On August 25, 2008, the Food and Drug Administration (FDA) said it is working with Tysabri manufacturers to update the multiple sclerosis drug’s label after receiving two reports of patients diagnosed with a serious brain infection.

The agency received information about two cases of progressive multifocal leukoencephalopathy (PML) in European Tysabri patients, both of whom had been taking Tysabri for more than one year. Several years ago, Tysabri was withdrawn from the US market after three patients developed the same infection, which is usually fatal.

Authorities allowed the reintroduction of Tysabri under a safety program that prohibits patients from taking it together with other drugs that may also weaken the immune system. The two new patients who contracted the infection, however, were taking only Tysabri.

Biogen Idec and Elan Corp are working with the FDA to update Tysabri’s label to include information about the new cases of PML.

Sources: Jacob Goldstein, “FDA takes news of Tysabri-related infections in stride,” Wall Street Journal, August 26, 2008; “Information for Healthcare Professionals Natalizumab Injection for Intraveneous Use (marketed as Tysabri),” Food and Drug Administration InfoSheet, August 25, 2008.