Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
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 with a long tissue half-life, used for respiratory, skin and soft-tissue, and certain sexually transmitted and atypical infections, and prophylactically in some chronic respiratory conditions.

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); STIs: single 1 g (2 g for gonococcal)
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) and 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 binds the bacterial 50S ribosomal subunit and inhibits protein synthesis by blocking translocation, giving bacteriostatic and, at higher concentrations, bactericidal activity against susceptible organisms.

Prescribing in practice

  • Azithromycin can prolong the QT interval, so it should be used with caution in patients with cardiac risk factors, electrolyte disturbance, or concomitant QT-prolonging drugs.
  • It carries a recognised risk of hepatotoxicity and should be reviewed if signs of liver dysfunction develop.
  • Long courses for respiratory prophylaxis warrant consideration of macrolide resistance and hearing assessment.

Monitoring

Monitor liver function and, where there is cardiac risk or prolonged use, ECG, electrolytes and hearing as appropriate.

Counselling the patient

  • Complete the prescribed course even if you feel better.
  • Report palpitations, fainting, or yellowing of the skin or eyes.
  • Tell your clinician about any heart-rhythm problems or other medicines you take.

Evidence & guidelines

Azithromycin features in UK antimicrobial guidance for various infections, with the MHRA having highlighted its association with QT-interval prolongation.

Reference: BASHH STI Guidelines; RECOVERY Trial (Horby et al, NEJM 2021); 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.

Calculators
Drugs
Pathways