INTRODUCTION: Abdominal pain is the principal symptom of irritable bowel syndrome (IBS). This analysis examined abdominal pain response in adults with IBS with diarrhea (IBS-D) receiving the nonsystemic antibiotic rifaximin. METHODS: In the Targeted Nonsystemic Antibiotic Rifaximin Gut-Selective Evaluation of Treatment for IBS-D 3 trial, adults with IBS-D received open-label rifaximin 550 mg 3 times daily for 2 weeks, followed by the 4-week post-treatment phase assessing abdominal pain and stool consistency response. Responders were followed for up to 18 additional weeks; patients with recurrence were randomly assigned to receive two 2-week courses of double-blind rifaximin 550 mg 3 times daily or placebo, separated by 10 weeks. Analyses evaluated mean weekly improvements from baseline (e.g., ≥30%, ≥40%, and ≥50%) in abdominal pain during the 4-week post-repeat-treatment phases. RESULTS: Of the 2,438 evaluable patients, 1,384 (56.8%) had abdominal pain response to open-label rifaximin (≥30% improvement from baseline in the mean weekly abdominal pain score during ≥2 of the first 4 weeks post-treatment). Weekly decrease (improvement) in responders' mean abdominal pain score (scale range, 0-10) from baseline ranged from -2.6 to -3.3 points during the 18-week follow-up. After the first double-blind repeat treatment, a significantly higher percentage of rifaximin-treated patients were abdominal pain responders (53.9% [172/319]) vs placebo (44.4% [134/302], P = 0.02), with similar results after the second repeat treatment (52.9% [155/293] vs 44.7% [123/275], respectively, P = 0.047). A significantly higher percentage of rifaximin-treated patients were weekly abdominal pain responders for ≥50% of the 18-week double-blind repeat treatment phase (47.9% [138/288] vs 35.9% [97/270], P = 0.004). DISCUSSION: Rifaximin is efficacious in improving abdominal pain in adults with IBS-D.
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