Azithromycin Dosing and Administration
Pediatric Dosing (≥6 months)
For respiratory tract infections caused by atypical pathogens (Mycoplasma pneumoniae, Chlamydia spp.), give 10 mg/kg (maximum 500 mg) on day 1, then 5 mg/kg (maximum 250 mg) once daily on days 2–5. This 5-day regimen is the standard recommendation from the Infectious Diseases Society of America and American Academy of Pediatrics. 1, 2
Weight-Band Dosing (Simplified Alternative)
For children 6 months to 17 years, the British Thoracic Society recommends once-daily dosing based on weight bands: 1, 2
- 15–25 kg: 200 mg once daily
- 26–35 kg: 300 mg once daily
- 36–45 kg: 400 mg once daily
- ≥46 kg: 500 mg once daily
Critical Indication-Specific Guidance
Atypical pneumonia (Mycoplasma, Chlamydia): Azithromycin is first-line therapy. 1, 2
Typical bacterial pneumonia (Streptococcus pneumoniae, Haemophilus influenzae): Do NOT use azithromycin as first-line—amoxicillin 90 mg/kg/day is superior and required. 1, 2
Streptococcal pharyngitis: Penicillin or amoxicillin remain first-line; if azithromycin is necessary (β-lactam allergy), use 12 mg/kg once daily for 5 days (maximum 500 mg/day) to reduce recurrence. 1, 2
Pertussis (≥6 months): 10 mg/kg (max 500 mg) day 1, then 5 mg/kg (max 250 mg) daily days 2–5. 1, 2, 3
Intravenous Dosing (Hospitalized Children)
Give 10 mg/kg IV once daily (maximum 500 mg) on days 1–2, then transition to oral therapy as soon as feasible. Infuse at 1 mg/mL over 3 hours OR 2 mg/mL over 1 hour. 1, 2
Special Populations
MAC prophylaxis in HIV-infected children: 20 mg/kg once weekly (maximum 1,200 mg per dose). 1, 2, 3
Chlamydial conjunctivitis in neonates: 20 mg/kg once daily for 3 days. 3
Adult Dosing
For community-acquired respiratory infections, give 500 mg once daily for 3 days OR 500 mg on day 1, then 250 mg once daily on days 2–5. The 3-day regimen provides equivalent efficacy due to azithromycin's prolonged tissue half-life (68 hours) and improves compliance. 3, 4
Indication-Specific Regimens
Uncomplicated chlamydial urethritis/cervicitis: Single 1 g oral dose—this is the CDC's definitive recommendation, enabling directly observed therapy and superior compliance. 3
Severe community-acquired pneumonia (hospitalized, non-ICU): 500 mg IV daily for 2–5 days, then oral 500 mg daily to complete 7–10 days total. 3
Bronchiectasis with ≥3 exacerbations/year: 500 mg three times weekly OR 250 mg daily for at least 6 months. 3
Cat scratch disease (>45 kg): 500 mg day 1, then 250 mg daily for 4 additional days. 3
Disseminated MAC in AIDS: 250 mg daily with ethambutol ± rifabutin. 3
MAC prophylaxis in AIDS (CD4 <50): 1,200 mg once weekly. 3
Legionella pneumonia: Extend treatment to 21 days. 3
Administration Considerations
Food: Azithromycin can be taken with or without meals. 1
Antacids: Separate aluminum- or magnesium-containing antacids by at least 2 hours—they reduce absorption by approximately 30%. 1, 2, 3
Oral suspension: Must be reconstituted with water before dosing. 2
Expected Clinical Response & Monitoring
Children and adults should show clinical improvement within 48–72 hours. If no improvement or deterioration occurs, reassess for complications, resistance, or alternative pathogens. 1, 2
Short Courses (3–5 days)
Routine laboratory or cardiac monitoring is not required. 1
Prolonged Therapy (e.g., bronchiectasis, NTM)
- Baseline ECG, repeat at 2 weeks and after adding any QT-prolonging drug 1, 2
- Baseline and intermittent audiometry 1
- Liver function, renal function, and CBC checked intermittently 1, 2
- Ensure at least one negative NTM culture before starting long-term macrolides 3
Safety Profile & Contraindications
Common Adverse Effects
Diarrhea (5–6%), vomiting (2–6%), abdominal discomfort, nausea, headache, and dizziness. 1, 3 Azithromycin causes significantly fewer gastrointestinal events than erythromycin (≈2% vs 29%). 1
QT Prolongation Risk
Obtain baseline ECG in patients with:
- Cardiovascular disease
- Concurrent QT-prolonging medications
- QTc >450 ms (men) or >470 ms (women)—contraindication 3
Avoid azithromycin in patients taking amiodarone, Class IA/III antiarrhythmics, certain antipsychotics, or fluoroquinolones without cardiology consultation. 3
Drug Interactions
- Minimal cytochrome P450 interactions—strongly preferred over clarithromycin in elderly patients. 3
- Monitor potassium when combined with trimethoprim-sulfamethoxazole and ACE-inhibitors/ARBs. 3
Renal & Hepatic Impairment
- Renal impairment: Use caution in severe impairment (CrCl <10 mL/min); AUC increases 35%, Cmax increases 61%. 3
- Hepatic impairment: Use caution and increase monitoring; biliary excretion is the main elimination route. 3, 5
Critical Pitfalls to Avoid
Do NOT underdose day 1—the 10 mg/kg loading dose is essential to achieve therapeutic tissue concentrations. 1
Do NOT use azithromycin as first-line for typical bacterial pneumonia or strep throat—β-lactams have superior outcomes. 1, 2
Do NOT use azithromycin as monotherapy for gonorrhea—widespread resistance mandates combination with ceftriaxone. 3
Do NOT prolong IV therapy beyond 2 days when oral therapy is feasible. 2
Do NOT ignore cardiovascular risk—Tennessee Medicaid data showed increased cardiovascular deaths (HR 2.88) with azithromycin, especially in high-risk patients. 3