Skip to navigation Skip to content



FDA Updates Tysabri Label to Include Lab Test that Helps Identify Person’s Risk of Developing PML

January 23, 2012

The U.S. Food and Drug Administration has approved a change to the prescription label for Tysabri®  (natalizumab, Biogen Idec and Elan) to show that a laboratory test that detects antibodies to the JC virus can help determine a person’s risk of developing PML, a severe brain infection. This virus is responsible for PML, which has emerged in some people who have taken Tysabri. (Read more about natalizumab and PML.) The availability of the lab test should enhance the ability of people with MS and their physicians to weigh risks and benefits of this therapy. Read the FDA's announcement

The presence of antibodies indicates that a person has at some point been infected by or exposed to the virus, which usually lies dormant. In studies of patients who have developed PML on Tysabri, all of those for whom test results were available had serum antibodies prior to the onset of PML. Based on research findings, patients who have a positive antibody test are at higher risk of developing PML. Previous findings have also shown that prior use of immune-suppressing drugs and taking Tysabri for more than two years each increase a person’s risk for developing PML.

The revised label suggests that the risks and benefits of starting or continuing Tysabri should be carefully considered in patients found to be antibody positive and have one or more additional risk factors. Those found to be antibody positive, have used Tysabri for less than two years, and have no prior use of immune suppressing drugs are estimated to have a risk of PML of less than 1/1000; those with all three known risk factors have an estimated risk of PML of 11/1000.

The FDA’s announcement stresses that patients who test negative for anti-JCV antibodies are still at risk for the development of PML due to the potential for a new JCV infection or a false negative test result. It also notes that doctors should consider testing patients prior to treatment or during treatment if antibody status is unknown. UPDATE: On August 15, 2012, the FDA required another change to the prescribing information, recommending that patients with a negative anti-JCV antibody test result should be retested every 6 months.

“This label change marks an important advance in assisting people with MS and their physicians to make better-informed decisions concerning the challenges of balancing effectiveness with safety,” commented Nicholas LaRocca, PhD, vice president of health care delivery and policy research at the National MS Society.

The lab test, called STRATIFY JCV, is available from Quest Diagnostics.


About Multiple Sclerosis

Multiple sclerosis is an unpredictable, often disabling disease of the central nervous system. Symptoms range from numbness and tingling to blindness and paralysis, and there is currently no cure for MS. The progress, severity and specific symptoms of MS in any one person cannot yet be predicted, but advances in research and treatment are leading to better understanding and moving us closer to a world free of MS. An estimated 1 million people live with MS in the United States. Most people with MS are diagnosed between the ages of 20 and 50, and it affects women three times more than men.


© 2023 The National Multiple Sclerosis Society is a tax exempt 501(c)3 nonprofit organization. Its Identification Number (EIN) is 13-5661935.