Rifaximin Treatment for Individual and Multiple Symptoms of Irritable Bowel Syndrome With Diarrhea: An Analysis Using New End Points

Purpose: Rifaximin is indicated for the treatment of irritable bowel syndrome with diarrhea (IBS-D) in adults. The current aim was to evaluate rifaximin efficacy on individual and composite IBS-D symptoms using definitions not previously examined. Methods: Phase III post hoc analyses of two randomized, double-blind, placebo-controlled trials and the open-label phase of a randomized, double-blind, placebo-controlled trial were conducted. Adults with IBS-D received a 2-week course of rifaximin 550 mg TID. Individual and composite responses for abdominal pain (mean weekly improvements from baseline of ≥30%, ≥40%, or ≥50%), bloating (mean weekly improvements from baseline of ≥1 or ≥2 points; or ≥30%, ≥40%, or ≥50%), stool consistency (mean weekly average stool consistency score <3 or <4), and urgency (improvement from baseline of ≥30% or ≥40% in percentage of days with urgency) for ≥2 of the first 4 weeks after treatment, and weekly for 12 weeks, were assessed. Findings: Overall, 1258 patients from the double-blind trials (rifaximin [n = 624]; placebo [n = 634]) and 2438 from an open-label trial were analyzed. The percentage of bloating or urgency responders was significantly greater with double-blind rifaximin versus placebo (P ≤ 0.03). A significantly greater percentage of the double-blind group were composite abdominal pain and bloating responders versus placebo for all thresholds analyzed (P < 0.05). A significantly greater percentage of the double-blind group were tri-symptom composite end point responders (abdominal pain, bloating, and fecal urgency) versus placebo (P = 0.001). A significantly greater percentage of patients achieved response (≥30% composite tri-symptom threshold) with double-blind rifaximin versus placebo as early as 1 week posttreatment, with significance maintained through ≥5 weeks after treatment. Open-label results were consistent with those of the double-blind study. Implications: Rifaximin significantly improved multiple, concurrent IBS-D symptoms, using clinically relevant definitions of treatment response. Using a novel tri-symptom composite end point (ie, abdominal pain, bloating, fecal urgency), adults with IBS-D treated with a 2-week course of rifaximin were significantly more likely to be composite end point responders than those receiving placebo (≥30% or ≥40% threshold) for the three symptoms. Thus, rifaximin not only met current standard thresholds used for adjudication of responders in clinical trials but also achieved higher thresholds for many of these symptoms, suggesting potential for even more robust clinical improvements. ClinicalTrials.gov identifiers: NCT00731679, NCT00724126, and NCT01543178.