Characterization of Abdominal Pain Response to Rifaximin in Patients with Irritable Bowel Syndrome with Diarrhea (IBS-D), by Baseline Pain Severity: Presidential Poster Award

Abstract

Introduction: Rifaximin is indicated for the treatment of IBS-D in adults. This post hoc analysis of a phase 3 trial evaluated response to 2 courses of rifaximin in patients subgrouped by baseline abdominal pain severity. Methods: Adults with IBS-D (mean daily abdominal pain score ≥3) received a 2-week course of rifaximin 550 mg three times daily. Abdominal pain was assessed daily (score range, 0-10). Patients who responded (during 4-week evaluation period) and then had symptom recurrence during an additional ≤ 18-week observation period (up to 22 weeks post-treatment) received a second 2-week rifaximin course and response was assessed during a 4-week evaluation period. Response was defined as a ≥30% decrease from baseline in mean weekly abdominal pain score and ≥50% decrease from baseline in days/week with Bristol Stool Scale type 6/7 (mushy/watery) stool (composite endpoint) for ≥2 of the first 4 weeks post-treatment. Subgroups were defined by baseline abdominal pain scores of <5.0 (group A), ≥5.0 to <8.0 (group B), and ≥8.0 (group C). Results: 2579 patients received the first rifaximin course (68.2% female; mean age, 46.4 y; mean baseline abdominal pain score, 5.5 [median, 5.4]). In 2438 patients evaluable for efficacy (group A, n=962; group B, n=1260; group C, n=216), response to rifaximin (composite endpoint) was observed in 40.4%, 47.0%, and 43.1% of patients in groups A, B, and C, respectively. Response for the individual abdominal pain component was observed in 57.0%, 57.9%, and 49.5% of patients, respectively. In 328 patients who experienced symptom recurrence and received repeat treatment with rifaximin (group A, n=114; group B, n=178; group C, n=36), median baseline abdominal pain score at repeat treatment baseline was 4.4 (mean, 4.6), lower than observed at first-course baseline. When subgrouped by repeat treatment baseline pain score, response to repeat rifaximin treatment (composite endpoint) was reported in 38.6%, 34.8%, and 27.8% of patients in groups A, B, and C, respectively. Response for abdominal pain component was reported by 57.9%, 50.6%, and 50.0% of patients, respectively. Conclusion: In adults with IBS-D treated with rifaximin, a high percentage of patients had clinically meaningful improvement in abdominal pain irrespective of baseline abdominal pain severity category and treatment course (first vs repeat treatment). These data support rifaximin efficacy in improving IBS-related abdominal pain symptoms.