Azithromycin

Macrolide·Infectious Diseases - Macrolides

Atypical pneumonia (Legionella, Mycoplasma), Chlamydia, Pertussis, severe Campylobacter

PBSMACROLIDEZithromax500 mg tabletS4+1

Max Dose

500 mg/day

Half-life

68 h

QTc Risk

HIGH

CYP3A4

WEAK

Rapid Summary

Overview

Unique macrolide that rapidly leaves the blood and concentrates massively inside phagocytes and tissues. Delivers localized therapy for days after the last dose.

Maximum Dose

Max 500 mg/day (or 1g single STAT dose for STIs).

Clinical Focus

Known to prolong the QTc interval. However, it lacks the severe CYP3A4 drug interactions seen with Clarithromycin.

Bottom Line

Azithromycin is a convenient 3-5 day macrolide for atypical pneumonia, STIs, and penicillin-allergic patients, but prolongs QTc and has significant drug interactions via CYP3A4.

Formulation & Access

Brand Names

Zithromax

Oral Routes

Tablets (500 mg). Oral liquid.

Parenteral

Ampoule (500 mg) for IV use.

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Atypical pneumonia (Legionella, Mycoplasma), Chlamydia, Pertussis, severe Campylobacter.

Off-Label

OFF

Prokinetic for severe gastroparesis (IV). Chronic inflammation reduction in COPD.

Clinical Place

First-line empirical addition to Ceftriaxone for severe CAP to cover 'atypicals'.

Quick reference

Class & Role

Macrolide — Unique macrolide that rapidly leaves the blood and concentrates massively inside phagocytes and tissues.

Route / Formulation

Tablets (500 mg). Oral liquid. (Zithromax)

Usual Dose & Max

PO / IV 500 mg OD for 3 days. Max 500 mg/day (or 1g single STAT dose for STIs).

Key Indication Doses

Community Acquired Pneumonia: PO / IV 500 mg OD for 3 days. Chlamydia Trachomatis: PO 1 g STAT. COPD Exacerbation Prophylaxis: PO 250 mg 3 times a week (Specialist off-label).

Best Uses

Azithromycin is a convenient 3-5 day macrolide for atypical pneumonia, STIs, and penicillin-allergic patients, but prolongs QTc and has significant drug interactions via CYP3A4.

Avoid / Cautions

Baseline QTc > 500 ms, history of macrolide-induced cholestatic jaundice. Pregnancy Category B1. The safest macrolide in pregnancy.

Key Risks

Cardiovascular: QTc prolongation, potentially leading to Torsades de Pointes/VF. Gastrointestinal: Nausea, severe abdominal cramping, diarrhea (due to motilin receptor agonism). Otic: Reversible hearing loss (with prolonged high-dose use).

Key Interactions

Unlike Clarithromycin and Erythromycin, Azithromycin does NOT significantly inhibit CYP3A4. It is much safer to use alongside statins and DOACs. Additive QTc prolongation with Amiodarone, Haloperidol, Sotalol, Ondansetron.

Monitoring

Baseline ECG before giving IV or prescribing to elderly patients on multiple cardiac meds. Check U&E to ensure potassium and magnesium are normal to prevent arrhythmias.

Clinical Pearl

Because it binds to motilin receptors in the gut, IV Azithromycin (250mg) is sometimes used in the ICU as a highly potent prokinetic to force gastric emptying when a patient's bowels have completely stalled.

Access

Zithromax500 mg tablet

Brand: Zithromax
Formulation: Tablets (500 mg)

Azithromycin

Macrolide·Infectious Diseases - Macrolides

Atypical pneumonia (Legionella, Mycoplasma), Chlamydia, Pertussis, severe Campylobacter

PBSMACROLIDEZithromax500 mg tabletS4+1

Max Dose

500 mg/day

Half-life

68 h

QTc Risk

HIGH

CYP3A4

WEAK

Rapid Summary

Overview

Unique macrolide that rapidly leaves the blood and concentrates massively inside phagocytes and tissues. Delivers localized therapy for days after the last dose.

Maximum Dose

Max 500 mg/day (or 1g single STAT dose for STIs).

Clinical Focus

Known to prolong the QTc interval. However, it lacks the severe CYP3A4 drug interactions seen with Clarithromycin.

Bottom Line

Azithromycin is a convenient 3-5 day macrolide for atypical pneumonia, STIs, and penicillin-allergic patients, but prolongs QTc and has significant drug interactions via CYP3A4.

Formulation & Access

Brand Names

Zithromax

Oral Routes

Tablets (500 mg). Oral liquid.

Parenteral

Ampoule (500 mg) for IV use.

Prescribing & PBS

Unrestricted General Benefit (S4).

Indications & Use

Primary

PBSTGA

Atypical pneumonia (Legionella, Mycoplasma), Chlamydia, Pertussis, severe Campylobacter.

Off-Label

OFF

Prokinetic for severe gastroparesis (IV). Chronic inflammation reduction in COPD.

Clinical Place

First-line empirical addition to Ceftriaxone for severe CAP to cover 'atypicals'.

Quick reference

Class & Role

Macrolide — Unique macrolide that rapidly leaves the blood and concentrates massively inside phagocytes and tissues.

Route / Formulation

Tablets (500 mg). Oral liquid. (Zithromax)

Usual Dose & Max

PO / IV 500 mg OD for 3 days. Max 500 mg/day (or 1g single STAT dose for STIs).

Key Indication Doses

Community Acquired Pneumonia: PO / IV 500 mg OD for 3 days. Chlamydia Trachomatis: PO 1 g STAT. COPD Exacerbation Prophylaxis: PO 250 mg 3 times a week (Specialist off-label).

Best Uses

Azithromycin is a convenient 3-5 day macrolide for atypical pneumonia, STIs, and penicillin-allergic patients, but prolongs QTc and has significant drug interactions via CYP3A4.

Avoid / Cautions

Baseline QTc > 500 ms, history of macrolide-induced cholestatic jaundice. Pregnancy Category B1. The safest macrolide in pregnancy.

Key Risks

Key Interactions

Monitoring

Baseline ECG before giving IV or prescribing to elderly patients on multiple cardiac meds. Check U&E to ensure potassium and magnesium are normal to prevent arrhythmias.

Clinical Pearl

Access

Zithromax500 mg tablet

Brand: Zithromax
Formulation: Tablets (500 mg)