Amoxicillin Dosing for Strep Throat in a 2-Year-Old (33 lb/15 kg)
Give amoxicillin 50 mg/kg once daily (750 mg once daily) OR 25 mg/kg twice daily (375 mg twice daily) for 10 days.
Recommended Dosing Regimen
For this 15 kg child with streptococcal pharyngitis, the FDA-approved dosing and IDSA guidelines support the following options 1, 2:
- Once-daily dosing: 50 mg/kg/day = 750 mg once daily (maximum 1000 mg)
- Twice-daily dosing: 25 mg/kg twice daily = 375 mg twice daily (total 750 mg/day)
Duration: 10 days is mandatory to prevent acute rheumatic fever 1, 2.
Key Dosing Principles
The IDSA guideline for streptococcal pharyngitis explicitly recommends amoxicillin at 50 mg/kg once daily (max 1000 mg) or 25 mg/kg twice daily (max 500 mg per dose) for 10 days 1. This is the preferred first-line therapy over penicillin V due to better palatability and equivalent efficacy.
The FDA label confirms these dosing parameters for ear/nose/throat infections in children ≥3 months and <40 kg, specifying mild/moderate infections use 25 mg/kg/day divided every 12 hours or 20 mg/kg/day divided every 8 hours 2. However, for streptococcal pharyngitis specifically, the higher once-daily dosing (50 mg/kg) is supported by both guideline and research evidence 1, 3.
Evidence Supporting Once-Daily Dosing
Recent research demonstrates that once-daily amoxicillin (40-50 mg/kg/day) achieves equivalent bacterial eradication compared to multiple daily doses 3. In a PCR-based study, the once-daily regimen showed 85.7% negative results at follow-up, comparable to twice-daily (72.7%) and three-times-daily (85.7%) regimens, with no statistical differences in bacterial load reduction 3.
Practical Administration
- Give with food to minimize gastrointestinal side effects 2
- For a 15 kg child receiving 750 mg once daily, use oral suspension (typically 250 mg/5 mL concentration = 15 mL once daily)
- Alternatively, 375 mg twice daily = 7.5 mL of 250 mg/5 mL suspension twice daily
- Complete the full 10-day course even if symptoms resolve earlier 1, 2
Critical Pitfalls to Avoid
Do not shorten the duration below 10 days for streptococcal pharyngitis. While some research suggests 5-7 day courses may be effective 4, the IDSA guideline and FDA label are unequivocal that 10 days is required to prevent acute rheumatic fever 1, 2. This is non-negotiable for Group A streptococcal infections.
Do not underdose larger children or overdose smaller children. Research shows a concerning trend where older/heavier children receive inadequate mg/kg dosing as clinicians approach "adult maximum doses" prematurely 5. For this 15 kg child, ensure the full 50 mg/kg/day is prescribed.
Alternative for Penicillin Allergy
If the child has a non-anaphylactic penicillin allergy, first-generation cephalosporins are appropriate 1:
- Cephalexin 20 mg/kg twice daily (300 mg twice daily) for 10 days
- Cefadroxil 30 mg/kg once daily (450 mg once daily) for 10 days
For anaphylactic penicillin allergy, use 1:
- Azithromycin 12 mg/kg once daily (180 mg once daily, max 500 mg) for 5 days
- Clindamycin 7 mg/kg three times daily (105 mg three times daily, max 300 mg/dose) for 10 days
Note that macrolide resistance varies geographically and is increasing in some U.S. regions 1, 6.