[Natalizumab in multiple sclerosis: the second treatment revolution].

Natalizumab (Tysabri) is the first monoclonal antibody indicated for the treatment of active relapsing-remitting multiple sclerosis. Natalizumab is reserved for hospital use. Strict monitoring is necessary to detect side effects associated with the perfusion of the product, possible inefficacy of the treatment, and, more rarely, infectious complications, some of which (for example, progressive multifocal leukoencephalitis) are severe. Rigorous collection of efficacy and tolerance data will make it possible to assess the impact of this treatment on the natural history of multiple sclerosis.