Amoxicillin Dosing for Streptococcal Pharyngitis in a 20 kg Child
For a 20 kg child with streptococcal pharyngitis using amoxicillin 400 mg/5 mL suspension, give 6.25 mL per dose, twice daily for 10 days.
Dosing Calculation
The recommended dose for Group A Streptococcus pharyngitis is 50 mg/kg/day divided into 2 doses 1:
- Total daily dose: 20 kg × 50 mg/kg = 1000 mg/day
- Per dose: 1000 mg ÷ 2 = 500 mg per dose
- Volume per dose: 500 mg ