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TYSABRI is a prescription medicine approved for adult patients with relapsing forms of MS to slow the worsening of disability and decrease the number of flare-ups (relapses). Because TYSABRI increases the risk of progressive multifocal leukoencephalopathy (PML), a rare brain infection that usually causes death or severe disability, TYSABRI is generally recommended for patients that have not been helped enough by, or cannot tolerate, another treatment for MS. TYSABRI does not cure MS and has not been studied for longer than two years or in patients with chronic progressive MS.
Natalizumab is a humanized monoclonal antibody against the cell adhesion molecule α4-integrin. Natalizumab is used in the treatment of multiple sclerosis and Crohn's disease. It is co-marketed by Biogen Idec and Élan as Tysabri, and was previously named Antegren. The drug is believed to work by reducing the ability of inflammatory immune cells to attach to and pass through the cell layers lining the intestines and blood–brain barrier. Natalizumab has proven effective in treating the symptoms of both diseases, preventing relapse, vision loss, cognitive decline and significantly improving quality of life in people with multiple sclerosis, as well as increasing rates of remission and preventing relapse in Crohn's disease.