Safety and Effectiveness of Inebilizumab in Patients with Neuromyelitis Optica Spectrum Disorder: Interim Analysis of a Post-marketing Surveillance in Japan

INTRODUCTION: Inebilizumab is used in Japan for relapse prevention in aquaporin-4 (AQP4) antibody-positive neuromyelitis optica spectrum disorder (NMOSD). Nationwide post-marketing surveillance (PMS) is underway to evaluate the real-world safety and effectiveness of inebilizumab in Japanese patients with NMOSD. METHODS: This PMS interim analysis assessed safety and effectiveness of inebilizumab in Japanese patients with NMOSD initiating treatment between June 2021 and November 2023, using data through June 2025. RESULTS: The safety analysis set included 228 patients, and the effectiveness analysis set included 224 patients after excluding three patients from N-MOmentum (NCT02200770) and one without confirmed anti-AQP4 antibody positivity. Twenty-one (safety analysis set) and 20 (effectiveness analysis set) patients discontinued treatment. In the safety analysis set, 194 patients (85.1%) were female, and the mean ± standard deviation (SD) age was 54.2 ± 13.1 years. Adverse drug reactions (ADRs) occurred in 74 patients (32.5%); 31 (13.6%) were serious. Common ADRs were infections (14.5%, n = 33); serious infections (5.7%, n = 13) included COVID-19 (1.3%, n = 3), COVID-19 pneumonia (0.9%, n = 2), and urinary tract infection (0.9%, n = 2). Two fatal ADRs (interstitial lung disease, sudden cardiac death) occurred, for which a causal relationship with inebilizumab could not be excluded. In the effectiveness analysis set, the annualized relapse rate (95% CI) decreased from 0.40 (0.33-0.47) per person-year during the 2 years before inebilizumab initiation to 0.10 (0.07-0.14) per person-year after inebilizumab initiation. From baseline to 1 year, the proportion of patients receiving neither concomitant oral glucocorticoids nor immunosuppressants increased from 5.4% to 33.0%, and the mean ± SD oral glucocorticoid dose decreased from 11.7 ± 7.9 mg/day to 4.3 ± 4.7 mg/day. CONCLUSION: In this interim analysis, the safety profile of inebilizumab was consistent with prior evidence and no new safety concerns were identified. Inebilizumab reduced relapse rates and decreased concomitant use of oral glucocorticoids and immunosuppressants in patients with NMOSD. UMIN CLINICAL TRIALS REGISTRY: UMIN000044431.