Ondansetron shows potential in irritable bowel syndrome with diarrhoea

A study on titrated ondansetron for the treatment of irritable bowel syndrome with diarrhoea (IBS-D) has fallen short of meeting the endpoint due to being underpowered. However, when data from this study and two others were pooled in a meta-analysis, ondansetron appears to yield significant improvements in the composite endpoint set by the Food and Drug Administration (FDA), namely stool consistency and urgency. 

The current study included 80 patients with IBS-D who were randomly assigned to treatment with either ondansetron 4 mg once daily (titrated up to 8 mg three times a day) or placebo. The primary endpoint was the percentage of responders using the FDA composite endpoint. Secondary and mechanistic endpoints were stool consistency (Bristol Stool Form Scale) and whole gut transit time (WGTT).

Intention-to-treat analysis showed no significant difference in the number of patients who met the primary endpoint in the ondansetron and placebo arms (15 out of 37; 40.5 percent, 95 percent confidence interval [CI], 24.7–56.4 vs 12 out of 43; 27.9 percent, 95 percent CI, 14.5–41.3; p=0.19).

Meanwhile, results for stool consistency favoured ondansetron over placebo (adjusted mean difference, −0.7, 95 percent CI, −1.0 to −0.3; p<0.001). Furthermore, ondansetron produced greater improvements in WGTT between baseline and week 12 (mean difference, 3.8 vs −2.2 hours; p=0.01).

Then, researchers conducted a literature review and identified two trials similar to the current study. A total of 327 patients were included in the meta-analysis.

Pooled data showed that ondansetron was superior to placebo for the FDA composite endpoint (relative risk [RR], 0.86, 95 percent CI, 0.75–0.98; number needed to treat [NNT]=9) and stool response (RR, 0.65, 95 percent CI, 0.52–0.82; NNT=5), but not abdominal pain response (RR, 0.95, 95 percent CI, 0.74–1.20).