Azithromycin Dosing for a 40 lb Toddler
For a 40 lb (18 kg) toddler, administer azithromycin 10 mg/kg (180 mg) on day 1, followed by 5 mg/kg (90 mg) once daily on days 2-5, which translates to 9 mL of the 200 mg/5 mL suspension on day 1, then 4.5 mL daily for days 2-5. 1
Weight-Based Dosing Calculation
A 40 lb child weighs approximately 18 kg, falling into the standard pediatric dosing range:
- Day 1: 10 mg/kg = 180 mg (9 mL of 200 mg/5 mL suspension)
- Days 2-5: 5 mg/kg = 90 mg (4.5 mL of 200 mg/5 mL suspension) 1
This 5-day regimen is the preferred standard for community-acquired pneumonia and atypical pneumonia (Mycoplasma, Chlamydia) in children. 2, 3
Indication-Specific Considerations
For Community-Acquired Pneumonia or Atypical Pneumonia
The 5-day regimen (10 mg/kg day 1, then 5 mg/kg days 2-5) is the guideline-recommended approach for children ≥6 months with presumed atypical pneumonia caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, or Chlamydia trachomatis. 2
For Pharyngitis/Tonsillitis
If treating streptococcal pharyngitis, use 12 mg/kg once daily for 5 days (216 mg = 10.8 mL daily for 5 days) to prevent treatment failure and recurrence. 1 The higher dose is necessary because standard dosing has shown higher recurrence rates compared to penicillin. 4
For Acute Otitis Media
Alternative regimens exist but are less commonly used:
However, the 5-day regimen remains the most widely validated approach. 5
Administration Guidelines
- Can be taken with or without food 1
- Use the 200 mg/5 mL suspension strength for easier dosing in this weight range 1
- Ensure accurate measurement using calibrated oral syringes or dosing cups 1
Important Clinical Pearls
Avoid concurrent antacids: Do not administer azithromycin simultaneously with aluminum- or magnesium-containing antacids, as they significantly reduce absorption. 3 Separate administration by at least 2 hours.
Monitor for gastrointestinal effects: Approximately 9% of pediatric patients experience treatment-related adverse events, primarily mild-to-moderate gastrointestinal complaints (abdominal discomfort, diarrhea, nausea). 6 These rarely necessitate treatment discontinuation.
QT prolongation risk: Although rare in children, monitor for potential cardiac effects, especially if the child is on other QT-prolonging medications. 3
Re-dosing after vomiting: If the child vomits within 30 minutes of the first dose, re-dosing at the same total dose is reasonable, though safety data are limited. 1
Tissue Penetration and Duration
Azithromycin achieves sustained tissue concentrations that exceed MICs for common respiratory pathogens for days after the final dose, with an elimination half-life of approximately 31.6 hours in children. 7, 8 This extended tissue persistence supports the short 5-day treatment course while maintaining therapeutic efficacy.