Synopsis
Recognise SIBO as a syndrome arising from impaired clearance or altered anatomy, understand the limitations of breath and aspirate tests, identify nutrient and structural complications, and use short targeted antimicrobial courses with cause correction rather than indefinite empirical cycling.
- SIBO is an excess or abnormal composition of small-bowel microorganisms causing symptoms or malabsorption; bloating alone is too nonspecific to establish it.
- Predisposing mechanisms include blind loops, strictures, fistulae, diverticula, scleroderma dysmotility, previous surgery, small-bowel stasis and loss of gastric acid or ileocaecal barrier.
- Symptoms include bloating, discomfort, diarrhoea, steatorrhoea, weight loss and B12 or fat-soluble vitamin deficiency; methane-associated overgrowth may present with constipation.
- Jejunal aspirate culture is invasive and lacks fully standardised thresholds; glucose and lactulose breath tests have important false-positive and false-negative limitations.
- BSG chronic-diarrhoea guidance favours an empirical antibiotic trial when pre-test probability is high rather than relying on poorly performing routine breath tests.
- A treatment response does not prove SIBO because antibiotics alter colonic flora, inflammation and motility; document what changed and whether it recurs.
- Correct a stricture, blind loop, fistula, medicine driver or motility problem where possible, and avoid repeated antibiotics without anatomical review.
- Replace B12 and other deficits, review nutrition and consider refeeding risk in severe disease.
Key red flags
Persistent vomiting, colicky focal pain, peritonism, fever or lactate elevation is not uncomplicated SIBO and requires urgent imaging and surgical assessment.
Investigation priorities
Obtain operation and radiotherapy history, assess strictures, fistulae, diverticula, dysmotility and review opioids, anticholinergics and acid suppression.
Management branches
Compatible symptoms occur with clear structural, surgical or motility risk.
- Exclude acute obstruction, ischaemia and sepsis, then document anatomy, medicine drivers, stool, weight and deficiency phenotype.
- Discuss a local validated test or a time-limited empirical antibiotic trial with gastroenterology, defining the expected symptom and nutritional response.
- Correct measured deficiencies and optimise diet without imposing multiple unsupported exclusions.
- Arrange imaging or endoscopy when anatomy has not been assessed or a correctable lesion is plausible.
Key medicines
RifaximinSpecialist-selected short oral course using the current local off-label or formulary regimen; dose and duration vary by phenotype and service.Not a universal first-line choice and not proof of diagnosis. Cost, resistance, C. difficile, recurrence and interactions require review; avoid endless repeat prescriptions.
Alternative systemic antibioticA short course of an agent such as co-amoxiclav, metronidazole or another locally approved choice, adjusted for renal function, allergy and previous cultures.Agent-specific neuropathy, tendon, hepatic, interaction and C. difficile risks. Choose with microbiology and reassess rather than rotate empirically.