Background/objective: Differences in patient adherence to various disease-modifying drugs (DMDs) in the treatment of multiple sclerosis (MS) are not well understood. The goal of this study was to evaluate adherence of adult MS patients in Ontario with public drug plan coverage to various DMDs: intramuscular interferon beta-1a (i.m. IFNβ-1a, Avonex), subcutaneous interferon beta-1a (s.c. IFNβ-1a, Rebif), subcutaneous interferon beta-1b (IFNβ-1b, Betaseron) or glatiramer acetate (Copaxone).
Methods: In this retrospective cohort study, Ontario Public Drug Plan beneficiaries aged 15 or older who were newly treated with i.m. IFNβ-1a, s.c. IFNβ-1a, IFNβ-1b or glatiramer acetate between April 2006 and March 2008 were followed forward until treatment discontinuation, switch to another DMD or a maximum two year follow-up period. Cumulative persistence rates were analyzed by the Kaplan-Meier method. The proportion of patients reaching the study endpoints after the two year follow-up period was also calculated.
Results: Cumulative persistence rates for all four DMDs were similar over time (p=0.80), ranging from 73.6-79.1% at six months, 59.1-63.1% at one year and 41.5-47.4% at two years. After two years, the proportion of patients who had discontinued treatment, switched to another DMD or died was similar among DMDs (p=0.79, Fisher's exact test). Switching between DMD types was low and occurred in 3.4-6.5% of new DMD users.
Conclusions: Adherence to DMDs in adult MS patients in Ontario is poor, which is consistent with previously reported adherence rates to MS DMDs in other regions. No significant differences in adherence exist between the DMDs evaluated in this study.