Real-World Effectiveness of and Optimization Strategies for Mirikizumab in Pediatric Ulcerative Colitis: A Prospective, Observational Study

Background Real-world evidence for mirikizumab (MIRI) in pediatric ulcerative colitis (UC) is limited. We evaluate the real-world effectiveness, remission kinetics, and optimization strategies for MIRI in pediatric UC. Methods This prospective cohort study included Japanese children with UC receiving intravenous MIRI (300 mg at weeks 0, 4, 8), followed by subcutaneous maintenance (200 mg every 4 weeks). Those without clinical remission (CR; Pediatric Ulcerative Colitis Activity Index [PUCAI] < 10 plus intestinal ultrasonographic [IUS] remission) by week 12 underwent prolonged intravenous induction every 4 weeks until week 24. Outcomes included CR, symptomatic remission (SR), ultrasonographic remission (UR), and endoscopic remission (ER). Results Twenty-eight children were included (median age 13 years; 50% female; median PUCAI 67.5; 67.4% biologics-naive). All remission measures improved by week 12 (P < 0.001). Median time to CR was 10 (interquartile range 4-16) weeks; durable CR occurred in 27/28 (96.4%). From weeks 12 to 52, CR, UR, and ER continued increasing, whereas SR plateaued. Prolonged induction delayed median CR (16 vs 8 weeks) but most patients achieved remission by week 52. On multivariate analysis, prolonged induction was the sole independent predictor of delayed CR, whereas prior biologic exposure was not. Early IUS findings differentiated patients requiring prolonged induction or with prior biologic exposure. No serious adverse events occurred, and MIRI was well tolerated. Conclusions MIRI can induce and sustain CR in pediatric UC, particularly when early optimization strategies are applied. These findings highlight IUS as a useful surrogate for mucosal healing and support MIRI as a promising, adaptable, and safe therapeutic option in pediatric UC.