Interferon β-1a in relapsing multiple sclerosis:: four-year extension of the European IFNβ-1a Dose-Comparison Study

Background: Multiple sclerosis ( MS) is a chronic disease requiring long-term monitoring of treatment. Objective: To assess the four-year clinical efficacy of intramuscular (IM) IFNbeta-1a in patients with relapsing MS from the European IFNbeta-1a Dose-Comparison Study. Methods: Patients who completed 36 months of treatment ( Part 1) of the European IFNbeta-1a Dose-Comparison Study were given the option to continue double-blind treatment with IFNbeta-1a 30 mcg or 60 mcg IM once weekly (Part 2). Analyses of 48-month data were per formed on sustained disability progression, relapses, and neutralizing antibody (NAb) formation. Results: Of 608/802 subjects who completed 36 months of treatment, 493 subjects continued treatment and 446 completed 48 months of treatment and follow-up. IFNbeta-1a 30 mcg and 60 mcg IM once weekly were equally effective for up to 48 months. There were no significant differences between doses over 48 months on any of the clinical endpoints, including rate of disability progression, cumulative percentage of patients who progressed (48% and 43%, respectively), and annual relapse rates; relapses tended to decrease over 48 months. The incidence of patients who were positive for NAbs at any time during the study was low in both treatment groups. Conclusion: Compared with 60-mcg IM IFNbeta-1a once weekly, a dose of 30 mcg IM IFNbeta-1a once weekly maintains the same clinical efficacy over four years.