Background  The 5‐HT₃ receptor antagonists are known to be effective for the treatment of diarrhea‐predominant irritable bowel syndrome (IBS), but not widely used yet. The aim of this study was to compare the efficacy and safety of ramosetron, a 5‐HT₃ receptor antagonist, and mebeverine in male patients with IBS with diarrhea (IBS‐D).

Methods  This study was performed in a multicenter, randomized, open‐label design. Data of 343 male patients with IBS‐D who were randomized to either a 4‐week treatment of ramosetron 5 μg once daily or a 4‐week treatment of mebeverine 135 mg three times daily were analyzed by the intent‐to‐treat analysis. The primary efficacy parameter was the proportion of patients with adequate relief of IBS symptoms at the last week of treatment. The secondary endpoints were changes in each symptom score and the safety profiles.

Key Results  The responder rates for global IBS symptoms, abdominal pain/discomfort and abnormal bowel habits in the ramosetron and mebeverine groups significantly increased during the treatment period. The severity scores of abdominal pain/discomfort and urgency, the stool form score, and the stool frequency in both treatment arms were significantly reduced, compared with the baselines. There were no significant differences in the responder rates (37%vs 38% on ITT analysis) and adverse event profiles between the ramosetron and mebeverine groups. Neither severe constipation nor ischemic colitis was reported by ramosetron‐treated patients.

Conclusions & Inferences  Ramosetron 5 μg once daily is as effective as mebeverine three times daily in male patients with IBS‐D.