Safety Alerts & Recalls

What does this mean?

Tysabri continues to be an effective treatment for multiple sclerosis (MS) and Crohn's disease. However, because of the risk of PML, it is important for you to regularly speak with your doctor and weigh the benefits and risks of Tysabri in your specific situation.

Because prior exposure to JCV can increase your risk of developing PML, your healthcare professional may recommend a blood test to see if you have ever been exposed to JCV, the virus that causes PML. This test measures antibodies to the virus, which are often referred to as "anti-JCV antibodies." The risk of developing PML increases if you have tested positive for anti-JCV antibodies and have one or two of the other known risk factors. If you have received treatment with Tysabri for a significant period of time or if you have received treatment with certain medicines that can weaken a patient’s immune system before receiving Tysabri, please be sure to talk to your doctor about how these factors may affect your treatment with Tysabri.

If you have any questions or concerns about Tysabri and the risk of PML, please follow with your healthcare professional.

Healthcare providers and patients are encouraged to report side effects related to the use of medicines to the FDA's MedWatch Program by telephone at 1-800-332-1088, by fax at 1-800-332-0178, by mail at MedWatch, FDA, 5600 Fishers Lane, Rockville, MD 20852-9787, or on the MedWatch website at

FDA Announces New Risk Factor for Progressive Multifocal Leukoencephalopathy (PML) Associated with Tysabri (Natalizumab)

The U.S. Food and Drug Administration (FDA) is informing the public that testing positive for anti-JC virus (JCV) antibodies has been identified as a risk factor for progressive multifocal leukoencephalopathy (PML). PML is a rare but serious brain infection associated with use of Tysabri (natalizumab) for the treatment of multiple sclerosis (MS) or Crohn's disease.

The John Cunningham virus (JCV) is a common virus that many people have been exposed to at some point in their lives, and is generally harmless. However, people with weakened immune systems, such as patients using therapies like Tysabri, have an increased chance of developing PML from JCV.

A patient's anti-JCV antibody status may be determined by using an anti-JCV antibody detection test, recently approved by the FDA, that is ordered by a healthcare professional. Testing positive for anti-JCV antibodies means that a person has been exposed to JCV in the past.

Currently, there is no treatment, prevention, or cure for PML, and no certain way to predict who will develop it. This new anti-JCV antibody detection test together with assessing other risk factors will allow the physicians and patients to carefully assess the risks and benefits of continuing Tysabri treatment depending on the complete clinical information for the particular patient. The following risk factors have been identified that increase the chance of Tysabri-treated patients developing PML: • the presence of anti-JCV antibodies, which reflects prior exposure to JCV

• treatment with Tysabri for a significant period of time (longer than 2 years)

• treatment with certain medicines that can weaken a patient’s immune system (immunosuppressants such as mitoxantrone, azathioprine, methotrexate, cyclophosphamide, and mycophenolate mofetil) before receiving Tysabri.

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Source: FDA
Publication Date: 2012-01-24
Last Updated: 2012-01-24

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