Swedish natalizumab (Tysabri) multiple sclerosis surveillance study.

A post-marketing surveillance program was implemented to monitor the safety and open label efficacy of natalizumab since its launch in Sweden August 2006. Patients are registered in the Swedish multiple sclerosis (MS)-registry that has a nationwide coverage using a standardized follow-up that includes EDSS, MSSS, SDMT, MSIS-29, and recording of adverse events (AEs). As of 31 January, 2010, 1,115 patients had been included, of which 363 were treated ≥ 24 months. Dropout rate was 10%, mainly due to planned pregnancy. Serious AEs were rare, but included three cases of progressive multifocal leukoencephalopathy (PML), none of which had received previous immunosuppressive therapy. All analyzed clinical outcome parameters showed significant improvements compared to baseline for patients exceeding 24 months of treatment. Our results demonstrate good general tolerability and sustained efficacy of natalizumab for patients with severe MS, though the risk of PML remains a concern.