Efficacy and safety of mirikizumab in maintenance therapy for ulcerative colitis in difficult-to-treat inflammatory bowel disease: a single-center retrospective study in Japan

Background/Aims: Randomized controlled trials have confirmed the efficacy and safety of mirikizumab, an anti-interleukin-23p19 monoclonal antibody, for moderate-to-severe active ulcerative colitis (UC). However, there are no real-world data on the efficacy and safety of mirikizumab for UC as maintenance therapy, especially in difficult-to-treat inflammatory bowel disease (DTT-IBD). This study aimed to evaluate the long-term efficacy and safety of mirikizumab in patients with UC of DTT-IBD. Methods: This was a single-center retrospective observational study involving adult patients with UC who received mirikizumab between January 2023 and April 2025 and met the criteria for DTT-IBD (e.g., failure of biologics and advanced small molecule drugs with at least 2 different mechanisms of action). The primary outcome was the clinical response at week 52. Secondary outcomes included steroid-free clinical remission within 52 weeks and the persistency of mirikizumab use. Adverse events were also recorded. Results: Thirty-two patients were included in this study. The median 2-item patient-reported outcome score at baseline was 3 (interquartile range, 2-4). The proportion of patients with a clinical response at week 52 was 33.3% (95% confidence interval, 14.6%-57.0%). Steroid-free clinical remission was achieved in 26.7% (95% confidence interval, 12.3%-45.9%) of the patients. The cumulative continuous rate of mirikizumab use at week 52 was approximately 60%. Only 1 patient developed a serious adverse event requiring hospitalization (pneumonia), and mirikizumab was successfully resumed after recovery. Conclusions: The present study demonstrated real-world data regarding maintenance therapy with mirikizumab for UC among patients with DTT-IBD.