The group receiving S. boulardii (SRAC) had a 75% eradication rate in both ITT and PP analyses, the group receiving triple therapy (RAC) had a 62.5% (ITT) and 65.2% (PP) eradication rate, and the group receiving quadruple therapy (BRAC) had an 85.42% (ITT) and 93.18% (PP) rate. As expected, the BRAC group was found to have a marginally higher efficacy than either of the groups receiving triple therapy.
However, the SRAC group had a significantly lower incidence of adverse events than the other two groups, as well as a greater reduction in dyspepsia by the end of the trial. For example, no participants receiving SRAC experienced abdominal pain, and only 1 (2%) experienced diarrhea, in contrast to a 4-6% incidence of abdominal pain and 9-17% incidence of diarrhea in the other groups. A significant shift in the diversity of gut flora was observed in only the BRAC group; it’s unfortunate that S. boulardii was not combined with quadruple therapy to determine if this shift would have been prevented. Yet in a previously published controlled clinical trial with 172 participants, S. boulardii was found to reduce both the incidence and duration of antibiotic-associated diarrhea when added to bismuth quadruple therapy, without influencing the eradication rate.
Although the addition of S. boulardii to triple therapy did not match the eradication rate of bismuth quadruple therapy in this more recent study, the reduction in adverse effects suggests it may be an important component of therapy, as suggested by many other clinical trials. For example, a randomized trial conducted among 194 children with H. pylori found that S. boulardii not only improved eradication rates when added to triple therapy (71.4% vs 61.9% with triple therapy alone, not significantly different), but only approximately 12% of children experienced diarrhea compared to 28% with triple therapy alone, a significant reduction. Additionally, compliance was also significantly higher (100% vs. 93%).
In a 2015 systematic review published in Alimentary Pharmacology & Therapeutics, an analysis of 11 randomized clinical trials with 2200 participants reported an eradication rate of 80% when S. boulardii was added to triple therapy, compared to 71% among people only receiving triple therapy, a small but significant increase in efficacy. S. boulardii was also associated with a significant 56% lower risk for adverse events, especially diarrhea (49% lower risk) and nausea (40% lower risk). The eradication rates and reduction in adverse events reported in this systemic review were graded as moderate in quality of evidence, and the reduction in diarrhea specifically was graded as based upon high-quality evidence.
In addition to complementary therapy, one clinical trial evaluated the use of S. boulardii as a monotherapy among H. pylori-positive participants. In this trial, 50 participants received only S. boulardii for 2 weeks, followed by a 4-week resting period before retesting. A control group of 50 received no treatment, only observation for 6 weeks. Upon retesting, approximately 30% of those receiving S. boulardii no longer tested positive for H. pylori, compared to approximately 2% in the control group. Participants testing positive then went on to receive bismuth quadruple therapy, and overall eradication rates were similar in both groups. This suggests that a small subset of patients may only require S. boulardii supplementation, though the majority would require additional treatment.
Another consideration is the development of antibiotic resistance following H. pylori therapy. A shotgun metagenomics study compared the effects of triple antibiotic therapy with and without S. boulardii on the expression of antimicrobial resistance genes (ARGs). The authors reported finding 641 unique ARGs in all fecal samples, associated with resistance to 18 classes of antibiotics, the most prevalent of which were against tetracyclines, MLS-B (macrolide, lincosamide, and streptogramin B), beta-lactams, and aminoglycosides. However, the addition of S. boulardii significantly reduced the abundance of ARGs, specifically against lincosamides, tetracyclines, MLS-B, and two genes in the beta-lactam class of antibiotics. Lastly, in a 2024 systematic review and meta-analysis of 29 randomized and controlled trials, probiotics were found to significantly enhance the gut’s colonization resistance (aka decolonize) against pathogenic organisms, such as C. difficile, with S. boulardii associated with the highest rate of decolonization (77%).
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