DOCTOR'S VIEW ARCHIVE
Medical Author: Melissa Stoppler, M.D.
Medical Editor: Barbara K. Hecht, Ph.D.
FDA Public Health Advisory Suspended Marketing of Tysabri (natalizumab)
March 3, 2005, FDA is issuing this public health advisory to inform patients and health care providers about the suspended marketing of Tysabri (natalizumab) due to two serious adverse events reported with its use. FDA has received a report from Biogen Idec, the manufacturer of Tysabri, of one confirmed, fatal case and one additional case of progressive multifocal leukoencephalopathy (PML) in patients receiving Tysabri for multiple sclerosis (MS). Both patients were enrolled in a long-term clinical trial and had been taking Tysabri for more than two years. There have been no previous cases of PML reported in patients taking Tysabri. For the rest of the FDA press release, please click here.
Multiple sclerosis is a chronic disease of the nervous system most commonly occurring in adults between the ages of 20 and 50, and is caused by inflammation and destruction of the myelin sheath, a protective covering that surrounds nerve tissue. When myelin is damaged, the underlying nerves eventually become damaged, leading to disrupted transmission of signals within the nervous system. While the exact cause of multiple sclerosis is unknown, doctors believe that exposure to a toxin or infectious agent early in life might trigger an abnormal response by the body's own immune system that leads to the progressive damage.
Typically, a patient experiences the sudden onset of mild to severe, short- to long-term symptoms that is sometimes referred to as an exacerbation or attack of MS. The symptoms of multiple sclerosis are extremely variable and related to the function of the affected nerve fibers. During attacks, those with multiple sclerosis may experience disturbances in vision, speech, walking, writing, and memory. Muscle spasms, fatigue, numbness, and prickling pain are also common symptoms along with a loss of sensation, dizziness, and occasionally hearing loss. Attacks may be brief or continue for months to years. In the most common form of multiple sclerosis, attacks are followed by a complete or partial disappearance of the symptoms (remission) until another attack occurs (relapse).
A new drug called Tysabri (natalizumab), given as an intravenous injection once per month in a doctor's office, led to a two-thirds reduction in the relapse rate of multiple sclerosis in a study conducted at Rush University Medical Center. Tysabri is a bioengineered antibody produced in the laboratory that interferes with certain functions of the immune response. In November 2004, the U.S. Food and Drug Administration (FDA) approved Tysabri as a treatment for all relapsing forms of MS. This drug received accelerated approval due to its substantial benefit for patients with MS, and clinical trials are still ongoing to evaluate the long-term effectiveness of the drug.
Adverse reactions to Tysabri include hypersensitivity reactions to the drug (including rare anaphylactic reactions) in less than one per cent of those taking the medication. A slightly increased incidence of infections was also seen in those using Tysabri. Tysabri use is contraindicated in anyone who has a history of hypersensitivity reactions to the drug, and its safety for pregnant and nursing mothers has not been fully established.
Reference: Clinical Trial "Safety and Efficacy of Natalizumab in the Treatment of Multiple Sclerosis" Study ID Numbers: C-1801 ClinicalTrials.gov Identifier: NCT00027300 Health Authority: United States: Food and Drug Administration