Amoxicillin Dosing for Streptococcal Pharyngitis in an 80 kg, 11-Year-Old
For this 80 kg, 11-year-old patient with strep throat, prescribe amoxicillin 1000 mg once daily for 10 days, which is the maximum dose recommended by current guidelines. 1
Weight-Based Dosing Calculation
- The American Academy of Family Physicians recommends 50 mg/kg once daily (maximum 1000 mg) for children with streptococcal pharyngitis 1
- For this 80 kg patient, the calculated dose would be 4000 mg, but the maximum dose is capped at 1000 mg once daily 1
- Alternative dosing: 25 mg/kg twice daily (maximum 500 mg per dose) can be used, which would be 500 mg twice daily for this patient 1
Treatment Duration and Key Points
- Complete the full 10-day course even if symptoms resolve earlier—this is essential to prevent acute rheumatic fever 2, 1
- The patient becomes non-contagious after 24 hours of antibiotic therapy 2
- This dosing carries a "Strong, high" recommendation based on quality evidence 1
Advantages of Once-Daily Dosing
- Once-daily amoxicillin (1000 mg) has been shown to be non-inferior to twice-daily dosing in large controlled trials 3
- Better adherence is expected with once-daily dosing compared to multiple daily doses 1
- Amoxicillin has a narrow spectrum of activity with few adverse effects 1
Clinical Evidence Supporting This Approach
- Studies demonstrate that amoxicillin at 40-50 mg/kg/day achieves significantly higher clinical and bacteriologic cure rates compared to lower-dose penicillin V 4
- The once-daily formulation at 50 mg/kg (maximum 1000 mg) has been FDA-approved for patients 12 years and older and shown effective in comparative trials 2
- Meta-analyses confirm that once-daily amoxicillin maintains efficacy, unlike once-daily penicillin which shows decreased cure rates 5
Important Caveat
While this patient's weight-based calculation exceeds the maximum dose, do not exceed 1000 mg once daily—the maximum dose has been established for safety and efficacy in clinical trials 1, 3