Randomised double-blind placebo-controlled study of interferon β-1a in relapsing/remitting multiple sclerosis

Summary Background Previous trials of interferon β in multiple sclerosis (MS) have shown efficacy, but the degree of clinical benefit remains uncertain, and the optimum dose is not known. We undertook a double-blind, placebo-controlled study in relapsing/remitting MS to investigate the effects of subcutaneous interferon β-1a. Methods 560 patients with Kurtzke expanded disability status scale (EDSS) scores of 0–5·0, from 22 centres in nine countries, were randomly assigned subcutaneous recombinant interferon β-1a 22 μg (n=189), or 44 μg (n=184), or placebo (n=187) three times a week for 2 years. Neurological examinations were done every 3 months. All patients had MRI twice yearly and 205 had monthly scans in the first 9 months of treatment. Analysis was by intention to treat. Findings Clinical data on 533 (95%) patients were available at 2 years. The relapse rate was significantly lower at 1 and 2 years with both doses of interferon β-1a than with placebo (mean number per patient 1·82 for 22 μg group, 1·73 for 44 μg group vs 2·56 for placebo group: risk reductions 27% [95% Cl 14–39] and 33 [21–44]). Time to first relapse was prolonged by 3 and 5 months in the 22 μg and 44 μg groups respectively, and the proportion of relapse-free patients was significantly increased (p Interpretation Subcutaneous interferon β-1a is an effective treatment for relapsing/remitting MS in terms of relapse rate, defined disability, and all MRI outcome measures in a dose-related manner, and it is well tolerated. Longer-term benefits may become clearer with further follow-up and investigation.