New Tysabri PML Risk Factor Identified

The Food and Drug Administration has identified a new risk factor which could lead to the life-threatening brain infection known as progressive multifocal leukoencephalopathy (PML) associated with the use of the drug Tysabri.

Tysabri is prescribed as a “last resort” in the treatment of Multiple Sclerosis (MS) and was also an off-label treatment of Crohn’s disease. It is often prescribed for “relapsing forms” of MS, according to the FDA. It is widely considered a dangerous prescription drug that carries a risk of numerous serious side effects.

On Jan. 20, the FDA approved the anti-JC antibody test which helps identify a patient who has been exposed previously to the John Cunningham virus (JCV). The test is known as Stratify JCV Antibody ELISA test2. If a patient tests positive during that procedure it is an indication they’ve been exposed to the virus.

Patients previously exposed to JCV puts them at risk of developing PML, especially while taking Tysabri. In its Drug Safety Communication issued recently, the FDA said there are now three known risk factors associated with PML, with JCV exposure being the latest. A patient exhibiting all three risk factors face a serious risk of developing PML, determining that risk to be 11 in 1,000 patients.

Prescribing physicians and patients are being advised to carefully consider the possible benefits of taking Tysabri. While JCV is typically considered a non-serious virus, people taking Tysabri have had their immune systems weakened and this causes a greater risk of developing PML, for which there is no known treatments or cures and typically results in death or severe disability.

The FDA admits there is “no certain way” to determine who will develop PML.

In addition to the presense of JCV, the FDA has identified two other risk factors which are known to increase the risk of PML: taking Tysabri for more than two years or taking other immunosuppressant drugs like mitoxantrone, azathioprine, methotrexate, cyclophosphamide and mycophenolate before taking Tysabri.

The FDA announced at the same time that it is updating the safety labels of Tysabri to note the benefit of the JCV test and that the presence of JCV in a patient taking Tysabri is a risk factor in that person developing PML. The agency said the JCV test should not be administered “alone” nor should it be used to test for PML.

In addition to this risk of the life-threatening PML, Tysabri has been linked in the past to severe liver damage. Patients taking Tysabri for as little as a week face a risk of severe liver damage. The FDA has identified patients suffering from jaundice or other previous liver injuries as those who should not be prescribed Tysabri.

Just a few months after approving Tysabri as an off-label treatment of moderate-to-severe forms of Crohn’s disease, the agency also noted that some studies have associated use of the drug to the development of melanoma skin cancer.

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