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

Efficacy and Safety of Etrasimod Versus Mesalazine in Chinese Adult Patients With Active Ulcerative Colitis: A Multicenter, Randomized, Open-Label, Superiority Trial

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.

This is an open-label study (patients and clinical staff know which drug is given) to reflect real-world practice, but the clinical staff who read the colonoscopy results and tissue samples will not know the treatment assignment. An independent statistician will analyse the results. One interim analysis is planned to check for early evidence of benefit or futility. The study involves 24 weeks of treatment, with visits at baseline, week 6, week 12, and week 24, plus a 4-week safety follow-up.

Sample size calculation indicates that 320 participants (160 per group) will provide 90% power to detect a clinically important difference, accounting for a 30% dropout rate. The primary analysis will compare remission rates between groups, adjusting for the stratification factors. All findings will be published to share knowledge with the medical community and help guide future treatment decisions for UC patients in China.

Inclusion Criteria:

• Male or female, aged 18 years or above.
• Patients diagnosed with active ulcerative colitis at multiple centers including Sir Run Run Shaw Hospital, Zhejiang University School of Medicine (lead center), defined as having a modified Mayo Score (without physician's global assessment) ranging from 3 to 6 points. If ES = 1 point, RBS ≥ 1 point is required. Patients with proctitis are allowed to be enrolled, provided that the proctitis lesion extends more than 5 cm from the anal verge.
• Treatment-naive patients at initial visit accounting for no more than 30% of the total sample size; Or patients who have previously received conventional pharmacological therapy (including mesalazine, corticosteroids and immunosuppressants) but have inadequate response, intolerance (excluding mesalazine), or non-standard treatment (including but not limited to insufficient dosage or duration of oral 5-ASA, corticosteroids or immunosuppressants, which shall be determined by the investigator based on individual patient conditions). The proportion of patients receiving combined glucocorticoid therapy at baseline shall not exceed 30% of the total sample size.
• Voluntarily participate in this study and sign the informed consent form.

Exclusion Criteria:

• Subjects with contraindications to etrolimod or mesalazine.
• Previously treated with etrasimod or other biologics and small-molecule drugs.
• Patients are currently receiving full-dose conventional therapy yet still have active disease, including any one of the following:

Treatment with mesalazine (≥3 g/day) for ≥8 weeks; Or continuous treatment with prednisone ≥40 mg/day or equivalent dose for ≥3 days (intravenous administration); Or continuous oral treatment with prednisone >20 mg/day or equivalent dose for ≥2 weeks; or oral azathioprine (≥0.75 mg/kg/day), 6-mercaptopurine (≥0.5 mg/kg/day), methotrexate (≥15 mg/week) for ≥3 months.

• Recent history of acute severe ulcerative colitis (ASUC), toxic megacolon, etc.
• Patients with stomas or patients with UC scheduled for inpatient surgical intervention.
• Pregnant and lactating women.
• Vulnerable groups excluding the elderly and illiterate, including people with mental illnesses, individuals with cognitive impairment, critically ill patients, etc.
• Other circumstances where researchers consider participation in this study inappropriate.