JC Virus in Natalizumab Users: Test for Virus Exposure Approved

Patients with multiple sclerosis (MS) or Crohn disease who are taking natalizumab face an increased risk for progressive multifocal leukoencephalopathy (PML) if they have been exposed to JC virus, the FDA warned in January. The agency also announced approval of a new blood test to detect JC virus antibodies.

JC virus is common and usually harmless, the agency said, but its presence can be dangerous in patients taking immunomodulating drugs like natalizumab. Other risk factors associated with developing PML while on natalizumab are treatment with natalizumab for longer than 2 years and previous treatment with immunosuppressant drugs such as methotrexate or cyclophosphamide (but not prior use of first-line injectable immunomodulatory agents, i…