Antibiotic — Macrolide 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, ENT, certain sexually transmitted and other infections, which allows 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: Acute bacterial sinusitis: 500 mg once daily for 3 days. Pharyngitis/tonsillitis (second-line): 500 mg Day 1 then 250 mg once daily Days 2–5

Route: Oral

Frequency: Once daily

ENT-relevant adult regimens shown; 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: acute bacterial sinusitis — 500 mg once daily for 3 days. Pharyngitis/tonsillitis (second-line therapy) — 500 mg Day 1 then 250 mg once daily Days 2–5. Other indications for context: community-acquired pneumonia / uncomplicated skin — 500 mg Day 1 then 250 mg Days 2–5; acute bacterial exacerbation of COPD/chronic bronchitis — 500 mg once daily for 3 days OR 500 mg Day 1 then 250 mg Days 2–5. 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. ENT-relevant: 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. Acute bacterial sinusitis — 10 mg/kg/day for 3 days, or 10 mg/kg day 1 then 5 mg/kg/day days 2–5 (same regimen as community-acquired pneumonia and skin/skin structure infections).

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

Patient weight (kg)

Verify in a children's formulary

US labelling (FDA)

Reference — US labelling, may differ from UK

• Adult Patients ( ) Infection Recommended Dose/Duration of Therapy Community-acquired pneumonia (mild severity) Pharyngitis/tonsillitis (second-line therapy) Skin/skin structure (uncomplicated) 500 mg as a single dose on Day 1, followed by 250 mg once daily on Days 2 through 5. Acute bacterial exacerbations of chronic bronchitis (mild to moderate) 500 mg as a single dose on Day 1, followed by 250 mg once daily on Days 2 through 5 or 500 mg once daily for 3 days. Acute bacterial sinusitis 500 mg once daily for 3 days. Genital ulcer disease (chancroid) Non-gonococcal urethritis and cervicitis One single 1 gram dose. Gonococcal urethritis and cervicitis One single 2 gram dose. • Pediatric …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2026-03-16. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

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 at the 50S ribosomal subunit.

Prescribing in practice

It prolongs the QT interval — use caution with other QT-prolonging drugs and in electrolyte disturbance.
It has fewer CYP interactions than clarithromycin, but not none.
Its long half-life means the antibacterial effect persists after the short course ends.

Monitoring

Short courses need no routine monitoring; consider ECG/electrolytes where QT risk is high.

Counselling the patient

Complete the (often short) course.
Gastrointestinal upset is common.
Tell your clinician about heart-rhythm problems or other medicines.

Evidence & guidelines

Used per local antimicrobial guidance, valued for short courses; QT precautions apply.

Reference: MHRA Drug Safety Update (2013) Azithromycin QT; NICE NG84; 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).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways