The European Medicines Agency Pharmacovigilance Risk Assessment Committee (PRAC), responsible for assessing and monitoring safety issues for human medicines, completed a review on the risk for progressive multifocal leukoencephalopathy (PML) in multiple sclerosis (MS) patients treated with the medicine Tysabri (natalizumab). The issued guidelines have the objective of minimizing patients’ risk.
Recently, a study titled “Therapy with natalizumab is associated with high JCV seroconversion and rising JCV index values,” published in the online issue of the journal Neurology, Neuroimmunology and Neuroinflammation, reported that MS patients treated with Tysabri (natalizumab) have an increased risk of developing high levels of antibodies associated with a virus that can cause the rare, but very serious, brain infection PML.
They said early detection and treatment of PML, in the asymptomatic stages of the disease, were shown to be crucial for limiting the degree of brain damage and disability.
Hence, since asymptomatic cases of PML are easily detected through magnetic resonance imaging (MRI) scans, PRAC recommends more frequent MRI scans (every three to six months) in patients at higher risk of PML, namely MS patients who have antibodies against John Cunningham virus (a sign that a person has been exposed to the virus), are undergoing treatment with Tysabri for at least two years, and were submitted to previous immunosuppressant medicines before starting on Tysabri. All three factors, once present in the same patient, establish them at a higher risk for PML development.
Results from clinical trials suggested that the risk for PML is small, and even lower than previously estimated: antibody index values of 0.9 or less, increasing significantly in patients with index values above 1.5 who are undergoing treatment with Tysabri for longer than two years. Considering these results, the PRAC guidelines note that patients at higher risk of PML have a high antibody index and are undergoing Tysabri treatment for more than two years.
PRAC recommends that in patients at higher risk of developing PML, Tysabri treatment should be carefully evaluated and the medication only continued if patient benefits clearly outweigh the risks. Patients with a low antibody index and no use of immunosuppressant drugs before initiating Tysabri should also be carefully monitored, and undergo an antibody test every six months after they have been on Tysabri therapy for a period longer than two years.
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