Introduction

Mesalazine remains a first-line therapy for mild-to-moderate ulcerative colitis (UC), but optimal dosing, combined oral–rectal treatment, and formulation selection remain uncertain.

Aim

To evaluate outcomes after mesalazine optimisation and compare oral doses within left-sided colitis (E2) and extensive colitis (E3) as well as oral formulations.

Material and methods

UC-INCREASE retrospectively included 243 adults: 152 with E2 receiving oral mesalazine plus a rectal enema and 91 with E3 receiving oral mesalazine alone. Oral doses of 3 versus 4 g/day were compared within E2 and E3; prolonged-release granules were compared with other tablets. Endpoints included component-verified clinical remission based on Partial Mayo Score (PMS) ≤ 2 or Total Mayo Score (TMS) ≤ 2, endoscopic Mayo subscore (eMayo) = 0, and faecal calprotectin (FC) < 250 µg/g. Comparisons used unadjusted odds ratios (ORs).

Results

Median C-reactive protein decreased from 16.8 to 4.5 mg/l, FC from 516 to 111 µg/g, TMS from 6 to 2, and PMS from 5 to 1 (all p < 0.001). PMS-defined, TMS-defined, endoscopic, and biochemical remission occurred in 86%, 57%, 24%, and 81%, respectively. Within E2, endoscopic remission was more frequent with 4 versus 3 g/day plus rectal mesalazine (45% vs. 8%; OR = 8.89, 95% CI: 3.26–24.25; p < 0.001). Within E3, no endpoint differed significantly between doses. Prolonged-release granules were associated with improvement of all endpoints and fewer recorded adverse events (26% vs. 62%; OR = 0.21).

Conclusions

Mesalazine optimisation was associated with broad improvement. Comparative findings were exploratory and require prospective confirmation.