Antibiotic — Macrolide

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.

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.

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.

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. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways