Clinical Characteristics and Outcomes of Rome IV Diarrhea‐Predominant Irritable Bowel Syndrome and Functional Diarrhea Prescribed With Ondansetron: A Real‐World Study

Background 5‐HT3 receptor antagonists, such as ondansetron, are effective in the management of irritable bowel syndrome‐diarrhea predominant (IBS‐D). However, real‐world data and evidence exploring the response to ondansetron in patients with functional diarrhea (FDr) are lacking. The aim of this study was to assess the clinical characteristics and response to ondansetron among patients with bowel disorders associated with chronic diarrhea in a real‐world setting. Methodology We conducted a retrospective study of consecutive patients (October 2016–February 2024) diagnosed with IBS‐D or FDr in a tertiary care neurogastroenterology outpatient clinic. Demographic, clinical data, previous surgery, relevant investigations and current medications were collected. Clinical response to ondansetron was defined as (i) a reduction of at least one bowel movement/day versus baseline and (ii) firmer stool consistency (an improvement of ≥ 1 on the Bristol Stool Form Scale [BSFS] vs. baseline). Results Ninety‐two patients were included, among whom 75 (81%) and 17 (18%) had IBS‐D and FDr, respectively. Urgency to defecate was significantly more frequent in patients with FDr versus IBS‐D ( p = 0.003). Sixty‐eight of the 92 patients (73.9%) reported a clinical response to ondansetron, which was maintained at a median dosage of 8 mg/day for a median duration of 19 months with few minor side effects. Conclusion When used in clinical practice, 8 mg/day of ondansetron is associated with a reduction in bowel frequency and an improvement in fecal consistency in approximately two‐thirds of patients with IBS‐D and FDr.