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Macrolide antibiotic Pregnancy: Should only be used during pregnancy if clinically needed. Large observational data (>7000 exposed pregnancies) mostly do not suggest increased risk of major congenital or cardiovascular malformations; miscarriage evidence inconclusive. Excreted in human milk; weigh benefit of breast-feeding against therapy.

Azithromycin

Brand names: Zithromax

Azithromycin is a macrolide antibiotic indicated for a range of bacterial infections including respiratory tract, skin and soft-tissue, otitis media and certain sexually transmitted infections, valued for its convenient short courses.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 500 mg as a single dose on Day 1, then 250 mg once daily on Days 2–5 (total 1.5 g)
Route: Oral
Frequency: Once daily
Adult oral posology is taken from the US label because the UK SPC bundled here is a paediatric oral suspension (200 mg/5 ml) whose §4.2 covers only children <45 kg — verify the adult regimen against the appropriate UK adult SPC. US label by indication: community-acquired pneumonia (mild), pharyngitis/tonsillitis (second-line), uncomplicated skin/skin structure — 500 mg Day 1 then 250 mg once daily Days 2–5. Acute bacterial sinusitis — 500 mg once daily for 3 days. Acute bacterial exacerbation of COPD/chronic bronchitis — 500 mg once daily for 3 days OR 500 mg Day 1 then 250 mg once daily Days 2–5. Genital ulcer disease (chancroid), non-gonococcal urethritis/cervicitis — single 1 g dose. Gonococcal urethritis/cervicitis — single 2 g dose. Can be taken with or without food.

Paediatric dose

Dose: 10 mg/kg
Route: Oral
Frequency: Once daily
Max: Daily dose not to exceed adult 500 mg/day (except single-dose otitis media, max total 1500 mg); max total dose 1500 mg for any course except the 5-day streptococcal pharyngitis/tonsillitis regimen
UK SPC, paediatric patients aged 6 months and older weighing <45 kg, single daily dose. Acute bacterial sinusitis / community-acquired pneumonia / acute bacterial skin and skin structure infections: 10 mg/kg/day for 3 days, or 10 mg/kg on day 1 then 5 mg/kg/day on days 2–5. Acute bacterial otitis media: single dose of 30 mg/kg, or 10 mg/kg/day for 3 days, or 10 mg/kg day 1 then 5 mg/kg/day days 2–5. Acute streptococcal tonsillitis and pharyngitis: 20 mg/kg/day for 3 days, or 12 mg/kg/day for 5 days.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

UK SPC, paediatric patients aged 6 months and older weighing <45 kg, single daily dose. Acute bacterial sinusitis / community-acquired pneumonia / acute bacterial skin and skin structure infections: 10 mg/kg/day for 3 days, or 10 mg/kg on day 1 then 5 mg/kg/day on days 2–5. Acute bacterial otitis media: single dose of 30 mg/kg, or 10 mg/kg/day for 3 days, or 10 mg/kg day 1 then 5 mg/kg/day days 2–5. Acute streptococcal tonsillitis and pharyngitis: 20 mg/kg/day for 3 days, or 12 mg/kg/day for 5 days.

Verify in a children's formulary

Contraindications

  • Hypersensitivity to azithromycin, erythromycin, any macrolide or ketolide antibiotic, or any excipient
  • History of cholestatic jaundice/hepatic dysfunction associated with prior azithromycin use (US label)

Side effects

  • Diarrhoea
  • Nausea
  • Vomiting
  • Abdominal pain
  • Headache

Interactions

  • QT-prolonging drugs — increased risk of ventricular arrhythmia/torsades de pointes
  • Warfarin/oral anticoagulants — may potentiate effect; monitor prothrombin time
  • Nelfinavir — increased azithromycin concentrations; monitor for adverse reactions

Clinical monograph

How it works

It inhibits bacterial protein synthesis by binding to the 50S ribosomal subunit and preventing peptide chain elongation, conferring activity against many Gram-positive, atypical and some Gram-negative organisms.

Prescribing in practice

  • Because azithromycin can prolong the QT interval, avoid or use with caution in those with known QT prolongation, significant cardiac disease, electrolyte imbalance or other QT-prolonging medicines.
  • Rare but serious hepatotoxicity has been reported, and treatment should be stopped if signs of liver injury occur.
  • It may interact with drugs such as certain ergot alkaloids and statins, so concomitant therapy should be reviewed.

Monitoring

Routine monitoring is not usually required for short courses, but assess liver function and cardiac risk where clinically indicated.

Counselling the patient

  • Finish the full course as prescribed.
  • Seek advice if you develop palpitations, fainting or jaundice.
  • Let your clinician know about other medicines and any heart conditions.

Evidence & guidelines

Azithromycin is widely used across UK antimicrobial guidance, and the MHRA has issued reminders regarding its potential to prolong the QT interval.

Reference: NICE CKS; BTS pneumonia; BASHH; CF Trust; MHRA Drug Safety Update; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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