Objectives: Irritable bowel syndrome (IBS) affects 10-15% of the population, and treatment options are limited. Rifaximin is a minimally absorbed antibiotic that has shown efficacy in IBS patients. The objective of our study was to perform a meta-analysis and systematic review of available randomized, placebo controlled trials evaluating the efficacy and tolerability of rifaximin in patients with IBS.
Methods: We performed a systematic literature search of multiple online electronic databases regardless of language. Inclusion criteria entailed randomized, placebo controlled trials and IBS defined by accepted symptom-based criteria. Meta-analysis was conducted to evaluate the summary odds ratios (ORs) and 95% confidence intervals (CIs) of combined studies for the primary and secondary outcomes using a random-effects model based on the DerSimonian and Laird method to reflect both within- and between study variability. We assessed heterogeneity using χ(2) test and the inconsistency index statistic (I(2)). Significant heterogeneity was defined as I(2) ≥25%. Meta-regression was performed using generalized linear mixed-effects model and study as random effects to estimate the summary OR adjusting for covariate differences across studies and treatment group. Publication bias was assessed by funnel plot analysis.
Results: Systematic review identified 13,700 citations. Eighteen were deemed to be potentially relevant, of which five articles met eligibility. Meta-analysis found rifaximin to be more efficacious than placebo for global IBS symptom improvement (OR=1.57; 95% CI=1.22, 2.01; therapeutic gain=9.8%; number needed to treat (NNT)=10.2), with mild heterogeneity (P=0.25, I(2)=26%). For the key secondary outcome of bloating, raw data were available for four studies. Rifaximin was significantly more likely to improve bloating than placebo (OR=1.55; 95% CI=1.23-1.96; therapeutic gain=9.9%; NNT=10.1), with no significant heterogeneity (P=0.27, I(2)=23%). We found that studies with older patients and more females demonstrated higher response rates, which was consistent regardless of treatment group. In addition, studies with higher cumulative dose tended to report a higher response rate. Of the covariates evaluated, we found age to be most predictive of response, with a correlation coefficient of 0.97 between aggregate response rate and mean age in the placebo groups. Although studies with higher cumulative dose tended to show increased response rates, this was also seen consistently in both the treated and placebo groups. Adverse effects were similar among patients receiving rifaximin or placebo in all studies. The most common adverse events (AEs) (≤10%) with rifaximin were headache, upper respiratory infection, nausea, nasopharygitis, diarrhea, and abdominal pain. Serious AEs were rare (<1%) and similar with rifaximin and placebo.
Conclusions: Rifaximin proved more effective than placebo for global symptoms and bloating in IBS patients. The modest therapeutic gain was similar to that yielded by other currently available therapies for IBS. AEs were similar between rifaximin and placebo.