Amoxicillin Dosing for Streptococcal Pharyngitis in Children
For children with strep throat, amoxicillin should be dosed at 50 mg/kg once daily (maximum 1000 mg) or alternatively 25 mg/kg twice daily (maximum 500 mg per dose) for a full 10 days. 1, 2
Weight-Based Dosing Algorithm
For children weighing less than 40 kg:
- Preferred: 50 mg/kg once daily (maximum 1000 mg) for 10 days 1, 2
- Alternative: 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1, 2
For children weighing 40 kg or more (adolescents):
Critical Treatment Principles
Duration is non-negotiable: A complete 10-day course must be administered even if symptoms resolve earlier, as this is essential to prevent acute rheumatic fever 1, 2, 4. This represents a "strong, high" quality recommendation from the Infectious Diseases Society of America 1.
Timing of administration: Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 4.
Contagiousness: Children become non-contagious after 24 hours of antibiotic therapy 2, 3.
Evidence Supporting Once-Daily Dosing
The once-daily regimen is supported by high-quality evidence demonstrating non-inferiority to multiple daily dosing:
A large randomized controlled trial of 652 children showed once-daily amoxicillin (750 mg for <40 kg or 1000 mg for ≥40 kg) had comparable bacteriologic failure rates to twice-daily dosing, with no significant difference in adverse events 5.
Real-time PCR analysis confirmed that once-daily dosing achieves equivalent bacterial eradication compared to twice-daily or three-times-daily regimens 6.
The American Heart Association has endorsed once-daily amoxicillin dosing for streptococcal pharyngitis 2.
Why Higher Doses Are Recommended
The 50 mg/kg/day dosing (rather than older 40 mg/kg/day recommendations) is critical for several reasons:
A comparative study demonstrated that amoxicillin 40 mg/kg/day achieved significantly better clinical cure (87.9% vs 70.9%) and bacteriologic cure (79.3% vs 54.5%) compared to standard-dose penicillin V 7.
The carrier rate was substantially lower with amoxicillin (10.3% vs 23.6%) 7.
This higher dosing is particularly important given concerns about declining penicillin effectiveness, which may be due to inadequate dosing rather than true resistance 7.
Advantages of Amoxicillin Over Penicillin V
Amoxicillin is preferred as first-line therapy because:
- It has a narrow spectrum of activity with few adverse effects 2
- It demonstrates superior bacteriologic efficacy compared to penicillin V 7
- Once-daily dosing may improve adherence 2
- It remains highly effective with proven safety and low cost 1, 2
Alternative Regimens for Penicillin Allergy
For non-type I hypersensitivity reactions:
- Cephalexin: 20 mg/kg/dose twice daily (maximum 500 mg/dose) for 10 days 1
- Cefadroxil: 30 mg/kg once daily (maximum 1 g) for 10 days 1
For type I hypersensitivity or when cephalosporins are contraindicated:
- Clindamycin: 7 mg/kg/dose three times daily (maximum 300 mg/dose) for 10 days 1
- Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days 1
Important caveat: Macrolide resistance (azithromycin, clarithromycin) is well-documented and varies geographically and temporally 1. A study demonstrated that clarithromycin failed to eradicate 81-86% of clarithromycin-resistant Group A Streptococcus isolates, making it unreliable in areas with high resistance 8.
Common Pitfalls to Avoid
- Do not use lower doses: The traditional 40 mg/kg/day dosing is inadequate for optimal eradication 7, 9
- Do not shorten the course: Even with rapid symptom resolution, the full 10 days is mandatory to prevent rheumatic fever 1, 2, 4
- Do not rely on macrolides in high-resistance areas: Check local resistance patterns before prescribing azithromycin or clarithromycin 1, 8
- Ensure proper reconstitution: Oral suspension must be shaken well before each use and discarded after 14 days 4