* The label of natalizumab (Tysabri), an immunosuppressant used in the treatment of relapsing forms of multiple sclerosis and moderate-to-severe Crohn's disease, has been revised to highlight the recent discovery that the presence of anti–John Cunningham virus (JCV) antibodies increases the risk of progressive multifocal leukoencephalopathy (PML).
* A newly approved blood test can be used to determine the presence of anti-JCV antibodies.
* PML has also been reported with brentuximab vedotin (Adcetris), an intravenously administered monoclonal antibody used to treat lymphoma.
Diane S. Aschenbrenner is the course coordinator for undergraduate pharmacology at Johns Hopkins University School of Nursing in Baltimore, MD. She also coordinates Drug Watch: firstname.lastname@example.org.