OBJECTIVES: To explore the relationship between medication-use patterns of multiple sclerosis (MS) disease-modifying therapy (DMT) and relapse in a real-world setting. METHODS: This was a retrospective, observational study using administrative claims data. Dimethyl fumarate (DF), a DMT, was selected for analysis due to availability of medication-dosing data in relation to efficacy observed in a clinical trial. Adult MS patients with DF claims (March 2013–January 2014) continuously enrolled for 9 months before and after therapy initiation were included. A validated algorithm was used to define relapse by either an inpatient claim with a primary MS diagnosis or a systemic corticosteroid claim within 7 days of an MS outpatient visit. Medication-use patterns were assessed by non-adherence (medication possession ratio (MPR) <0.90), suboptimal average daily dose (ADD <360 mg/day), and treatment non-persistence (DMT switch or ≥30-day gap in therapy). The ADD cut-point was based on the ineffectiveness of DF in reducing the number of new brain lesions at doses <360 mg/day. RESULTS: The study sample consisted of 2,879 patients; 19.8% relapsed within 9 months, with an average time to relapse of 110 days (standard deviation: 77.9). A higher proportion of non-adherent patients relapsed versus adherent patients (23.4% vs. 17.9%; p=0.0004). A higher proportion of patients with suboptimal ADD experienced relapse compared with those with ADD ≥360 mg/day (26.7% vs. 17.9%, p<0.0001). Non-persistence was associated with a higher occurrence of relapse compared with persistence (25.0% vs. 18.2%, p=0.0001).  CONCLUSIONS: Non-adherence and suboptimal dosing with DF were related to higher relapse rates in MS patients in a real-world setting. Further research is needed to confirm these findings for other DMTs and to quantify the level of non-adherence with its impact on effectiveness. REFERENCES: