From the Guidelines
Small intestinal bacterial overgrowth (SIBO) is a condition where excessive bacteria colonize the small intestine, causing various digestive symptoms, and its management should prioritize reducing morbidity, mortality, and improving quality of life. The three main types of SIBO are hydrogen-dominant, methane-dominant (also called intestinal methanogen overgrowth or IMO), and hydrogen sulfide-dominant, each with distinct symptoms and treatment approaches 1.
- Hydrogen-dominant SIBO typically causes diarrhea, bloating, abdominal pain, and excessive gas.
- Methane-dominant SIBO often presents with constipation, bloating, and abdominal discomfort.
- Hydrogen sulfide-dominant SIBO is characterized by sulfur-smelling gas, diarrhea, and sometimes urgency. Common symptoms across all types include bloating, abdominal distension, excessive flatulence, abdominal pain or discomfort, altered bowel habits, nausea, fatigue, and nutrient deficiencies (particularly vitamin B12, iron, and fat-soluble vitamins) 1.
Treatment Approaches
Treatment usually includes antibiotics (like rifaximin), antimicrobials, dietary modifications (such as low FODMAP diet), and addressing underlying causes such as motility disorders, structural abnormalities, or immunodeficiencies that may have contributed to bacterial overgrowth in the first place 1.
- Rifaximin is often the first choice for treating SIBO due to its efficacy and safety profile, as it can reduce bacterial overgrowth and improve symptoms without the risk of systemic absorption 1.
- Other antibiotics such as metronidazole, amoxicillin-clavulanate, doxycycline, and norfloxacine may also be used, but with caution due to the risk of resistance and side effects 1.
- Dietary modifications, such as a low FODMAP diet, can also help alleviate symptoms and improve quality of life 1.
Diagnosis and Management
Diagnosis typically involves breath testing that measures hydrogen and methane gases after consuming a test substrate, and management should involve a multidisciplinary approach to address underlying causes and prevent complications 1.
- Sequential antibiotic therapy is very effective in treating intestinal bacterial overgrowth and reducing malabsorption, and can also improve nutritional status and sometimes bloating 1.
- Poorly absorbable antibiotics such as aminoglycosides and rifaximine are preferred, but alternating cycles with metronidazole and tetracycline may be necessary to limit resistance 1.
From the Research
Types of SIBO
- There are different types of SIBO, including hydrogen-dominated, methane-dominated, and mixed SIBO 2
- The type of SIBO can affect the symptoms and treatment outcomes 3, 4
Symptoms of SIBO
- Common symptoms of SIBO include abdominal distension, bloating, diarrhea, and gas formation 2
- Other symptoms may include abdominal pain, bowel movements, and extraintestinal symptoms 5, 3
- The symptoms of SIBO can overlap with other gastrointestinal disorders, making diagnosis challenging 2
SIBO Subtypes and Symptoms
- Hydrogen-dominated SIBO is often associated with diarrhea as the dominant symptom 4
- Methane-dominated SIBO is often associated with constipation as the dominant symptom 4
- Mixed SIBO can present with a combination of symptoms, including bloating, gas, and abdominal pain 3, 4
Diagnosis and Treatment
- The diagnostic gold standard for SIBO is small bowel aspirate and culture, but glucose and lactulose breath testing are more commonly used due to their noninvasive nature and low cost 2
- Treatment for SIBO typically involves a prolonged course of oral antibiotics, but alternative therapies such as probiotics, therapeutic diets, and herbal medicines are being explored 5, 3, 6