Azithromycin Dosing for a 5-Year-Old Weighing 42 Pounds
For a 5-year-old child weighing 42 pounds (19 kg), the recommended dose of liquid azithromycin depends on the specific infection being treated, but for most common respiratory infections (community-acquired pneumonia, acute otitis media, acute bacterial sinusitis), give 10 mg/kg (approximately 190 mg or 9.5 mL of 100 mg/5 mL suspension, or 4.75 mL of 200 mg/5 mL suspension) on day 1, followed by 5 mg/kg (approximately 95 mg or 4.75 mL of 100 mg/5 mL suspension, or 2.4 mL of 200 mg/5 mL suspension) once daily on days 2 through 5. 1
Weight-Based Dosing Calculation
Your patient weighs 42 pounds, which converts to approximately 19 kg. Based on FDA-approved dosing tables: 1
For the standard 5-day regimen (community-acquired pneumonia, acute otitis media):
- Day 1: 5 mL of 200 mg/5 mL suspension (or 10 mL of 100 mg/5 mL suspension) = 200 mg
- Days 2-5: 2.5 mL of 200 mg/5 mL suspension (or 5 mL of 100 mg/5 mL suspension) = 100 mg daily 1
Alternative 3-day regimen (acute otitis media, acute bacterial sinusitis):
- 5 mL of 200 mg/5 mL suspension (or 10 mL of 100 mg/5 mL suspension) = 200 mg once daily for 3 days 1
Indication-Specific Considerations
The dosing varies significantly based on the diagnosis:
Community-acquired pneumonia (atypical pathogens): Use the 5-day regimen with 10 mg/kg day 1, then 5 mg/kg days 2-5, as this is specifically recommended by the Infectious Diseases Society of America and American Academy of Pediatrics for Mycoplasma pneumoniae, Chlamydia pneumoniae, or Chlamydia trachomatis 2, 3
Streptococcal pharyngitis/tonsillitis: This requires a higher dose of 12 mg/kg once daily for 5 days (approximately 228 mg or 5.7 mL of 200 mg/5 mL suspension daily) because the standard 10 mg/kg regimen has high recurrence rates 2, 4. However, penicillin or amoxicillin remains first-line therapy, and azithromycin should only be used as second-line 2, 3
Acute otitis media: Can use either the 5-day regimen, 3-day regimen (10 mg/kg daily), or single 30 mg/kg dose (approximately 570 mg or 14.25 mL of 200 mg/5 mL suspension) 1
Critical Pitfalls to Avoid
Do not use azithromycin as first-line for typical bacterial pneumonia caused by S. pneumoniae or H. influenzae—beta-lactam antibiotics (amoxicillin, amoxicillin-clavulanate) remain first-line for these typical pathogens 2, 3
Avoid concurrent administration with aluminum- or magnesium-containing antacids, as they reduce azithromycin absorption 2, 3
For strep throat, recognize that azithromycin is second-line only and requires the higher 12 mg/kg dose to prevent treatment failures 2, 4
Monitor for QT prolongation when used with other QT-prolonging medications 2, 3
Administration Details
Azithromycin suspension can be taken with or without food 1
The medication is generally well-tolerated, with gastrointestinal side effects (abdominal discomfort, diarrhea, nausea, vomiting) being the most common but typically mild to moderate 2, 5
Both 3-day and 5-day regimens have comparable efficacy and tolerability for respiratory infections in children 6