Abstract
Diarrhea is common in critically ill patients and can lead to malnutrition, electrolyte imbalance, and dehydration. While its direct impact on outcomes, such as mortality or intensive care unit (ICU) stay, remains unclear due to inconsistent definitions, it often results from drug-induced causes, such as antibiotics and antacids. These agents can also contribute to dysbiosis and increase the risk of infections including Clostridioides difficile infections (CDI) and ventilator-associated pneumonia (VAP).Probiotics, defined as live beneficial microorganisms, can counteract dysbiosis by modulating immune responses, restoring microbial balance, and reducing intestinal inflammation. Evidence suggests that probiotics may help prevent diarrhea and secondary infections. Clinical trials and meta-analyses have shown that probiotics may reduce the incidence of VAP, length of ICU stay, duration of mechanical ventilation, and potential in-hospital mortality in critically ill patients.However, evaluating probiotic efficacy remains challenging due to the lack of standardized markers and the influence of confounding factors like antacid use. In a randomized controlled trial, synbiotic therapy was associated with improved fecal microbiota and reduced infections; however, the role of antacids was not addressed.Probiotics are generally safe, although rare adverse events, such as probiotic-associated bacteremia, have been reported, particularly in immunocompromised individuals.The 2024 Japanese Critical Care Nutrition Guidelines included a systematic review and meta-analysis supporting the potential benefits of probiotics in critically ill patients. However, due to significant heterogeneity in strains, dosing, duration, and concurrent antibiotic/antacid use, a weak recommendation (GRADE 2C; low certainty) was issued.Future research should focus on the standardized evaluation of diarrhea and microbiota changes, the use of objective markers-such as fecal pH and short-chain fatty acid levels-and clarification of the interactions of probiotics with other medications. Comprehensive bowel management, including the cautious use of antibiotics and antacids, may be essential to fully recognize the therapeutic potential of probiotics in critical care settings.