What is the appropriate azithromycin (Z‑Pack) dosing regimen for a child?

Azithromycin (Z-Pack) Dosing for Children

The standard pediatric azithromycin regimen 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, 3

Weight-Based Dosing Table

For practical administration, use these weight-band doses for the 5-day regimen: 1, 2

Weight	Day 1 Dose	Days 2–5 Dose	Total Course
15–25 kg (33–55 lbs)	200 mg	100 mg daily	600 mg
26–35 kg (57–77 lbs)	300 mg	150 mg daily	900 mg
36–45 kg (79–99 lbs)	400 mg	200 mg daily	1,200 mg
≥46 kg (≥101 lbs)	500 mg	250 mg daily	1,500 mg

Alternative 3-Day Regimen

For acute otitis media and acute bacterial sinusitis only, a simplified 3-day course of 10 mg/kg (maximum 500 mg) once daily may be used. 3, 4 This regimen has comparable efficacy to the 5-day course for these specific indications. 4

Single-Dose Regimen for Otitis Media

A single 30 mg/kg dose (maximum 1,200 mg) is FDA-approved for acute otitis media, though the 5-day regimen remains more commonly used. 3

Indication-Specific Guidance

Community-Acquired Pneumonia (≥6 months)

• Use the standard 5-day regimen (10 mg/kg day 1, then 5 mg/kg days 2–5). 1, 2
• Azithromycin is appropriate for atypical pathogens (Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia trachomatis). 1, 2
• Do NOT use azithromycin as first-line for typical bacterial pneumonia caused by Streptococcus pneumoniae or Haemophilus influenzae; amoxicillin 90 mg/kg/day is preferred. 1, 2

Streptococcal Pharyngitis/Tonsillitis

• Penicillin or amoxicillin remain first-line; azithromycin is second-line only. 1, 2
• If azithromycin is used, prescribe 12 mg/kg once daily for 5 days (maximum 500 mg/day) to reduce recurrence rates. 1, 2, 3
• The standard 10 mg/kg regimen has unacceptably high recurrence rates for strep throat. 1

Pertussis (≥6 months)

• Use the standard 5-day regimen (10 mg/kg day 1, then 5 mg/kg days 2–5). 1
• For infants <6 months, use 10 mg/kg once daily for 5 consecutive days. 1

Acute Otitis Media & Sinusitis

• Either the 5-day regimen OR the 3-day regimen (10 mg/kg daily × 3 days) is acceptable. 3, 4

Administration Considerations

• Azithromycin can be taken with or without food. 1, 2, 3
• Do NOT give simultaneously with aluminum- or magnesium-containing antacids; separate by at least 2 hours, as antacids reduce absorption by ~30%. 1, 2
• Oral suspension must be reconstituted with water before administration. 1

Expected Clinical Response

Children should show clinical improvement within 48–72 hours of starting therapy. 1, 2 If no improvement or clinical deterioration occurs within this window, reassess the diagnosis, consider resistant organisms or complications (e.g., parapneumonic effusion), and adjust therapy accordingly. 1, 2

Intravenous Dosing (Hospitalized Children)

For children unable to tolerate oral therapy, give 10 mg/kg IV once daily (maximum 500 mg) on days 1–2, then transition to oral as soon as feasible. 1, 2 Infuse at 1 mg/mL over 3 hours OR 2 mg/mL over 1 hour. 1

Special Populations

HIV-Infected Children (MAC Prophylaxis)

• 20 mg/kg once weekly (maximum 1,200 mg per dose) for Mycobacterium avium complex prophylaxis. 1, 2

Adolescents with Chlamydial Urethritis/Cervicitis

• Single 1-gram oral dose. 1

Common Pitfalls to Avoid

• Do NOT underdose the day 1 loading dose; the full 10 mg/kg is essential to achieve therapeutic tissue concentrations. 1, 2
• Do NOT use azithromycin as first-line for typical bacterial pneumonia or strep throat; β-lactams have superior outcomes. 1, 2
• Do NOT use the standard 10 mg/kg regimen for strep pharyngitis; it requires 12 mg/kg daily to prevent recurrence. 1, 2
• Do NOT continue IV therapy beyond 2 days when oral therapy is feasible. 1

Monitoring Requirements

• Short courses (3–5 days) require no routine laboratory or cardiac monitoring. 2
• For prolonged therapy (e.g., non-tuberculous mycobacterial infection): obtain baseline ECG, repeat at 2 weeks and after adding QT-prolonging drugs; perform baseline and intermittent audiometry; check liver function, renal function, and CBC intermittently. 1, 2

Safety Profile

• Most common adverse effects: diarrhea (5–6%), vomiting (2–6%), abdominal discomfort, nausea. 1, 2, 5
• Azithromycin causes significantly fewer GI side effects than erythromycin (diarrhea 2% vs 29%) and is better tolerated than amoxicillin/clavulanate. 1, 2, 5
• Discontinuation due to adverse events is rare (~1% of pediatric courses). 2
• No dosage adjustment needed for renal impairment (GFR ≥10 mL/min). 3