Effectiveness and Tolerability of Nonmedical Switching from Originator (MabThera) to Biosimilar (Truxima) Rituximab in People with Multiple Sclerosis: A Tertiary Single-Center Observational Study

Background: Rituximab is used off-label for multiple sclerosis (MS), and biosimilar substitution raises a distinct extrapolation challenge, as MS is not an approved indication for the reference product. Real-world nonmedical switching data inform biosimilar appropriateness decisions by clinicians, societies, and payers. Objective: To report the effectiveness and tolerability of nonmedical switching from originator (MabThera) to biosimilar rituximab (Truxima) in people with MS (pwMS). Methods: A retrospective, single-center observational cohort study of 50 pwMS switched after at least two originator infusions, followed for two years. Results: Annualized relapse rate declined from 0.45 (95% CI 0.28 - 0.68) prerituximab to 0.02 (95% CI 0.00 - 0.13) on originator and 0.00 (95% CI 0.00 - 0.05) on biosimilar (p = 0.367 between products). In paired imaging analysis (n = 29), the proportion with active scans declined progressively (50.0%, 34.5%, 17.2%; Cochrans Q, p = 0.040), with no difference between the originator and biosimilar periods (McNemar, p = 0.227). B-cell depletion deepened progressively. All patients remained on biosimilar through the end of follow-up. Conclusion: Nonmedical switching from originator to biosimilar rituximab was associated with comparable clinical and radiological outcomes, supporting its use in pwMS without concern for inferior efficacy or diminished tolerability.