Background: Mirikizumab, an anti-p19IL-23 monoclonal antibody, has shown efficacy and safety in treating moderately to severely active ulcerative colitis (UC) in clinical trials. We assessed the effectiveness and safety of mirikizumab for the treatment of UC in a real-world setting.

Methods: We conducted a prospective observational study of adult patients with UC who were started on mirikizumab for active disease between January 1, 2024, and April 30, 2024. Clinical, biochemical, sonographic, and endoscopic data were collected. The primary outcome was clinical response and remission at 12 weeks, and secondary outcomes included corticosteroid-free remission (CSFR) and biochemical marker improvement at week 12. Adverse events were recorded.

Results: Twenty-two patients were initiated on mirikizumab during the study period, with 20 included in the analysis. The majority were female (65%) and had a median duration of disease of 12 years (IQR 8.0-18.5]. The majority of patients had previously been exposed to three or more advanced therapies (70% of patients) prior to mirikizumab start. Clinical remission (SCCAI < 3) increased from 30% at baseline to 83% at week 12. CSFR increased from 15% at baseline to 78% at week 12. Median SCCAI scores significantly decreased from 3.5 at baseline to 0.5 at week 12 (p < 0.001), driven primarily by an improvement in general well-being and a decrease in urgency. Adverse effects were mild to moderate, with one serious event of streptococcal pharyngitis.

Conclusions: Mirikizumab demonstrated significant clinical effectiveness in achieving clinical remission, response, and CSFR in patients with UC.