Exploring effectiveness of Metronidazole, Bismuth, and Rifaximin in treating small intestinal bacterial overgrowth and irritable bowel syndrome: A systematic review

Abstract

BACKGROUND

Small intestinal bacterial overgrowth (SIBO) and irritable bowel syndrome (IBS) are common gastrointestinal disorders that significantly impact patients' quality of life and pose a financial burden on healthcare systems. SIBO is characterized by an abnormal increase in small intestinal bacteria, leading to symptoms such as malabsorption, diarrhea, bloating, and abdominal pain. IBS is a functional gastrointestinal disorder marked by recurrent abdominal pain with changes in bowel habits, and is subclassified into diarrhea-predominant IBS (IBS-D), constipation-predominant IBS (IBS-C), and mixed-type IBS. Notably, SIBO and IBS—particularly IBS-D—often present with overlapping symptoms. Antibiotics such as Metronidazole, Bismuth, and Rifaximin are commonly used to treat both conditions; however, their comparative efficacy and safety remain unclear.

AIM

To analyze and compare the role of Metronidazole, Bismuth, Rifaximin for improvement of SIBO and IBS.

METHODS

A systematic review was performed on the databases PubMed and Cochrane Library, spanning from 2000 to 2023. Studies eligible for inclusion were observational studies or randomized controlled trials (RCTs) performed on human subjects that examined the use of Metronidazole, Bismuth, or Rifaximin in the management of SIBO and IBS. Two independent reviewers performed data extraction, and resolved discrepancies by consensus. The data extracted consisted study characteristics, patient demographics, intervention details, and outcome measured. Key references were verified and prioritized using Reference Citation Analysis to ensure contemporary relevance and citation impact.

RESULTS

A total of 55 studies, including RCTs and observational studies, met inclusion criteria and were analyzed. These studies assessed the efficacy and safety of Metronidazole, Bismuth, and Rifaximin in patients with SIBO and IBS. Rifaximin demonstrated the most consistent efficacy across both conditions, particularly in IBS-D and mild to moderate SIBO, with a low incidence of adverse events (16.7%). Metronidazole showed moderate efficacy, with some benefit in IBS-C and mild SIBO, but was associated with a higher rate of gastrointestinal side effects (16.6%). Bismuth offered symptom relief in IBS, especially for bloating and diarrhea, though its effectiveness was generally lower than the other agents. Subgroup analyses suggested differential efficacy by IBS subtype and SIBO severity, supporting the potential role of clinical phenotype in guiding antibiotic selection.

CONCLUSION

Significant clinical efficacy was shown by the drug Rifaximin among IBS-D patients at reducing symptoms, with minimal undesirable adverse effects and a favorable safety profile. Metronidazole was effective in treating SIBO but was generally associated with a higher prevalence of gastrointestinal side effects than the other drugs. However, Bismuth generally proved to be effective on isolated levels, especially in combination regimes where it showed its efficacy levels to be less pronounced relative to Rifaximin as well as Metronidazole. Further studies are needed to optimize treatment strategies and clarify the comparative long-term benefits and risks of these therapies.

Keywords: Small intestinal bacterial overgrowth; Irritable bowel syndrome; Rifaximin; Metronidazole; Bismuth

Core Tip: This study compares the efficacy and safety of Metronidazole, Bismuth, and Rifaximin in managing small intestinal bacterial overgrowth (SIBO) and irritable bowel syndrome (IBS). Rifaximin showed the greatest clinical benefit, particularly in diarrhea-predominant IBS patients, with minimal side effects. Metronidazole was effective for SIBO but associated with higher gastrointestinal side effects. Bismuth demonstrated some effectiveness, particularly in combination therapies, but was less pronounced than the other two antibiotics. Further research is needed to optimize treatment strategies and assess long-term outcomes.