The Efficacy of Probiotics in the Therapy of Irritable Bowel Syndrome (IBS)

Abstract

Purpose: IBS is common and can be difficult to treat. Bacteria may be important in the pathogenesis of IBS and altering the microbial environment with probiotics may be an effective therapy. Randomized controlled trials (RCTs) have been conflicting so we conducted a systematic review for the updated ACG monograph on IBS. Methods: Medline (1966–2007), Embase (1988–2007) and the Cochrane Controlled Trials Register (2007) electronic databases were searched as were abstracts from DDW and UEGW and contacted authors for extra information. We included only parallel group RCTs with at least one week of therapy comparing probiotics with placebo or no treatment in adults with IBS according to any acceptable definition. Studies had to provide abdominal pain or global IBS symptom improvement as an outcome. Eligibility assessment and data extraction were performed by two independent researchers. Data was synthesized using relative risk (RR) of symptoms not improving for dichotomous data and standardized mean difference (SMD) for continuous data using random effects models. Results: We identified 19 RCTs (18 papers) in 1628 IBS patients. The quality of the trials was reasonable with 8 reporting adequate methods of randomization and 5 reporting method of concealment of allocation. Fifteen RCTs were double blind. There were 9 RCTs involving 836 patients that gave outcomes as a dichotomous variable. Probiotics were statistically significantly better than placebo (RR of IBS not improving = 0.67; 95% CI = 0.49 to 0.91) with an NNT = 4 (95% CI = 2 to 20) and significant heterogeneity (I2 = 75%, Cochran Q = 32.2, df = 8, P < 0.0001). There were 15 trials assessing 1351 patients that reported improvement in IBS score as a continuous outcome. There was a statistically significant effect of probiotics in reducing symptom score (SMD = −0.35; 95% CI = −0.62 to −0.09) with significant heterogeneity (I2 = 79%, Cochran Q = 67.8 df = 14 P < 0.0001). Four trials evaluated lactobacillus alone and there was no statistically significant benefit over placebo. There were 9 trials using combinations of probiotics (all but one including bifidobacterium) that did suggest a significant improvement in IBS symptoms score with active treatment (SMD –0.5; 95% CI = −0.91 to −0.09). There was evidence of funnel plot asymmetry (Egger test = −2.92; 95% CI = −5.10 to −0.74, P= 0.017) for the continuous data but not the dichotomous data. Conclusion: Probiotics may be efficacious in IBS particularly when used in combinations that contain bifidobacterium. There is evidence of publication bias or other small study effects however and it is therefore possible that the efficacy of probiotics has been overestimated.