Antibiotic (Macrolide) Pregnancy: B — generally considered safe

Azithromycin

Brand names: Zithromax

Adult dose

Dose: 500mg once daily × 3 days OR 500mg day 1 then 250mg days 2–5

Route: Oral or IV

Frequency: Once daily

Community-acquired pneumonia (IV): 500mg OD. STI (Chlamydia): 1g single dose. MAC prophylaxis: 1.25g weekly.

Dose: 10 mg/kg

Route: Oral

Frequency: Once daily × 3 days

Max: 500mg per dose

CAP: 10mg/kg/day OD × 3 days. Whooping cough (pertussis): <6 months 10mg/kg OD × 5 days; >6 months 10mg/kg day 1, then 5mg/kg days 2–5.

Paediatric weight-based calculator

Patient weight (kg)

CAP: 10mg/kg/day OD × 3 days. Whooping cough (pertussis): <6 months 10mg/kg OD × 5 days; >6 months 10mg/kg day 1, then 5mg/kg days 2–5.

Infant <6 weeks: associated with hypertrophic pyloric stenosis — AVOID if possible, use erythromycin alternative
Good intracellular penetration — excellent for atypicals: Mycoplasma, Chlamydophila, Legionella
Once-daily dosing and short course — excellent adherence for children
Check ECG if using with other QT-prolonging medications
Long-acting tissue concentrations (tissue half-life 2–4 days) — 3-day course equivalent to 7-day amoxicillin

QT-prolonging drugs (antipsychotics, clarithromycin, amiodarone) — additive QT prolongation
Warfarin — increased INR
Digoxin — increased levels

Reference: BNF for Children; PHE Antibiotic Guidelines; NICE NG138. Verify against your local formulary and the latest BNF before prescribing.

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways