Antibiotics in diarrhoea
When they help, when they harm, and how to choose safely
Core principle: Most diarrhoea does not benefit from antibiotics.
- Do not shorten viral illness
- Increase side effects and allergic reactions
- Increase risk of C. diff
- Drive antimicrobial resistance
Situations where antibiotics may be appropriate
- Severe traveller’s diarrhoea (incapacitating symptoms, fever, dysentery)
- Suspected/confirmed invasive bacterial infection
- Cholera with severe dehydration (adjunct to fluids)
- High-risk hosts
Situations where antibiotics should be avoided
- Likely viral gastroenteritis
- Mild illness improving
- Suspected STEC — risk of HUS
- Unexplained diarrhoea without red flags
Commonly used antibiotics (overview)
| Antibiotic | Typical role | Key cautions |
|---|---|---|
| Azithromycin | Severe traveller’s diarrhoea, dysentery | QT prolongation, interactions |
| Rifaximin | Non-invasive traveller’s diarrhoea | Not for invasive disease |
| Ciprofloxacin / fluoroquinolones | Limited modern role | Tendon rupture, neuropathy, aortic risk |
| Metronidazole | Giardia, amoebiasis | Neuropathy, alcohol interaction |
| Oral vancomycin / fidaxomicin | C. diff | Reserved for confirmed infection |
Major risks to consider before prescribing
Allergy and anaphylaxis
Any history of anaphylaxis must be documented clearly.
Antibiotic-associated diarrhoea and C. diff
Any antibiotic can trigger C. diff; risk rises with age, hospitalisation, immunosuppression.
Fluoroquinolone-specific risks
Fluoroquinolones carry boxed warnings including tendon rupture, neuropathy, CNS effects, aortic aneurysm/dissection risk.
Key takeaway: Antibiotics are a precision tool, not a default response. Used correctly, they help. Used casually, they cause harm.