Amoxicillin Dosing for Strep Pharyngitis in a 10-year-old Child Weighing 66.1kg
For a 66.1kg 10-year-old child with strep pharyngitis, the recommended dose of amoxicillin is 45-50 mg/kg/day divided into 2-3 doses daily for 10 days, which equals approximately 3000-3300 mg/day (1000-1650 mg per dose). 1
Dosing Recommendations
Standard Dosing Options
Standard dose: 45 mg/kg/day divided into 2-3 doses for 10 days 2
- For a 66.1kg child: approximately 3000 mg/day total
- Can be given as 1500 mg twice daily or 1000 mg three times daily
High dose: 80-90 mg/kg/day divided into 2 doses for 10 days (for areas with high prevalence of resistant S. pneumoniae) 2
- For a 66.1kg child: approximately 5300-5950 mg/day total
- However, maximum daily dose should not exceed 4000 mg/day 1
Administration Schedule Options
- Twice daily dosing: 1500 mg twice daily (most convenient) 3
- Three times daily dosing: 1000 mg three times daily 2
- Once daily dosing: Some evidence supports once-daily dosing (750-1000 mg) for improved compliance, though this is not in official guidelines 4, 5, 3
Important Considerations
Duration of Treatment
- Treatment must continue for a full 10 days to prevent acute rheumatic fever, even if symptoms resolve earlier 2, 1
- The 10-day duration is specifically recommended for Streptococcus pyogenes infections to prevent complications 1
Weight-Based Dosing Considerations
- Since this child weighs 66.1kg (exceeds 40kg), adult dosing parameters can be considered 1
- For adults, the FDA-approved dosing for mild/moderate infections is 500 mg every 12 hours or 250 mg every 8 hours 1
- For severe infections, 875 mg every 12 hours or 500 mg every 8 hours 1
Efficacy Considerations
- Amoxicillin remains the drug of choice for strep pharyngitis due to its effectiveness, safety, narrow spectrum, and low cost 2
- Studies show amoxicillin at 40-50 mg/kg/day is more effective than lower-dose penicillin for both clinical and bacteriologic cure 6
- Bacteriologic failure rates are comparable between once-daily and twice-daily dosing regimens 3
Common Pitfalls to Avoid
- Underdosing: Inadequate dosing may lead to treatment failure and increased risk of complications 6
- Insufficient duration: Stopping treatment early increases risk of rheumatic fever 2, 1
- Not accounting for weight: This child is at the upper end of pediatric weight range and requires appropriate dosing adjustment 1
- Not considering local resistance patterns: In areas with high S. pneumoniae resistance, higher dosing may be needed 2
For this 66.1kg 10-year-old with strep pharyngitis, the most appropriate dose would be 1500 mg twice daily for 10 days, which provides adequate coverage while maintaining convenient dosing for adherence 1, 3.