Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Antibiotic (Macrolide)

Azithromycin

Brand names: Zithromax

Azithromycin is a macrolide antibiotic used in children for respiratory tract infections, certain atypical and sexually transmitted infections, and pertussis, with a long tissue half-life allowing short courses.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

It binds the bacterial 50S ribosomal subunit and inhibits protein synthesis, giving a bacteriostatic effect against susceptible organisms.

Prescribing in practice

  • Azithromycin prolongs the QT interval, so avoid combining with other QT-prolonging drugs and use caution where there is known cardiac conduction risk.
  • Dose by weight using a children's formulary, and be aware of an association with infantile hypertrophic pyloric stenosis when macrolides are used in very young infants.
  • Gastrointestinal upset is common, and macrolides interact with several drugs metabolised through hepatic enzymes.

Monitoring

Monitor clinical response, gastrointestinal tolerance, and consider cardiac risk where other QT-prolonging factors are present.

Counselling the patient

  • The course is usually short because the medicine stays in the body for some time.
  • Report vomiting, especially forceful vomiting in a young infant.
  • Tell the prescriber about any heart rhythm problems or other regular medicines.

Evidence & guidelines

Azithromycin features in UK guidance for pertussis and selected paediatric infections, with recognised QT-prolongation precautions.

Reference: PHE Antibiotic Guidelines; NICE NG138; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways