Safety and Effectiveness of Dimethyl Fumarate in Japanese Patients With Multiple Sclerosis: 2‐Year Post‐Marketing Surveillance Data

ABSTRACT Background Dimethyl fumarate (DMF) is an orally administered disease‐modifying drug used for the treatment of multiple sclerosis (MS) in numerous countries worldwide. Aim An ongoing post‐marketing surveillance (PMS) is assessing the real‐world safety and effectiveness of DMF in Japanese patients with MS. Here, we report 2‐year data from this PMS. Methods This interim analysis used data from all patients with MS who were treated with DMF in Japan between February 2017 and March 2024. Safety endpoints included adverse events (AEs) and important identified risks (i.e., progressive multifocal leukoencephalopathy (PML), anaphylaxis, acute kidney injury, hepatic dysfunction, changes in lymphocyte or white blood cell counts, infections other than PML, flushing‐related AEs, and gastrointestinal events). Effectiveness endpoints included annualized relapse rate (ARR) and changes in Expanded Disability Status Scale (EDSS) score. Results Of 2092 patients in the safety analysis (median age 42 years; 70.9% female), AEs occurred in 1482 (70.8%); the most common events were lymphocyte count decreased, MS relapse, flushing, and gastrointestinal events. No cases of PML or anaphylaxis were reported; one patient developed acute kidney injury. In the effectiveness analysis ( N = 2060), least squares mean ARR decreased by 61.25% and 78.30% after 12 and 24 months' DMF treatment, respectively, versus the 12 months prior to DMF initiation (both p < 0.0001). EDSS scores remained stable over 24 months. Conclusion The safety and effectiveness of DMF in Japanese patients with MS are consistent with previous reports, with significant reductions in ARR and no new safety concerns.