What is the Optimal Timing to Assess the Effect of 5-ASA in Patients with Mild-to- Moderate Ulcerative Colitis? A Single-Center Prospective Observational Study

Background First-line therapy for mild-to-moderate ulcerative colitis is 5-aminosalicylic acid. Optimal timing for the first evaluation after initiation remains unclear. Early follow-up may not reflect efficacy, while delayed assessment could be inefficient. We conducted a prospective observational cohort study to identify the optimal evaluation time after 5-aminosalicylic acid induction in newly diagnosed patients. Methods The cohort included 157 patients at Xijing Hospital. All received standard 5-aminosalicylic acid therapy, grouped by first follow-up timing: 4 weeks (W4; N = 41), 8 weeks (W8; N = 40), or 12 weeks (W12; N = 42). Dose adjustments followed physician assessment. Primary outcome was clinical response/remission rate at Week 12 (Partial Mayo score). Secondary outcomes included inflammatory markers, mucosal healing, and dose adjustments. Results At Week 4, 68.29% of the W4 group achieved early clinical response. 82.93% in the W4 group reduced 5-aminosalicylic acid dosage by Week 4, versus 67.50% in the W8 group by Week 8. Consequently, cumulative 5-ASA exposure was lower in the W4 group. At Week 12, remission rates were similarly high across groups. At 24 weeks, long-term outcomes were comparable. Conclusion Follow-up at 4 weeks enables timely dose optimization and reduced healthcare costs without compromising 6-month efficacy. Thus, 4 weeks may be optimal for first evaluation after starting 5-ASA in mild-to-moderate ulcerative colitis. Trial Registration This trial was retrospectively registered on ClinicalTrials.gov (NCT06998693) on May 6, 2025.