What is the correct weight‑based dosing schedule for azithromycin in children, including maximum daily caps and dosing variations for specific infections?

Azithromycin Pediatric Dosing

The standard pediatric dose of azithromycin 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 most respiratory tract infections in children ≥6 months of age. 1, 2, 3

Standard Weight-Based Dosing by Indication

Community-Acquired Pneumonia (Atypical Pathogens)

• 10 mg/kg (max 500 mg) on day 1, then 5 mg/kg (max 250 mg) daily for days 2–5 1, 2, 3
• This 5-day regimen is specifically indicated for atypical pathogens (Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia trachomatis) 1, 2
• Critical caveat: Azithromycin should NOT be used as first-line therapy for typical bacterial pneumonia caused by S. pneumoniae or H. influenzae—amoxicillin at 90 mg/kg/day remains first-line 1, 2

Acute Otitis Media

The FDA label provides three alternative regimens 3:

• 5-day regimen: 10 mg/kg day 1, then 5 mg/kg days 2–5 3
• 3-day regimen: 10 mg/kg once daily for 3 days 3
• Single-dose regimen: 30 mg/kg as a single dose 3

Acute Bacterial Sinusitis

• 10 mg/kg once daily for 3 days 3
• The FDA notes that effectiveness of the 5-day or 1-day regimen has not been established for sinusitis 3

Pharyngitis/Tonsillitis (Second-Line Only)

• 12 mg/kg once daily for 5 days (maximum 500 mg/day) 1, 3
• This higher dose (12 mg/kg vs. 10 mg/kg) is essential because standard 10 mg/kg dosing results in high recurrence rates for streptococcal pharyngitis 1
• Penicillin or amoxicillin remains first-line; azithromycin is reserved for penicillin allergy 1, 2

Pertussis (Treatment and Prophylaxis)

• Infants <1 month: 10 mg/kg once daily for 5 days 1
• Infants 1–5 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

Genital Chlamydial Infections (Adolescents)

• Single 1-gram oral dose 1

MAC Prophylaxis (HIV-Infected Children)

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

Age-Specific Considerations

Infants <6 Months

• Azithromycin is the preferred macrolide for pertussis in this age group 1, 2
• For infants <1 month, azithromycin has not been associated with infantile hypertrophic pyloric stenosis (IHPS), though monitoring is recommended 1

Children ≥6 Months

• Standard 5-day regimen is appropriate for most indications 1, 2, 3

Adolescents

• Use adult maximum doses (500 mg day 1,250 mg days 2–5) regardless of weight 1

Weight-Band Dosing (British Thoracic Society Alternative)

For chronic therapy or when precise weight-based calculation is impractical 1:

• 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

Intravenous Dosing

• 10 mg/kg IV once daily (maximum 500 mg) on days 1–2 only 1
• Transition to oral therapy as soon as clinically feasible 1, 2
• IV azithromycin is specifically indicated for atypical pathogens when parenteral therapy is required 1
• Common pitfall: Do not continue IV therapy beyond 2 days when oral therapy is feasible 1, 2

Administration Guidelines

Timing and Food

• Azithromycin can be taken with or without food 1, 3
• Oral suspension should be administered 1 hour before or 2 hours after meals for optimal absorption 1

Drug Interactions

• Do NOT administer simultaneously with aluminum- or magnesium-containing antacids—separate by at least 2 hours, as antacids reduce absorption 1, 2
• Monitor for QT prolongation when used with other QT-prolonging medications 1, 2

Monitoring for Prolonged Courses

• Baseline ECG, repeat at 2 weeks, and after adding any QT-prolonging medication 1
• Baseline and intermittent audiometry during prolonged treatment 1
• Periodic liver function tests, renal function, and complete blood count 1

Expected Clinical Response

• Children should show 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, and adjust therapy accordingly 1

Critical Pitfalls to Avoid

1. Do not underdose the initial 10 mg/kg dose on day 1—full dosing is essential to achieve therapeutic tissue levels 1

2. Do not use azithromycin as first-line for typical bacterial pneumonia or streptococcal pharyngitis—β-lactam agents have superior outcomes and lower recurrence rates 1, 2

3. Do not use the standard 10 mg/kg regimen for strep throat—the higher 12 mg/kg dose for 5 days is required to prevent recurrence 1, 4

4. Do not prolong IV therapy beyond 2 days when oral therapy is feasible 1, 2

5. Do not administer with antacids—separate by at least 2 hours 1, 2

Safety Profile

• Azithromycin has fewer gastrointestinal side effects than erythromycin 1, 2
• Common adverse effects include abdominal discomfort, diarrhea, nausea, vomiting, headache, and dizziness 1
• Rare but serious adverse effects include acute interstitial nephritis, allergic reactions/anaphylaxis, and pseudomembranous colitis 1
• FDA Pregnancy Category B 1

Renal and Hepatic Impairment

• No dosage adjustment required for renal impairment (GFR ≥10 mL/min) 3
• Use caution in severe renal impairment (GFR <10 mL/min), as AUC increases 35% 3
• No specific dosage adjustment recommendations for hepatic impairment, but use caution as azithromycin undergoes primarily biliary excretion 1, 3