Amoxicillin Dosing for a 130-Pound Twelve-Year-Old
For a 12-year-old weighing 130 pounds (approximately 59 kg), the recommended dose of amoxicillin is 45 mg/kg/day in divided doses every 12 hours or 40 mg/kg/day in divided doses every 8 hours for moderate to severe infections. 1
Weight-Based Dosing Calculation
When calculating the appropriate dose for this child:
- Weight: 130 pounds = 59 kg
- Since the child weighs more than 40 kg, adult dosing guidelines can be considered, but weight-based dosing is still preferred for precision
Dosing Options Based on Infection Severity:
For Mild/Moderate Infections:
- 25 mg/kg/day divided every 12 hours or 20 mg/kg/day divided every 8 hours 1
- For this child: approximately 1475 mg/day (divided as 737.5 mg twice daily or 492 mg three times daily)
For Moderate/Severe Infections:
- 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours 1
- For this child: approximately 2655 mg/day (divided as 1327.5 mg twice daily or 885 mg three times daily)
Practical Administration Guidelines
- Standard available dosage forms include 250 mg, 500 mg, and 875 mg tablets or capsules
- For twice-daily dosing of moderate/severe infections: 1250-1500 mg twice daily (using 500 mg + 750 mg tablets or 875 mg + 375 mg tablets)
- For three-times-daily dosing: 875 mg three times daily
- Maximum daily dose should not exceed 4 g/day 2
- Take at the start of a meal to minimize gastrointestinal intolerance 1
Treatment Duration Considerations
- Treatment should continue for a minimum of 48-72 hours beyond symptom resolution 1
- For streptococcal infections, a minimum of 10 days of treatment is recommended to prevent acute rheumatic fever 1
- For uncomplicated infections, 5-7 days is typically sufficient 2
Important Monitoring and Precautions
- Assess for improvement within 48-72 hours of starting treatment
- Monitor for common adverse effects including diarrhea, nausea, vomiting, and rash
- Patients with severe renal impairment (GFR <30 mL/min) should not receive the 875 mg dose 1
Dosing Frequency Considerations
While the FDA label recommends both twice-daily and three-times-daily options, recent evidence suggests that twice-daily dosing may be preferred for improved adherence while maintaining comparable efficacy for most common infections 3, 4.
The FDA-approved dosing guidelines provide the most authoritative recommendation for this patient, with weight-based dosing being more precise than age-based approaches, particularly for children who may be larger or smaller than average for their age.