market so the risks could be investigated.
The new studies released today shed new light on how the drug helps MS patients, and how often it may cause serious side effects. The studies are likely to become a major topic of discussion next week when a U.S. Food and Drug Administration committee meets to discuss using Tysabri to treat patients with relapsing forms of multiple sclerosis.
The first study looked at more than 940 MS patients, about 600 of whom took Tysabri and the others a placebo. The patients on Tysabri showed improvement in their symptoms, and none developed progressive multifocal leukoencephalopathy, or PML, the disease that killed the MS patients when Tysabri was on the market. PML is a rare but often fatal viral disease of the nervous system.
However, in an additional study, PML did strike two patients. This study followed 1,171 MS patients who showed symptoms despite treatment with interferon, another MS medication. In this study, half of the patients took Tysabri and interferon, while the other half received a placebo and interferon. This trial also showed that Tysabri improved symptoms.
PML is linked to a virus that causes destruction of the protective covering of nerve fibers in the brain. Many people are exposed to the virus in childhood, but it tends to come out of dormancy only among those with weakened immune systems, according to the FDA. There is no cure, and people with PML usually die one to four months after its onset.
Knowing this risk, the researchers of the third published study attempted to find other potential cases of PML among the approximately 3,000 patients who received Tysabri in clinical trials. But no other cases were found, meaning that roughly one person out of every 1,000 who took this drug in clinical trials developed the disease.
Because of the new data, the FDA will make recommendations next Tuesday and Wednesday on whether Tysabri should be returned to the market and become available for use outside of clinical trials.
A doctor with the National Multiple Sclerosis Society said his organization did not have an opinion on whether the FDA should approve Tysabri but instead provided information to help the agency make a decision.
"Our feeling has been that our role is to do everything we can to make sure that the FDA gets all the information it needs to make the wisest decision possible," said Dr. John Richert, the society's vice president for research and clinical programs.