The Food & Drug Administration (FDA) is updating <"https://www.yourlawyer.com/topics/overview/tysabri">Tysabri safety information to include cases of progressive multifocal leukoencephalopathy or PML, a rare brain infection that some Tysabri patients have developed. However, according to The Wall Street Journal, the agency is not making any changes to the Tysabri label.
In the U.S. Tysabri was taken off the market in 2005 after three patients in clinical trials developed PML. But the drug was reapproved in 2006, although it was subject to restrictions. Tysabri is now available only to patients with relapsing multiple sclerosis (MS) or Crohn’s disease (CD) who are enrolled in the risk minimization plan called the TOUCH Prescribing Program. Under the TOUCH Prescribing Program, every Tysabri-treated patient is closely monitored and followed for the occurrence of PML and other serious opportunistic infections.
PML attacks the brain and central nervous system and is usually fatal. It is caused by a polyomavirus, called the JC virus. The JC virus is often acquired during childhood. Most adults have been infected with the JC virus but do not develop PML. The virus appears to remain inactive until something (such as a weakened immune system) allows it to be reactivated and start to multiply. Symptoms include vision problems, loss of coordination, and memory loss. Patients who survive the disease are often permanently disabled.
According to The Wall Street Journal, the FDA
says that the overall rate of Tysabri patients developing PML remains below the one-in-1,000 rate implied on the label. However, the agency warned that this risk “appears to increase with the number of Tysabri infusions received” and that the average number of infusions received before the diagnosis of PML was 25. The rate of PML in patients who have received at least 24 Tysabri infusions ranges from 0.4 to 1.3 per 1,000 patients, the FDA said.
People with a weakened immune system or people taking drugs that suppress their immune system (immunosuppressants) are most likely to get PML. Over the summer, we reported that the FDA was looking into a link between the lymphoma drug, Rituxan, and the disease. In April, the psoriasis drug Raptiva was voluntary withdrawn from the market after three patients died from PML.
