A medication used to treat multiple sclerosis (MS) and Crohn’s disease has been linked to a serious and usually fatal neurological disorder, according to an alert issued to neurological health care professionals and their patients by the Food and Drug Administration (FDA).
Natalizumab, marketed as Tysbri, was approved by the FDA in 2004 to treat relapsing forms of MS. In 2008, the FDA approved the drug’s use for moderately to severely active Crohn’s disease. From July 2006, when Tysabri marketing resumed, to September 8, 2009, there were 13 reported cases of Tysabri-related progressive multifocal leukoencephalopathy (PML) confirmed worldwide in patients being treated for MS. There have been no reports of PML in patients with Crohn’s disease.
PML is a rare and usually fatal viral disease. Symptoms include headaches, loss of coordination, loss of language ability, memory loss, vision problems, and weakness of the legs and arms that gets worse over time. The JC virus that causes the disease is widespread. About 86 percent of the general population have it, but the virus usually remains latent, causing disease only when the immune system has been severely weakened.
Based on the available data of patients who have been treated with Tysabri, the risk of developing PML appears to increase with the number of Tysabri infusions received. The rate among patients who have received at least 24 infusions is between 0.4 to 1.3 per 1,000 patients.
The FDA is requiring changes to Tysabri prescribing information or to the Tysabri risk management plan. Patients who have experienced any adverse reactions with this drug should contact their doctor and report the problem to the FDA MedWatch program.