Azithromycin in diarrhoeal illness
When it is useful, how to dose it, and key safety considerations
What is azithromycin?
Azithromycin is a macrolide antibiotic used for several invasive bacterial causes of diarrhoea. It is often preferred for severe traveller’s diarrhoea where fluoroquinolone resistance is common.
When azithromycin is appropriate
- Severe traveller’s diarrhoea (incapacitating symptoms, fever, dysentery)
- Suspected/confirmed Campylobacter or Shigella
- High-risk patients with significant illness
When azithromycin should NOT be used
- Likely viral gastroenteritis
- Mild illness improving
- Suspected STEC — risk of HUS
Typical adult dosing (general guidance)
- Single dose: 1,000 mg once
- Short course: 500 mg once daily for 1–3 days
Exact regimen depends on severity, organism, and local guidance.
Important safety considerations
Heart rhythm effects
Azithromycin can prolong the QT interval. Use caution with long QT syndrome, heart disease, electrolyte disturbance, or other QT-prolonging medications.
Common medications that prolong the QT interval
- Antibiotics: clarithromycin, erythromycin; fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin)
- Antiemetics: ondansetron (especially IV/high doses), domperidone
- Psychiatric: citalopram, escitalopram; antipsychotics (haloperidol, quetiapine, ziprasidone)
- Cardiac: amiodarone, sotalol
Other risk factors: low potassium/magnesium (common in diarrhoea), severe dehydration, congenital long QT.
Allergy and anaphylaxis
Any history of antibiotic anaphylaxis should be documented clearly.
Key takeaway: Azithromycin is a targeted option for severe or invasive diarrhoeal illness, especially in travellers. It should not be used routinely without clear indication.