Objectives To evaluate the efficacy and safety of 2 years of treatment with intramuscular interferon beta-1a (IM IFN beta-1a) in Japanese patients with relapsing-remitting multiple sclerosis, with an exploratory analysis of the impact of initial dose titration on tolerability. Methods Japanese patients with relapsing-remitting multiple sclerosis were randomized to receive IM IFN beta-1a at dosages of either 30 mcg once weekly (full-dose group, n=50) or 15 mcg once weekly for 2 weeks then 30 mcg once weekly thereafter (titration group, n=50). Key outcomes included annualized relapse rate (ARR) at 2 years (primary endpoint), change in disability measured using the Expanded Disability Status Scale (EDSS), safety, and tolerability. Results The ARR (95% CI) decreased from 1.540 (1.381-1.718) at baseline to 0.371 (0.240-0.571) at Year 1 and 0.351 (0.244-0.503) at Year 2. EDSS improvements were apparent from Week 24; the mean change from baseline EDSS score (2.1) at Year 2 was -0.34 (P=0.004). The most frequently reported adverse events were influenza-like illness (92%), nasopharyngitis (57%), relapse of multiple sclerosis (51%), and injection-site reaction (30%). The overall incidence and severity of influenza-like symptoms were similar in the full-dose group and titration group; only 1 participant, in the full-dose group (2%), experienced severe influenza-like symptoms. However, the incidence of influenza-like symptoms was slightly reduced at earlier timepoints in the titration group. Conclusions The results of this 2-year study demonstrate that IM IFN beta-1a can be used effectively and safely in Japanese patients with relapsing-remitting multiple sclerosis for an extended period of time.
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