A Pilot Study of the Effectiveness of a Short Course of Rifaximin 2200 mg/day on Abdominal Symptoms and its Effects on Quality of Life in Patients with Moderate to Severe Diarrhea-Predominant Irritable Bowel Syndrome.

Background and objective: Rifaximin is used to treat diarrhea-predominant irritable bowel syndrome (IBS-D). However, determining the most effective regimen remains a challenge. This study aimed to evaluate the effectiveness and safety of a 10-day high-dose course of rifaximin (2200 mg/day) and its effects on both abdominal symptoms and quality of life (QOL) in patients with IBS-D.

Method: Adult patients with moderate to severe IBS-D (Rome IV) and fecal urgency and bloating were prescribed rifaximin 1100 mg twice daily for 10 days. Demographic information, the IBS Symptom Severity Index (IBS-SSI) score (using a 7-point Likert scale), and Bristol Stool Scale (BSS) score were recorded at baseline, day 10, and 4 weeks after treatment cessation. IBS Symptom Severity Score (IBS-SSS) and IBS-QOL scores were recorded at baseline and day 10. Any drug adverse effects were recorded.

Results: In total, 39 patients completed the study. Average scores for all abdominal symptoms and BSS showed significant improvement at day 10 and 4 weeks after treatment cessation (all p < 0.001). A significant improvement was seen in IBS-SSS and overall IBS-QOL score at day 10 (p < 0.001), with the highest improvement (31%) in interference with activity. Moreover, composite improvement rates were 38.64% for all abdominal symptoms, together with BSS < 5, bi-composite (66.67% for abdominal pain + bloating; 61.54% for abdominal pain + urgency), and 56.41% for tri-composite (abdominal pain + bloating + urgency) symptoms. Notably, no serious adverse effects were reported, and the adherence rate was 94.9%.

Conclusions: Abdominal symptoms and overall QOL, especially in social and work dimensions, significantly improved in patients with moderate to severe IBS-D following a regimen of rifaximin 2200 mg/day, which was well tolerated.