Medication adherence and health outcomes in persons with multiple sclerosis treated with dimethyl fumarate

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system that particularly affects people in their 30s. Oral disease-modifying therapy (DMT) offers a simple dosage form, good efficacy and safety. Dimethyl fumarate (DMF) is a frequently prescribed oral DMT medication worldwide. The aim of this study was to evaluate the impact of medication adherence on health outcomes in Slovenian persons with MS treated with DMF.

Our retrospective cohort study included persons with relapsing-remitting MS on DMF treatment. The medication adherence was evaluated by AdhereR software package using the proportion of days covered (PDC) measure. The threshold was set at 90%. Health outcomes after treatment initiation were represented by relapse occurrence, disability progression and occurrence of active (new T2 and T1/Gadolinium (Gd) enhancing) lesions between first two outpatient visits and first two brain magnetic resonance imaging (MRI), respectively. For each health outcome a separate multivariable regression model was built.

The study included 164 patients. Their mean age (SD) was 36.7 (8.8) years, and the majority of patients were women (114 or 70%). Eighty-one patients were treatment naive. The mean (SD) PDC value was 0.942 (0.08) and 82% of patients were considered adherent above the 90% threshold. Older age (OR 1.06 per one year, P = 0.017, 95% CI (1.01-1.11)) and treatment naivety (OR 3.93, P = 0.004, 95% CI (1.64-10.4)) were related to higher adherence. In the 6-year follow-up period after DMF treatment initiation, 33 patients experienced a relapse. Among those, 19 required an emergency visit. Sixteen patients had a 1-point disability progression on the Expanded Disability Status Scale (EDSS) score between two consecutive outpatient visits. Thirty-seven patients were found to have active lesions between first and second brain MRI. Medication adherence showed no impact on relapse occurrence or disability progression. Lower medication adherence (10% lower PDC) was associated with higher occurrence of active lesions (OR 1.25, P=0.038, 95% CI: 1.01-1.56). Higher disability prior to DMF initiation was related to a higher risk for relapse occurrence and EDSS progression.

Our study showed high medication adherence among Slovenian persons with relapse-remitting MS on DMF treatment. Higher adherence was associated with lower incidence of the radiological progression of MS. Interventions for improving medication adherence should be intended for younger patients with higher disability prior treatment with DMF and those switching from alternative DMTs.