Effectiveness of interferon beta treatment in relapsing-remitting multiple sclerosis: an Italian cohort study.

Randomized clinical trials (RCTs) have provided evidence for the efficacy of interferon beta (IFNbeta) in the treatment of relapsing-remitting multiple sclerosis (RRMS). The aim of this study was to evaluate the effectiveness of IFNbeta treatment in clinical practice.This was a national, multicentre, observational study of patients with confirmed RRMS. Demographic, clinical and therapeutic data were retrospectively collected for each patient enrolled in the study.The study cohort consisted of 427 patients exposed to and 245 never exposed to IFNbeta treatment during the study period (for a total 2297 patient-years of follow-up). Among the exposed patients, 215 were initially untreated and then began IFNbeta later in the follow-up period; 137 of these patients were exposed to IFNbeta for more than 2 years. In these patients, IFNbeta treatment reduced the mean relapse rate by 24.2\%[95\% confidence interval (CI): 5.8-42.5\%]. For 640 of the 672 patients enrolled in the study, it was possible to calculate the area under the disability/time curve compared to that present at baseline. A total of 117 (18.3\%) patients displayed disability progression. Adjustment of the disability progression rates for potential confounders and/or for propensity scores by Poisson regression model resulted in relative risks for patients exposed to IFNbeta treatment compared to those never exposed to IFNbeta of 0.87 (95\% CI: 0.56-1.34) after an exposure of < or = 2 years, and of 0.35 (95\% CI: 0.21-0.60) after an exposure of >2 years.These findings suggest that the evidence from RCTs on the treatment of RRMS with IFNbeta has been effectively translated into routine clinical practice.