Mesalazine for IBS-D: The Stool-Frequency Trial

Before discussing an unfamiliar prescription for diarrhea, ask the clinician to write down the diagnosis it would treat. Bring the names and dates of tests you have already had, including any biopsy report. Ask which symptom the proposed treatment is supposed to change and how you would measure that change at follow-up.

Trial participants

Researchers randomized 136 adults with IBS-D, excluding microscopic and inflammatory colitis. They tested Pentasa granules: 2 g daily for one week, then 2 g twice daily if tolerated for 11 weeks.¹

What the stool counts showed

At weeks 11–12, mean daily stool frequency was 2.8 with mesalazine versus 2.7 with placebo. The adjusted difference was 0.1 stools/day, 95% confidence interval −0.33 to +0.53; benefit was not established.¹

Twenty withdrew; 115 provided primary diaries with at least 10/14 days completed. Available-data and missing-data imputation analyses did not establish benefit. EME funded; Ferring supplied treatment. Authors disclosed industry ties.¹²

Ask whether a quoted improvement means change from baseline or benefit over placebo.

Why the later trial matters

The postinfectious subgroup had 13 people, eight on mesalazine; post hoc findings needed confirmation.¹²

A separate 2024 study randomized 61 people with postinfectious IBS-D to long-acting Lialda 2.4 g daily or placebo for eight weeks. Analysis included 54 completers, 49 men. The primary five-item bowel symptom score favored mesalamine: standardized effect 0.57, 95% confidence interval 0.02–1.12, P=.042. This is not a percentage of patients helped. Stool frequency was a separate, nonsignificant secondary outcome. Removing constipation from the symptom score in a sensitivity analysis also produced a nonsignificant result. Shire partly funded the study and supplied tablets; authors disclosed outside commercial ties. These findings concern a selected population, formulation and outcome.³

Ask whether your symptom history matches the population being discussed, including whether symptoms followed a documented or suspected stomach infection. Bring the dates you remember, without trying to assign yourself a study subgroup.

What a prescription would be treating

The 2022 European UEG/ESNM⁴ guideline strongly recommends against mesalazine for IBS-D, rating the evidence moderate. That recommendation predates the 2024 study.⁴ A consultation can address the newer evidence and the reason a prescriber thinks it applies to your circumstances.

The current UK information for Pentasa Sachet 2g prolonged-release granules lists mild to moderate ulcerative colitis, not IBS, as its indication. IBS treatment with this product would be off-label. The information contraindicates severe kidney or liver impairment and warns of kidney injury; renal function needs regular monitoring, particularly early in treatment. NSAIDs and other medicines that can harm the kidneys may increase risk.⁵

The same information instructs immediate discontinuation for acute intolerance symptoms or signs of serious skin reactions. Ask for the prescriber’s written instructions for symptoms such as abdominal cramps with fever, severe headache, rash or mouth lesions, and how to obtain prompt advice.⁵ Do not borrow a colitis prescription or change an existing one based on an IBS trial.

For a different treatment question, see our lymphocytic-colitis trial checks.

Bloated by Dinner includes “The Visit Script”: a symptom pattern, a medicine and supplement list, dietary changes and two questions about what has been ruled out and what comes next. Use that preparation to bring the diagnostic history into the prescription discussion.