Small intestinal bacterial overgrowth (SIBO): Brazilian guidelines 2025

Small intestinal bacterial overgrowth (SIBO): Brazilian guidelines 2025

Small intestinal bacterial overgrowth (SIBO) is a condition characterized by an excessive bacterial population in the small intestine, often involving microbes typically found in the large intestine. This dysbiosis leads to symptoms such as bloating, diarrhea, abdominal pain, and malnutrition, significantly impairing patients’ quality of life. Despite its clinical relevance, SIBO remains underdiagnosed and poorly understood, particularly in Brazil, where epidemiological data and standardized guidelines are scarce. This article explores the pathophysiology, diagnosis, and treatment of SIBO, with a focus on the 2025 Brazilian guidelines.

Pathophysiology and risk factors

SIBO arises from an imbalance in the small intestine’s microbial ecosystem, often due to disruptions in gastrointestinal motility, secretory function, or immune defenses. Key risk factors include:

1. Gastrointestinal Motility Disorders: Conditions like diabetes or chronic opioid use can impair the migrating motor complex (MMC), leading to bacterial stagnation.
2. Reduced Gastric Acid Secretion: Proton pump inhibitors (PPIs) and hypochlorhydria reduce stomach acidity, facilitating bacterial overgrowth.
3. Structural Abnormalities: Strictures, diverticula, or surgical alterations (e.g., Roux-en-Y gastric bypass) create environments conducive to bacterial stasis.
4. Immune Dysfunction: Impaired gut immunity, including deficiencies in secretory IgA, can predispose individuals to SIBO.

SIBO frequently coexists with other gastrointestinal disorders, such as irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and celiac disease, complicating diagnosis and management.

Epidemiology

Globally, SIBO prevalence ranges from 2.5% to 22%, with higher rates among older adults and individuals with comorbidities. In Brazil, limited studies suggest a significant burden, particularly among vulnerable populations. For example, a study found a 30% prevalence of SIBO in Brazilian Crohn’s disease patients, while another reported rates of 56% and 64% in patients with gastrointestinal symptoms using breath tests. However, the lack of standardized diagnostic criteria and testing methods complicates epidemiological research.

Clinical presentation

SIBO presents with nonspecific symptoms, including bloating, abdominal pain, diarrhea, and weight loss. Diarrhea is the symptom most strongly associated with SIBO. Severe cases may lead to malnutrition, nutrient deficiencies, and neurological symptoms like brain fog. Given the overlap with other gastrointestinal disorders, SIBO should be suspected in patients with risk factors such as motility disorders, altered GI anatomy, or immune deficiencies.

Diagnosis

Diagnosing SIBO requires objective testing due to the nonspecific nature of symptoms. The gold standard is small bowel aspirate culture, with thresholds of ≥10⁵ CFU/mL for jejunal aspirate and ≥10³ CFU/mL for duodenal aspirate. However, this method is invasive, expensive, and not widely available.

Breath testing, which measures hydrogen (H₂) and methane (CH₄) produced by bacterial fermentation, is the preferred non-invasive diagnostic tool. A rise of ≥20 ppm in H₂ or ≥10 ppm in CH₄ from baseline within 90 minutes indicates a positive result. Despite its practicality, breath testing lacks standardization, and the interpretation of results can vary.

Treatment

The treatment of SIBO is multifaceted, aiming to address the underlying bacterial overgrowth, alleviate symptoms, and prevent recurrence. The cornerstone of therapy involves the use of antibiotics, but dietary modifications, probiotics, and management of predisposing conditions also play critical roles. Below is a detailed elaboration on the treatment strategies for SIBO.

1. Identifying and Addressing Underlying Causes

The initial step in managing SIBO involves identifying and addressing the root causes that contribute to bacterial overgrowth. These may include:

• Motility Disorders: Conditions like diabetes or chronic opioid use can impair gut motility, leading to bacterial stagnation. Prokinetic agents such as prucalopride or low-dose erythromycin may be used to improve motility.
• Reduced Gastric Acid: Proton pump inhibitors (PPIs) and hypochlorhydria reduce stomach acidity, creating an environment conducive to bacterial overgrowth. Reducing or discontinuing PPI use, when possible, is recommended.
• Structural Abnormalities: Strictures, diverticula, or surgical alterations (e.g., Roux-en-Y gastric bypass) may require surgical correction to prevent bacterial stasis.
• Nutritional Deficiencies: Patients with SIBO often suffer from malabsorption of fat-soluble vitamins (A, D, E, K) and vitamin B12. Supplementation of these nutrients is essential to address deficiencies and support overall health.

2. Antibiotic Therapy: The Cornerstone of SIBO Treatment

Antibiotics remain the primary treatment for SIBO, as they directly target and reduce bacterial overgrowth in the small intestine. A recent meta-analysis involving 196 patients demonstrated that antibiotics significantly improve symptoms, with a pooled response rate of 49.5% compared to 13.7% in untreated patients. The number needed to treat (NNT) for symptom relief was 2.8, underscoring the efficacy of antibiotic therapy.

a. Rifaximin

• First-Line Treatment: Rifaximin, a non-absorbable antibiotic, is the preferred choice for SIBO due to its localized action, minimal systemic side effects, and low risk of antibiotic resistance.
• Efficacy: Studies show a 59% eradication rate for SIBO, with higher success rates in hydrogen-dominant cases.
• Dosage: 550 mg three times daily for 14 days.

b. Neomycin

• For Methane-Dominant SIBO: Neomycin is often used in combination with rifaximin to target methane-producing Archaea.
• Dosage: 500 mg twice daily for 14 days.
• Considerations: Potential side effects include ototoxicity and nephrotoxicity, requiring cautious use in patients with kidney impairment.

c. Other Antibiotics

• Ciprofloxacin: Effective for hydrogen-dominant SIBO, with studies showing normalization of breath tests and symptom improvement in 83% of patients.
• Metronidazole: Often used for methane-dominant SIBO, either alone or in combination with rifaximin.
• Amoxicillin-Clavulanate: An alternative for hydrogen-dominant SIBO, particularly in cases where rifaximin is unavailable.

d. Combination Therapy

• For methane-dominant SIBO, a combination of rifaximin and neomycin is the most effective regimen, with eradication rates of up to 87%.

