Another Tysabri patient has developed progressive multifocal leukoencephalopathy (PML), an often fatal brain disease. Just three months ago, Biogen Idec said two additional patients had contracted PML.
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. People with a weakened immune system or people taking drugs that suppress their immune system (immunosuppressants) are most likely to get the disease. Symptoms include vision problems, loss of coordination, and memory loss. Patients who survive the disease are often permanently disabled.
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.
In August, Biogen Idec announced that Tysabri had been associated with two other cases of PML, this time among patients taking it in Europe. One patient had been taking Tysabri for 14 months and the other for 17.
The most disturbing aspect of the latest PML cases is that all of patients had been taking Tysabri as monotherapy – with no other drugs. It had been theorized that patients contracting PML had done so because of exposure to multiple medications and that monotherapy with Tysabri was less risky.
In August, the U.S. Food & Drug Administration (FDA) said it was working with Elan and Biogen Idec, the manufacturers of Tysabri, to amend the product labeling to inform prescribers and patients that cases of PML have occurred in patients taking Tysabri as monotherapy.