Medication persistence among people with multiple sclerosis in Slovenia treated with dimethyl fumarate

Multiple sclerosis is a chronic, demyelinating inflammatory disease of the central nervous system. Medication persistence is defined as an interval between the initiation and last dose of the applied medication and presents a useful surrogate marker of a stable disease course. This observational study aimed to evaluate medication persistence and discontinuation reasons in Slovenian people with multiple sclerosis treated with dimethyl fumarate.

Our retrospective cohort study evaluated people with relapsing-remitting multiple sclerosis treated with dimethyl fumarate as an initial monotherapy or switched from injectable disease-modifying therapy medication between 2014 and 2021. Medication dispenses were extracted from the Slovenian National Institute of Public Health Outpatient Medication Database. The medication persistence criterion was based on the treatment gap. Patients exceeding a 60-day gap were considered nonpersistent. The median time to discontinuation was assessed using survival analyses. Considering discontinuation reasons, patients were further divided into safety and inefficacy groups. Due to the high probability of adverse effects, patients exceeding a 60-day gap were included in the safety group, but definite discontinuation reason remains unknown. The impact of covariates was evaluated by Cox regression.

A total of 269 patients were included (183 women, mean age 37 years). During the 7-year follow-up period, 123 (45.7%) patients discontinued treatment. The median time to discontinuation was 5.6 years. After 1, 2, and 5 years of treatment, 84%, 77%, and 57% of patients were found to be persistent, respectively. All patients older than 30 years (p = 0.0013) and among them, those in the inefficacy group (p = 0.037) were more likely to be persistent.

The results of our study proved a high persistence rate among our patients. The most frequent discontinuation reason was gastrointestinal adverse effects. Medication persistence requires interventions in younger patients with an unstable disease course.