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Macrolide Antibiotic (Azalide) 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 used for a range of respiratory, skin and soft tissue, and sexually transmitted infections, valued for its long half-life and short treatment 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 binds the bacterial 50S ribosomal subunit, inhibiting protein synthesis, and is bacteriostatic against susceptible organisms with notable activity against atypical pathogens.

Prescribing in practice

  • It can prolong the QT interval, so use caution in those with existing QT prolongation, electrolyte disturbance, or taking other QT-prolonging drugs.
  • Use cautiously in significant hepatic impairment and discontinue if signs of liver dysfunction develop.
  • As a macrolide it interacts with several drugs and, like other antibiotics, carries a risk of Clostridioides difficile-associated diarrhoea.

Monitoring

Routine monitoring is not usually required for short courses; consider ECG and electrolytes where cardiac risk factors exist and monitor for hepatic or diarrhoeal adverse effects.

Counselling the patient

  • Complete the full prescribed course even if you feel better.
  • Report a fast or irregular heartbeat, fainting, or severe or persistent diarrhoea.
  • Tell the prescriber about all your other medicines.

Evidence & guidelines

Azithromycin is well established for specific indications in UK practice; macrolide use is guided by local microbiology and resistance considerations.

Reference: NICE CG191 (Pneumonia); BASHH Chlamydia Guidelines; BTS CAP Guidelines; 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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