Safety and efficacy response to interferon beta-1a therapy in Japanese patients with multiple sclerosis: Interim results of a postmarketing surveillance study

Objectives To evaluate safety and efficacy of intramuscular interferon beta-1a (IFN beta-1a) in Japanese patients with relapsing-remitting multiple sclerosis over the first 2 years of treatment. Methods Safety data were collected from patients registered in a postmarketing surveillance (PMS) study and combined with spontaneous safety reports from other Japanese patients receiving IFN beta-1a. Efficacy, including annualized relapse rate (ARR), was assessed only in patients in the postmarketing surveillance study. Results Safety analyses were based on 2589 patients, and efficacy analyses included 1241 of the 1638 patients registered in the postmarketing surveillance study who had completed 2 years of treatment (mean treatment duration, 598 days). Safety findings were consistent with those seen in clinical trials; the most commonly reported adverse event was fever (9.8%). The ARR decreased by 71% (from 0.95 at baseline, before study enrolment, to 0.28 at the last on-therapy assessment) overall, and by 89% (from 1.22 to 0.14) among the 374 IFN beta-naive patients. Among the 653 patients with relapse data at baseline and at year 2, 401 (61.4%) were classified as responders to intramuscular IFN beta-1a therapy (defined as those with lower ARR at both year 1 and year 2 than at baseline), with an 87% reduction in ARR (from 1.29 at year 1 to 0.17 at year 2). Conclusions The results of this interim analysis are consistent with those of previous studies carried out largely in Caucasian patients, and show the efficacy and safety of intramuscular IFN beta-1a treatment for Japanese patients with multiple sclerosis in clinical practice.