title: Estimating long-term effects of disease-modifying drug therapy in multiple sclerosis patients.
abstract: Two methods were used to estimate the long-term impact of disease-modifying drug therapy (DMDT) in patients with relapsing multiple sclerosis (MS) who completed a placebo-controlled, randomized clinical trial of interferon beta-1a (IFNbeta-1a). The study cohort consisted of patients with ambulatory relapsing MS who had previously participated in a placebo-controlled clinical trial for two years. At its end, patients were managed in an unstructured fashion by their neurologists and re-evaluated at an average of 6.1 years after the end of the trial. Follow-up evaluation was obtained for 93% of the 172 eligible patients. Because study inclusion criteria required that all patients have an Expanded Disability Status Scale (EDSS) score of < or = 3.5 at entry, disability progression at follow-up was defined as EDSS > or = 6.0. Two methods were used to estimate the expected proportions that reached EDSS > or = 6.0 at follow-up. Estimates were compared with observed proportions. Method 1 used progression rates observed during the two-year phase III clinical trial and the percentage of time that patients were on DMDT during the follow-up period. Method 2 used progression rates from a natural history comparison group of relapsing-remitting MS patients. At the eight-year follow-up, 42.0% of the original placebo patients and 29.1% of the original IFNbeta-1a patients reached an EDSS > or = 6.0, an observed treatment effect of approximately 30%. Using method 1, it was estimated that 36.3% of the original placebo patients and 27.6% of the original IFNbeta-1a patients should have reached an EDSS > or = 6.0. Use of the natural history control group (method 2) predicted less plausible outcomes. Estimated proportions of patients reaching the endpoint were 63.3% for the original placebo group and 55.8% for the original IFNbeta-1a group. Treatment effect sizes of 75-90% would be required to match estimates from method 2 with the observed outcome. The paucity of data on the long-term treatment of patients with MS may be aided by applying these or similar methods to vigorously followed cohorts of patients.
authors.affiliation: Department of Neurology, Mellen Center for Multiple Sclerosis Treatment and Research, The Cleveland Clinic Foundation, OH 44195, USA. rudickr@ccf.org
authors.forename: R A
authors.initials: RA
authors.lastname: Rudick
authors.forename: G R
authors.initials: GR
authors.lastname: Cutter
authors.forename: M
authors.initials: M
authors.lastname: Baier
authors.forename: B
authors.initials: B
authors.lastname: Weinstock-Guttman
authors.forename: M K
authors.initials: MK
authors.lastname: Mass
authors.forename: E
authors.initials: E
authors.lastname: Fisher
authors.forename: D M
authors.initials: DM
authors.lastname: Miller
authors.forename: A W
authors.initials: AW
authors.lastname: Sandrock
mesh_terms: D000276:Adjuvants, Immunologic / Q000627:therapeutic use*; D004185:Disability Evaluation; D018450:Disease Progression; D005500:Follow-Up Studies; D006801:Humans; D000068556:Interferon beta-1a; D016899:Interferon-beta / Q000627:therapeutic use*; D015233:Models, Statistical; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000188:drug therapy* / Q000503:physiopathology; D016032:Randomized Controlled Trials as Topic / Q000379:methods*
chemical_list: D000276:Adjuvants, Immunologic; D016899:Interferon-beta; D000068556:Interferon beta-1a