Azithromycin Dosing for 9-Month-Old, 10 kg Infant
For a 9-month-old infant weighing 10 kg, administer azithromycin 100 mg (10 mg/kg) once daily on day 1, followed by 50 mg (5 mg/kg) once daily on days 2-5, for a total 5-day course.
Dosing Rationale
The FDA-approved dosing for infants aged 6 months and above follows a weight-based regimen 1:
- Day 1: 10 mg/kg = 100 mg (using 5 mL of 200 mg/5 mL suspension OR 2.5 mL of 100 mg/5 mL suspension)
- Days 2-5: 5 mg/kg/day = 50 mg (using 2.5 mL of 100 mg/5 mL suspension OR 1.25 mL of 200 mg/5 mL suspension)
- Total course: 300 mg over 5 days
This dosing applies to common pediatric infections including community-acquired pneumonia, acute otitis media, and atypical pneumonia caused by Mycoplasma pneumoniae or Chlamydia species 2.
Alternative Regimens by Indication
For Acute Otitis Media or Acute Bacterial Sinusitis:
- 3-day regimen: 10 mg/kg once daily for 3 days (100 mg daily × 3 days = 300 mg total) 1
- Single-dose regimen (otitis media only): 30 mg/kg as single dose (300 mg) 1
For Pertussis (if applicable):
- Infants <6 months: 10 mg/kg/day for 5 days 3
- This is the preferred macrolide for infants <1 month due to lower risk of infantile hypertrophic pyloric stenosis compared to erythromycin 3
Clinical Considerations
The 5-day regimen (10 mg/kg day 1, then 5 mg/kg days 2-5) is the most widely validated and recommended dosing schedule for pediatric respiratory infections 2. This regimen:
- Achieves therapeutic tissue concentrations that persist due to azithromycin's long half-life (68 hours) and extensive tissue distribution 1
- Has demonstrated safety and efficacy in multiple pediatric studies 4, 5, 6
- Minimizes antibiotic exposure while maintaining effectiveness 2
Important Caveats:
- Can be given with or without food 1
- Monitor for vomiting: If the infant vomits within 30 minutes of dosing, re-dosing at the same dose is acceptable based on clinical trial experience 1
- Adverse effects are uncommon (8.7% in pediatric studies), primarily mild gastrointestinal symptoms 5
- No dose adjustment needed for this age and weight 1
Formulation Selection:
For a 10 kg infant, the 100 mg/5 mL suspension provides easier dosing:
- Day 1: 5 mL (1 teaspoon)
- Days 2-5: 2.5 mL (½ teaspoon) daily
Alternatively, the 200 mg/5 mL suspension can be used but requires smaller volumes that may be harder to measure accurately in infants.