Planned dose reduction of ocrelizumab in relapsing-remitting multiple sclerosis: a single-centre observational study.

Background: Ocrelizumab, a humanised anti-CD20 monoclonal, is a highly effective treatment for relapsing-remitting multiple sclerosis (RRMS). The long-term safety of B-cell depletion in RRMS, however, is uncertain and there are no data on dose reduction of ocrelizumab as a risk mitigation strategy. This study aimed to evaluate the effectiveness and safety of reducing ocrelizumab dose from 600 to 300 mg in patients with RRMS.

Method: Data were collected through the Townsville neurology service. Following the standard randomised controlled trial regimen of 600 mg every 6 months for 2 years, sequential patients consented to dose reduction to 300 mg every 6 months. Patients were included if they were diagnosed with RRMS and received at least one reduced dose of ocrelizumab. Relapse, disability progression, new MRI lesions, CD19⁺ cell counts and immunoglobulin concentrations were analysed.

Results: A total of 35 patients, treated with 177 full and 107 reduced doses, were included. The mean follow-up on reduced dose was 17 (1-31) months. We observed no relapses or new MRI activity in the cohort receiving the reduced dose, accompanied by persistent CD19+B cell depletion (≤0.05×10⁹/L). Mean IgG, IgA and IgM levels remained stable throughout the study. No new safety concerns arose.

Conclusions: In this single-centre observational study, dose reduction of ocrelizumab from 600 to 300 mg every 6 months after 2 years appeared to maintain efficacy in terms of new inflammatory disease activity. A randomised trial may be warranted to confirm this and explore the impact of dose reduction on long-term safety.