ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Antibiotic — Macrolide Pregnancy: Use with caution — limited data; considered acceptable for severe ENT infections in penicillin-allergic pregnant patients

Azithromycin

Brand names: Zithromax

Adult dose

Dose: 500 mg once daily for 3 days (upper RTI); 500 mg day 1 then 250 mg days 2–5 (sinusitis)
Route: Oral
Frequency: Once daily
Max: 500 mg/day
Used in ENT for penicillin-allergic patients: tonsillitis, sinusitis, otitis media. 3-day course delivers tissue levels lasting 5–7 days due to long half-life. Also effective for atypical organisms in sinusitis (Mycoplasma, Chlamydophila).

Paediatric dose

Dose: 10 mg/kg mg/kg
Route: Oral
Frequency: Once daily for 3 days
Max: 500 mg/day
BNFc: 6 months–17 years 10 mg/kg (max 500 mg) once daily for 3 days. Suspension available.

Dose adjustments

Renal

No dose adjustment required (mild-moderate); use with caution in severe renal impairment

Hepatic

Avoid in severe hepatic impairment

Paediatric weight-based calculator

BNFc: 6 months–17 years 10 mg/kg (max 500 mg) once daily for 3 days. Suspension available.

Clinical pearls

  • MHRA 2013: azithromycin prolongs QTc — avoid in patients with known QT prolongation, hypokalaemia, or on other QT-prolonging drugs
  • Excellent tissue penetration and intracellular accumulation — particularly effective against atypical pathogens in upper respiratory tract
  • 3-day course (1.5 g total) provides equivalent efficacy to 7-day conventional macrolides — long tissue half-life (~68 hours)
  • Do not use as empirical first-line for tonsillitis — reserve for penicillin-allergic patients; high rates of macrolide resistance in GAS in some regions
  • Clarithromycin preferred in UK primary care sinusitis — better local resistance profile; azithromycin for penicillin allergy

Contraindications

  • Macrolide hypersensitivity
  • QT prolongation or concomitant QT-prolonging drugs

Side effects

  • GI disturbance (nausea, diarrhoea)
  • QT prolongation
  • Cholestatic jaundice
  • Transient hearing loss (high doses, prolonged use)
  • Cardiac arrhythmia

Interactions

  • QT-prolonging drugs — additive QTc prolongation; avoid combination
  • Warfarin — increased INR (monitor)
  • Antacids — reduce peak concentration (take 1h before or 2h after)

Monitoring

  • QTc (in at-risk patients)
  • Symptom response
  • LFTs (prolonged use)

Reference: BNFc; BNF 90; BNFc; MHRA Drug Safety Update (2013) Azithromycin QT; NICE NG84. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways