Objectives: Irritable bowel syndrome (IBS) is a common disorder and available therapies have limited efficacy. Mucosal inflammation and alterations in gut microflora may contribute to the development of IBS symptoms, and researchers have hypothesized that probiotics might improve these symptoms. The aim of this study was to perform a systematic review of randomized controlled trials (RCTs) evaluating the efficacy, safety, and tolerability of probiotics in the treatment of IBS. Methods: Comprehensive literature searches of multiple databases were performed. Study selection criteria were as follows: (i) RCTs, (ii) adults with IBS defined by Manning or Rome II criteria, (iii) single or combination probiotic vs. placebo, and (iv) improvement in IBS symptoms and/or decrease in frequency of adverse events reported. Data about study design and results were extracted in duplicate using standardized data extraction forms. Owing to variability in outcome measures, quantitative pooling of data was not feasible. Results: A total of 16 RCTs met selection criteria. Of those, 11 studies showed suboptimal study design with inadequate blinding, inadequate trial length, inadequate sample size, and/or lack of intention-to-treat analysis. None of the studies provided quantifiable data about both tolerability and adverse events. Bifidobacterium infantis 35624 showed significant improvement in the composite score for abdominal pain/discomfort, bloating/distention, and/or bowel movement difficulty compared with placebo (P<0.05) in two appropriately designed studies. No other probiotic showed significant improvement in IBS symptoms in an appropriately designed study. Conclusions: B. infantis 35624 has shown efficacy for improvement of IBS symptoms. Most RCTs about the utility of probiotics in IBS have not used an appropriate study design and do not adequately report adverse events. Therefore, there is inadequate data to comment on the efficacy of other probiotics. Future probiotic studies should follow Rome II recommendations for appropriate design of an RCT.
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