The gut microbiota is intrinsically linked to human health; disturbances in microbial homeostasis are implicated in both intestinal and extraintestinal disorders. Probiotics are “live microorganisms that, when administered in adequate amounts, confer a health benefit on the host,” and many commercial preparations comprising a diverse range of species are available. While probiotics have been much researched, better understanding of the probiotic effects and applications of species such as Bacillus clausii is warranted. In this narrative literature review, we review the characteristics and mechanisms of action supporting B. clausii as a probiotic and discuss the evidence from clinical studies evaluating B. clausii probiotics for the management of a variety of gastrointestinal disorders and symptoms in children and adults. Finally, we highlight the challenges of future research and the need for more robust and diverse clinical evidence to guide physicians in the clinical application of probiotics for gastrointestinal disorders and other conditions. Supplementary Information The online version contains supplementary material available at 10.1007/s12325-022-02285-0.

Objectives Current irritable bowel syndrome (IBS) treatments have limited efficacy and probiotics like Bacillus clausii ( B. clausii ) were found to be effective in the management of several gastrointestinal disorders. This phase III trial assessed the efficacy and safety of adding B. clausii (four strains: O/C, N/R, SIN, T), versus placebo, to conventional treatment of pediatric IBS in Mexico. Methods Patients aged 6–17 years 11 months with IBS (Rome IV) for at least 2 months were randomized to receive either B. clausii (oral suspension, total dose 4 billion spores/day) or placebo once daily for 8 weeks. All patients also received conventional treatment. The primary endpoint was the difference in the proportion of patients with clinical improvements at Week 8 (Global Assessment Questions [GAQ]). Secondary endpoints included responders by Subject’s Global Assessment of Relief for Children with IBS (SGARC); number/consistency of stools; abdominal distention/bloating; abdominal pain/intensity; and IBS behavior. Results 73.6% (95% confidence interval [CI] 67.3–80.0; B. clausii n = 129) and 78.5% (95% CI 72.5–84.4; placebo n = 130) of patients had symptom improvement ( p = 0.8182). For Week 8 SGARC, 19.2% ( B. clausii ) and 20.9% (placebo) reported complete symptom relief. Stool evaluations, bloating, abdominal pain/intensity, and IBS behavior were similar between groups. Both treatments were well tolerated. Conclusion No significant differences in efficacy between B. clausii and placebo were demonstrated in addition to conventional treatment. The sample size calculation was based on an expected placebo/conventional treatment response of 30–40%. However, the actual treatment response observed was 80% and, thus, a study with larger population would be warranted. In addition, this study was conducted during the COVID-19 pandemic, when such controlled social conditions may have resulted in better diet, greater family stability, less psychological stress, and lower risk of infections exacerbating IBS, thereby improving symptoms in both groups. EudraCT number 2018-004519-31. Supplementary Information The online version contains supplementary material available at 10.1007/s40272-022-00536-9.

In patients with hyponatremic dehydration episodes with hypokalaemic hypochloraemic metabolic alkalosis, PBS should be considered as differential diagnosis. CF could be presented as PBS, mainly in patients younger than 2 years.

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