Comaprison of Efficacy and Safety Between Etrasimod vs Mesalazine in Chinese Adults With Active UC

Ulcerative colitis (UC) is a chronic, relapsing inflammatory disease of the colon that causes diarrhea, bleeding, and abdominal pain. Mesalazine (5-aminosalicylic acid) is the current standard first-line treatment for mild-to-moderate UC, but many patients do not respond well enough, and some experience side effects. Etrasimod is an oral, selective sphingosine-1-phosphate (S1P) receptor modulator that helps reduce gut inflammation by keeping immune cells from moving into the intestinal wall. This study will test whether etrasimod works better than mesalazine in Chinese adults with active UC. The study plans to enroll about 320 patients from multiple hospitals across China. Eligible participants are adults aged 18 years or older with active UC, defined by a modified Mayo score of 3 to 6 (including specific endoscopic and bleeding criteria). Both newly diagnosed patients (within the past 4 weeks, with no prior UC treatment) and those who had an inadequate response, intolerance, or non-standard use of conventional therapies-but who have never taken biologics or other small-molecule drugs-may join. Patients will be randomly assigned in a 1:1 ratio to receive either etrasimod 2 mg once daily or mesalazine (starting at 4 g/day for 12 weeks, then at least 2 g/day based on response) for 24 weeks. Randomisation will balance important factors like steroid use and baseline endoscopic severity. The primary research objective is whether more patients on etrasimod achieve clinical remission at week 24. Clinical remission means no rectal bleeding, normal or near-normal stool frequency, and an endoscopic score of 1 or less (without easy bleeding). The study will also measure other benefits, such as symptom improvement, endoscopic healing, normalisation of blood and stool inflammation markers, bowel ultrasound response, tissue healing, and quality of life using standard questionnaires. Safety will be carefully tracked by recording all adverse events during treatment and follow-up.