Randomised double-blind placebo-controlled study of interferon beta-1a in relapsing/remitting multiple sclerosis. PRISMS (Prevention of Relapses and Disability by Interferon beta-1a Subcutaneously in Multiple Sclerosis) Study Group.

BACKGROUND: Previous trials of interferon beta 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 beta-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 beta-1a 22 microg (n=189), or 44 microg (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 beta-1a than with placebo (mean number per patient 1.82 for 22 microg group, 1.73 for 44 microg group vs 2.56 for placebo group: risk reductions 27% [95% CI 14-39] and 33 [21-44]). Time to first relapse was prolonged by 3 and 5 months in the 22 microg and 44 microg groups respectively, and the proportion of relapse-free patients was significantly increased (p<0.05). Interferon beta-1a delayed progression in disability, and decreased accumulated disability during the study. The accumulation of burden of disease and number of active lesions on MRI was lower in both treatment groups than in the placebo group.

INTERPRETATION: Subcutaneous interferon beta-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.