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Macrolide Antibiotic (Azalide) Pregnancy: Generally considered safe — azithromycin is the macrolide of choice in pregnancy when one is needed (more safety data than clarithromycin). RCOG recommends for Chlamydia and CAP in pregnancy.

Azithromycin

Brand names: Zithromax

Adult dose

Dose: Community-acquired pneumonia (non-severe): 500mg OD for 3–5 days (or 500mg on day 1, then 250mg OD for 4 days). Chlamydia trachomatis: 1g as single dose. Mild COPD exacerbation (atypical cover): 500mg OD for 3 days. Skin/soft tissue infection: 500mg OD for 3 days.
Route: Oral
Frequency: Once daily
Max: 500mg OD
Azalide macrolide — longer tissue half-life than clarithromycin (tissue half-life ~68h); accumulates in phagocytes. Once-daily dosing and shorter courses. Less CYP3A4 inhibition than clarithromycin — safer drug interaction profile. Preferred macrolide in pregnancy (more safety data), in elderly, and when drug interactions with clarithromycin are a concern.

Paediatric dose

Dose: 10 mg/kg
Route: Oral
Frequency: Once daily
Max: 500mg OD
BNFc: 6 months–17 years: 10mg/kg OD (max 500mg) for 3–5 days. Chlamydia: 1g single dose (adolescents). Seek paediatric specialist opinion for severe infections. Pyloric stenosis reported in infants under 6 weeks — avoid in this age group.

Dose adjustments

Renal

No dose adjustment required — primarily biliary excretion.

Hepatic

Severe hepatic impairment: use with caution — primarily hepatically excreted; accumulation risk.

Paediatric weight-based calculator

BNFc: 6 months–17 years: 10mg/kg OD (max 500mg) for 3–5 days. Chlamydia: 1g single dose (adolescents). Seek paediatric specialist opinion for severe infections. Pyloric stenosis reported in infants under 6 weeks — avoid in this age group.

Clinical pearls

  • Safer drug interaction profile than clarithromycin — does not significantly inhibit CYP3A4; does not cause the same statin, colchicine, or warfarin interactions as clarithromycin
  • Preferred macrolide in pregnancy — more human safety data than clarithromycin; RCOG recommends azithromycin for Chlamydia in pregnancy (1g single dose)
  • QT prolongation: still a concern — avoid in patients with long QT syndrome or taking QT-prolonging drugs; obtain ECG if concerned
  • Tissue persistence: tissue concentrations remain therapeutic for 5–7 days after a 3-day course — explains why short courses are effective; no need to continue longer for most community infections

Contraindications

  • QT prolongation or risk factors
  • Hypersensitivity to macrolides
  • Jaundice from prior azithromycin use (cholestatic hepatitis)

Side effects

  • GI upset, nausea, diarrhoea (common — less than clarithromycin)
  • QTc prolongation (dose-related)
  • Hepatotoxicity (rare — cholestatic jaundice)
  • Hearing loss (very rare — high doses)
  • C. difficile (antibiotic-associated)
  • Hypersensitivity reactions

Interactions

  • QT-prolonging drugs — additive risk (less than clarithromycin but still present)
  • Antacids (aluminium/magnesium) — reduce absorption; separate by 1–2h
  • Warfarin — modest increase in INR; monitor
  • Digoxin — mild increase in levels

Monitoring

  • Symptom resolution (48–72h)
  • LFTs if jaundice or previous hepatitis with macrolides
  • QTc if cardiac risk factors

Reference: BNFc; BNF 90; NICE CG191 (Pneumonia); BASHH Chlamydia Guidelines; BTS CAP Guidelines. Verify against your local formulary and the latest BNF before prescribing.

Related

Curated clinical cross-links plus same-class fallbacks.

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