Safety and Efficacy of Natalizumab in Japanese Patients with Relapsing-Remitting Multiple Sclerosis: Open-Label Extension Study of a Phase 2 Trial

Introduction The efficacy of natalizumab was evaluated in Japanese patients with relapsing-remitting multiple sclerosis (RRMS) in a 24-week, phase 2 bridging study. An open-label, 2-year extension study from this trial was conducted to assess the safety and efficacy of natalizumab treatment in Japanese patients. Methods A total of 97 patients (43 previously on placebo; 54 previously on natalizumab) who had completed the bridging study were treated with 300 mg natalizumab every 4 weeks. Multiple sclerosis relapses, changes in Expanded Disability Status Scale (EDSS) scores, and adverse events were assessed at regular intervals. Anti-natalizumab and anti-JC virus (JCV) antibodies were measured. Results After 2 years of natalizumab treatment, the mean adjusted annualized relapse rate was 0.30 (95% confidence interval [CI]: 0.18–0.52) among previously-on-placebo patients and 0.13 (95% CI: 0.05–0.29) among previously-on-natalizumab patients. The mean change in EDSS score from baseline to week 120 was −0.03 among previously-on-placebo patients and −0.18 among previously-on-natalizumab patients. In both groups, >90% of patients experienced ≥1 adverse event. Two previously-on-placebo patients developed persistently positive anti-natalizumab antibodies. Approximately 65% of all patients tested positive for anti-JCV antibodies at open-label treatment initiation. No deaths or progressive multifocal leukoencephalopathy cases were reported. Conclusions The efficacy and safety findings from this 2-year open-label extension study are comparable to and confirm the results of other clinical trials of natalizumab conducted in non-Asian patient populations, and provide longer-term evidence of efficacy and safety in Japanese patients. Trial registration ClinicalTrials.gov identifier NCT01416155. Funding Biogen.