What is the appropriate dose of azithromycin (Zithromax) 200 mg/5 mL suspension for a 63‑lb (≈28.5 kg) child?

Azithromycin Dosing for a 63-lb (28.5-kg) Child

For a 63-lb (28.5-kg) child, administer 7.5 mL of azithromycin 200 mg/5 mL suspension once daily on day 1, followed by 3.75 mL once daily on days 2–5, for the standard 5-day respiratory infection regimen. 1, 2

Weight-Based Dose Calculation

• A 63-lb child weighs approximately 28.5 kg, which falls into the 26–35 kg weight band recommended by the British Thoracic Society. 1
• For the standard 5-day regimen (community-acquired pneumonia, atypical pneumonia), the dose is 10 mg/kg on day 1 (maximum 500 mg), followed by 5 mg/kg once daily on days 2–5 (maximum 250 mg per day). 1, 2
• Day 1 dose: 28.5 kg × 10 mg/kg = 285 mg = 7.5 mL of the 200 mg/5 mL suspension (rounded to nearest practical volume). 1, 2
• Days 2–5 dose: 28.5 kg × 5 mg/kg = 142.5 mg = 3.75 mL (¾ teaspoon) of the 200 mg/5 mL suspension once daily. 1, 2

Indication-Specific Considerations

Community-Acquired Pneumonia & Atypical Pathogens

• The 5-day regimen (10 mg/kg day 1, then 5 mg/kg days 2–5) is the preferred schedule for atypical pneumonia caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, or Chlamydia trachomatis in children ≥6 months. 1, 2
• Azithromycin should not be used as first-line monotherapy for typical bacterial pneumonia caused by Streptococcus pneumoniae or Haemophilus influenzae; amoxicillin 90 mg/kg/day remains the preferred agent for those pathogens. 1

Acute Otitis Media

• For acute otitis media, the FDA label offers three regimens: 30 mg/kg as a single dose (1-day), 10 mg/kg once daily for 3 days, or the standard 5-day regimen. 2
• For a 28.5-kg child, the 1-day regimen would be 22.5 mL of the 200 mg/5 mL suspension (855 mg total). 2

Streptococcal Pharyngitis

• For strep throat, azithromycin is second-line only (penicillin or amoxicillin remain first-line), and requires a higher dose of 12 mg/kg once daily for 5 days (maximum 500 mg/day) due to higher recurrence rates with the standard 10 mg/kg regimen. 1, 2
• For a 28.5-kg child with pharyngitis, the dose would be 342 mg = 8.5 mL of the 200 mg/5 mL suspension once daily for 5 days. 1, 2

Administration & Safety

• Azithromycin can be taken with or without food, but must not be given simultaneously with aluminum- or magnesium-containing antacids; separate administration by at least 2 hours to avoid reduced absorption. 1, 2
• Common adverse effects include gastrointestinal disturbances (abdominal discomfort, diarrhea, nausea, vomiting), dizziness, and headache; these are generally milder than with erythromycin. 1, 3, 4
• For prolonged courses (e.g., non-tuberculous mycobacterial infection), obtain baseline ECG and repeat at 2 weeks because azithromycin can prolong the QT interval. 1

Expected Clinical Response & Monitoring

• Children on appropriate azithromycin therapy 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 (including typical bacteria requiring β-lactam therapy), evaluate for complications (e.g., parapneumonic effusion), and adjust therapy accordingly. 1

Common Pitfalls to Avoid

• Do not underdose the initial 10 mg/kg dose on day 1; full dosing is essential to achieve therapeutic tissue levels. 1
• Do not prescribe azithromycin as first-line for typical bacterial pneumonia or streptococcal pharyngitis, as β-lactam agents have superior outcomes and lower recurrence rates. 1
• 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, 2