Natalizumab (Tysabri®)—Re-defining Efficacy in Multiple Sclerosis—Data from Clinical Trials to Post-marketing Experience

Multiple sclerosis (MS) is a chronic, disabling condition with severe clinical and social consequences. Current first-line disease-modifying treatments have limited efficacy and do not halt long-term disease progression in the majority of patients. Natalizumab (Tysabri®) is the only monoclonal antibody licensed for use in relapsing–remitting MS (RRMS). It is regarded by many neurologists as the most effective MS drug on the market today, and has the potential to re-define successful MS therapy. Its efficacy has been demonstrated both in large-scale clinical trials and in post-marketing settings. Beneficial effects include reduction of relapse rates and disease progression, as well as magnetic resonance imaging (MRI) measures of disease activity. Natalizumab treatment has a substantial impact on patient quality of life. Moreover, patients have shown significant improvement following natalizumab treatment, making continuing clinical remission a realistic goal in MS for the first time. However, the benefits of natalizumab must be balanced against risk. Progressive multifocal leukoencephalopathy (PML) is a rare event associated with natalizumab treatment that may be minimized with a ri