What is the recommended azithromycin (Zithromax) dosing for children, including weight-based doses, maximum limits, and regimen duration for common infections?

Azithromycin (Zithromax) Pediatric Dosing

The standard azithromycin regimen for children is 10 mg/kg (maximum 500 mg) on day 1, followed by 5 mg/kg (maximum 250 mg) once daily on days 2–5, for a total 5-day course. 1, 2

Standard Weight-Based Dosing

For children ≥6 months with respiratory tract infections:

• Day 1: 10 mg/kg (maximum 500 mg) as a single dose 1, 2
• Days 2–5: 5 mg/kg (maximum 250 mg) once daily 1, 2

Simplified weight-band dosing (British Thoracic Society):

Weight	Daily Dose
15–25 kg	200 mg once daily [1]
26–35 kg	300 mg once daily [1]
36–45 kg	400 mg once daily [1]
≥46 kg	500 mg once daily [1]

This weight-band approach simplifies dosing while maintaining therapeutic efficacy for the standard 5-day course. 1

Age-Specific Considerations

Infants <1 month (pertussis treatment/prophylaxis):

• 10 mg/kg once daily for 5 days 1, 2
• Azithromycin is the preferred macrolide in this age group due to superior safety profile compared to erythromycin 1
• Monitor for infantile hypertrophic pyloric stenosis (IHPS), though azithromycin has not been strongly associated with this complication 1

Infants 1–5 months (pertussis):

• Same dosing: 10 mg/kg once daily for 5 days 1

Children ≥6 months:

• Standard 5-day regimen as outlined above 1, 2

Indication-Specific Dosing

Community-Acquired Pneumonia (Atypical Pathogens)

Azithromycin is indicated specifically for atypical pathogens (Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia trachomatis), not as first-line for typical bacterial pneumonia. 1, 2

• Oral: 10 mg/kg (max 500 mg) day 1, then 5 mg/kg (max 250 mg) days 2–5 1, 2
• IV (when parenteral therapy required): 10 mg/kg once daily (max 500 mg) on days 1–2, then transition to oral therapy as soon as clinically feasible 1

Critical caveat: For typical bacterial pneumonia caused by Streptococcus pneumoniae or Haemophilus influenzae, amoxicillin 90 mg/kg/day remains first-line; azithromycin should not be used as monotherapy. 1, 2

Streptococcal Pharyngitis

Azithromycin is second-line only—penicillin or amoxicillin remain first-line. 1

• Higher dose required: 12 mg/kg once daily for 5 days (maximum 500 mg/day) 1
• The standard 10 mg/kg regimen has unacceptably high recurrence rates for strep throat 1

Acute Otitis Media

• Standard 5-day regimen: 10 mg/kg day 1, then 5 mg/kg days 2–5 2
• Alternative 3-day regimen: 10 mg/kg once daily for 3 days 3, 4

Pertussis (Treatment and Post-Exposure Prophylaxis)

• Infants <6 months: 10 mg/kg once daily for 5 days 1
• Children ≥6 months: 10 mg/kg (max 500 mg) day 1, then 5 mg/kg (max 250 mg) days 2–5 1

Mycobacterium Avium Complex (MAC) Prophylaxis in HIV

• 20 mg/kg once weekly (maximum 1,200 mg per dose) 1

Uncomplicated Chlamydial Infections (Adolescents)

• Single 1-gram oral dose 1

Intravenous Administration

When parenteral therapy is required (e.g., hospitalized child unable to tolerate oral):

• 10 mg/kg once daily (maximum 500 mg) on days 1–2 1
• Infusion rate: 1 mg/mL over 3 hours OR 2 mg/mL over 1 hour 1
• Transition to oral therapy as soon as the patient can tolerate it—do not prolong IV therapy beyond 2 days when oral is feasible 1, 2

Administration Guidelines

Timing with food:

• Azithromycin can be taken with or without food 1
• Some sources recommend 1 hour before or 2 hours after meals for optimal absorption 1

Antacid interactions:

• Do not administer simultaneously with aluminum- or magnesium-containing antacids—separate by at least 2 hours, as antacids reduce drug absorption 1, 2

Oral suspension:

• Reconstitute with water before administration 1
• Preferred formulation for children who cannot swallow tablets 1

Expected Clinical Response

Children on appropriate azithromycin therapy should demonstrate clinical improvement within 48–72 hours. 1

• If no improvement or clinical deterioration occurs within this window, reassess the diagnosis, consider alternative pathogens, resistance patterns, or complications (e.g., parapneumonic effusion), and adjust therapy accordingly 1, 5

Critical Pitfalls to Avoid

Do not underdose the initial day 1 loading dose:

• The full 10 mg/kg on day 1 is essential to achieve therapeutic tissue levels 1

Do not use azithromycin as first-line for typical bacterial pneumonia or strep throat:

• β-lactam agents (amoxicillin) have superior outcomes and lower recurrence rates 1, 2

Do not prolong IV therapy unnecessarily:

• Limit IV azithromycin to days 1–2 only, then switch to oral 1, 2

Do not use standard dosing for strep throat:

• Requires higher dose (12 mg/kg daily) to prevent recurrence 1

Safety and Monitoring

Common adverse effects:

• Gastrointestinal disturbances (abdominal discomfort, diarrhea, nausea, vomiting), dizziness, headache 1
• Azithromycin has significantly fewer GI side effects than erythromycin 1, 2

QT prolongation:

• Monitor ECG at baseline, at 2 weeks, and after adding any QT-prolonging medications, especially with prolonged courses 1, 2

Drug interactions:

• Monitor when used with drugs metabolized by cytochrome P450 1

Laboratory monitoring (for prolonged courses):

• Baseline and intermittent audiometry 1
• Liver function tests, renal function, complete blood count checked sporadically 1

Hepatic impairment:

• Use caution—azithromycin undergoes primarily biliary excretion (only ~6% appears unchanged in urine) 1

Alternative Macrolides (If Azithromycin Contraindicated)

For children allergic to azithromycin:

• Clarithromycin: 15 mg/kg/day divided into 2 doses 1, 5
• Erythromycin: 40 mg/kg/day divided into 4 doses 1, 5
• Doxycycline: Only for children >7 years old (dental staining concerns) 1, 5

Clarithromycin may be preferred over erythromycin due to better tolerability and twice-daily dosing. 5