Tysabri (Natalizumab) is a prescription drug co-marketed by Biogen Idec and Élan as Tysabri. It was previously named Antegren. Natalizumab is administered by infusion every 28 days and is used in the treatment of multiple sclerosis and Crohn's disease. In combination with interferon beta-1a the drug has also been linked to two cases of progressive multifocal leukoencephalopathy, one of which was fatal. 114634 Tysabri Tysabri Natalizumab 538 A synthetic version of naturally occuring interferons that have immunomodulatory, antiviral and antiproliferative activities. It may exert antitumor activity by anti-angiogenic and cell differentiation activities. (NCI) 32819 Interferon Beta-1a Interferon Beta-1a Interferon Beta-1A Avonex Rebif Interferon Beta 1a INTERFERON BETA-1A Interferon-Beta-1A BG9418 Recombinant Interferon Beta-1a 551