To Örebro University

Introduction: Dimethyl fumarate (DMF) is an oral therapy for relapsing multiple sclerosis (RMS). DMF is included in the Swedish post-market surveillance study “Immunomodulation and Multiple Sclerosis Epidemiology” (IMSE).

Objectives/Aims: To assess the effectiveness and safety of DMF with focus on patients treated at least 72 months.

Methods: Descriptive data of Extended Disability Status Scale (EDSS), Multiple Sclerosis Severity Scale (MSSS), Symbol Digit Modalities Test (SDMT), Multiple Sclerosis Impact Scale (MSIS-29) and Adverse Events (AEs) is obtained from the nationwide Swedish Neuro Registry (NeuroReg). Effectiveness measures were assessed using the paired samples T-test.

Results: 2843 DMF-treated patients were included between March 2014 and March 2024 with a mean treatment duration of 43 months and 72% of patients having discontinued treatment at least once. The main reasons for discontinuation were AEs (42%) and lack of effect (32%). 211 AEs were reported to the Medical Products Agency in Sweden of which 66 were serious. For both serious and non-serious AEs reported, gastrointestinal disorders were the most common (18% and 27%, respectively).

657 patients had continuous treatment for at least 72 months. This cohort had a mean age of 43 years and a mean treatment duration of 99 months. The majority (59%) had switched from interferon or glatiramer acetate and 31% were treatment naïve.

Significant improvements in mean values at 72 months of treatment compared to baseline were noted for MSSS and MSIS-29 Psychological (p<0.05). All other tests remained stable after 6 years of treatment. The Annual Relapse Rate (ARR) decreased significantly during treatment compared to one year prior to treatment start.

141 patients (21%) have discontinued DMF treatment in the 72-month cohort. The main reasons for discontinuation were lack of effect (38%), other reasons (25%) and AEs (18%).

Conclusion: DMF demonstrates clinical improvements and/or stability in patients treated ≥ 72 months. However, due to the high discontinuation rate there is an unavoidable selection bias. Continued follow up is needed to assess the effectiveness and safety of DMF over longer time periods in a real-world setting.