Long-Term Safety of Ontamalimab in Patients with Moderate to Severe Inflammatory Bowel Disease

Purpose: Although ontamalimab showed promise for treatment of patients with ulcerative colitis (UC) and Crohn’s disease (CD), the Phase 3 clinical development program was terminated in 2020. Here we report the results of a long-term safety (LTS) extension study. Patients and Methods: The study enrolled patients with UC or CD who previously participated in the randomized, placebo-controlled phase 3 induction and maintenance clinical trials that evaluated the efficacy and safety of ontamalimab. During the LTS study, patients received ontamalimab 25 mg or 75 mg once every 4 weeks or were switched from 25 mg to 75 mg. Long-term safety outcomes, including the frequency and severity of adverse events (AEs), were assessed in eligible patients for up to 6 years of treatment. Efficacy was not formally evaluated in this study. Results: Long-term safety was evaluated in 516 patients with UC and 41 patients with CD. Across all ontamalimab dose groups in UC, 392 patients (76.0%) had AEs; 115 serious AEs occurred in 82 patients (15.9%) and 2 AEs led to patient deaths during the study. Across all ontamalimab dose groups in CD, 29 patients (70.7%) had AEs; 10 serious AEs occurred in 8 patients (19.5%) and 1 AE led to a patient death during the study. Deaths were not related to receiving ontamalimab. In patients with UC and CD, 245/253 and 18/19 who completed the study, respectively, had a treatment response at the study end. Conclusion: Ontamalimab was well tolerated and had an acceptable long-term safety profile in patients with UC and CD. Keywords: Crohn’s disease, long-term safety, mucosal addressin cell adhesion molecule-1, ontamalimab, ulcerative colitis