Real-World Effectiveness and Safety of Ofatumumab in Relapsing Multiple Sclerosis: Comparison of Treatment-Naïve Patients and Switchers in a Multicenter Cohort

Background: Ofatumumab (OFA) is a fully human anti-CD20 monoclonal antibody approved for the treatment of relapsing multiple sclerosis (RMS). Real-world data on its effectiveness and safety remain limited. Objective: To assess the effectiveness and safety of OFA in a large Italian RMS cohort and to examine the impact of prior treatment exposure on clinical, radiological, and safety outcomes in routine clinical practice. Methods: This retrospective, multicenter study included adults with RMS who initiated OFA and had at least one follow-up visit. Patients were classified as treatment-naïve, switching from moderate-efficacy therapies (MET), or switching from high-efficacy therapies (HET). Outcomes included annualized relapse rate (ARR), magnetic resonance imaging (MRI) activity, disability measures (including confirmed disability worsening and improvement), no evidence of disease activity (NEDA-3), and adverse events (AEs). Results: A total of 424 patients were analyzed, with a mean follow-up of 1.32 (± 0.61) years: 101 (23.8%) treatment-naïve and 323 (76.2%) switchers, of whom 113 were previously treated with MET and 210 with HET. During treatment, ARR decreased significantly from 0.486 to 0.027 (94.5% reduction; p < 0.001), with comparable relative reduction observed across all subgroups. MRI activity was significantly diminished, and at 12 months, 79.3% of evaluable patients achieved NEDA-3, with no significant differences between naïve, MET, and HET subgroups. Overall, OFA was well tolerated, with predominantly mild injection-related reactions and low discontinuation rates, mainly related to pregnancy planning with favorable outcomes. Infections were the only safety outcome that differed significantly among groups, occurring in 0.9% of naïve patients, 1.7% of MET switchers, and 9.5% of HET switchers (p = 0.001). Prior exposure to HET was the only independent predictor of infections. Conclusions: These findings support OFA as an effective and generally safe option for RMS across various treatment sequences, while suggesting enhanced infection monitoring in patients switching from HETs.