3. Special Considerations in Resource-Limited Settings

In underserved areas where access to diagnostic tests is limited, empirical treatment with antibiotics may be considered for patients with high clinical suspicion of SIBO. Systemic antibiotics like ciprofloxacin or metronidazole are recommended alternatives when rifaximin is unavailable. However, close monitoring of treatment response is essential to avoid unnecessary or prolonged antibiotic use.

4. Managing Recurrence

Recurrence is a common challenge in SIBO management, with rates as high as 43.7% within 9 months of treatment. Factors contributing to recurrence include impaired gut motility, anatomical abnormalities, and chronic PPI use. Strategies to prevent recurrence include:

• Cyclic Antibiotic Therapy: Repeated courses of antibiotics may be necessary for recurrent cases.
• Prokinetics: Nightly use of low-dose prokinetics like prucalopride or erythromycin can help maintain gut motility and prevent bacterial overgrowth.
• Addressing Predisposing Conditions: Managing underlying conditions such as diabetes or autoimmune disorders is crucial for long-term success.

5. Role of Probiotics

The use of probiotics in SIBO treatment remains controversial. While some studies suggest benefits, others indicate that probiotics may exacerbate symptoms or even contribute to bacterial overgrowth. Key findings include:

• Mixed Evidence: A meta-analysis of 18 studies reported a 1.6-fold increase in SIBO clearance with probiotics, but the studies were small and of poor quality.
• Potential Risks: Probiotics may cause SIBO or D-lactic acidosis in some patients, leading to symptoms like gas and bloating.
• Adjuvant Therapy: Probiotics like Saccharomyces boulardii may be beneficial when used alongside antibiotics, but routine use is not recommended due to inconsistent evidence.

6. Dietary Modifications

Diet plays a supportive role in managing SIBO symptoms and preventing recurrence. However, dietary strategies should be individualized and used in conjunction with antibiotic therapy.

a. Low-FODMAP Diet

• Mechanism: Reduces fermentable carbohydrates that feed bacteria in the small intestine.
• Efficacy: Effective in alleviating symptoms like bloating and abdominal pain in the short term.
• Limitations: Long-term use can negatively impact gut microbiota diversity and is not recommended beyond 6 weeks.

b. Specific Carbohydrate Diet (SCD)

• Mechanism: Eliminates complex carbohydrates that are difficult to digest, reducing bacterial fermentation.
• Efficacy: May help some patients, but evidence is limited.

c. Elemental Diet

• Mechanism: Provides nutrition in a pre-digested form, starving bacteria in the small intestine.
• Efficacy: Highly effective for SIBO eradication, with success rates of up to 80-85%.
• Limitations: Difficult to adhere to due to poor palatability and high cost.

d. Long-Term Dietary Strategies

• After SIBO eradication, a balanced diet rich in soluble fiber and polyphenols can support a healthy gut microbiome. Avoid excessive consumption of fermentable carbohydrates and processed foods.

The treatment of SIBO requires a comprehensive approach that combines antibiotic therapy, dietary modifications, and management of underlying predisposing factors. Rifaximin remains the first-line treatment for hydrogen-dominant SIBO, while combination therapy with neomycin is preferred for methane-dominant cases. Addressing recurrence and tailoring treatment to individual patient needs are essential for long-term success. In resource-limited settings, empirical treatment with systemic antibiotics may be necessary, but close monitoring is crucial to avoid overuse. Probiotics and dietary interventions can provide symptomatic relief, but their role remains controversial and requires further research.

Challenges in Brazil

In Brazil, the management of SIBO faces several challenges, including limited access to diagnostic tests, a lack of standardized guidelines, and insufficient local epidemiological data. These gaps result in heterogeneous treatment protocols and disparities in care. To address these issues, there is an urgent need for national coordination and adherence to standardized guidelines, ensuring uniform care and improved patient outcomes.

Conclusion

SIBO is a complex condition with significant implications for patient health and quality of life. While breath testing and antibiotic therapy offer effective diagnostic and treatment pathways, challenges remain in standardizing care, particularly in Brazil. Enhanced research, improved diagnostic tools, and tailored treatment strategies are essential to optimize SIBO management and address the unique needs of the Brazilian population. By fostering collaboration among healthcare providers and researchers, Brazil can bridge the gaps in SIBO care and improve outcomes for affected individuals.

Reference

1. Silva BCD, Ramos GP, Barros LL, Ramos AFP, Domingues G, Chinzon D, Passos MDCF. DIAGNOSIS AND TREATMENT OF SMALL INTESTINAL BACTERIAL OVERGROWTH: AN OFFICIAL POSITION PAPER FROM THE BRAZILIAN FEDERATION OF GASTROENTEROLOGY. Arq Gastroenterol 2025 Feb 17;62:e24107.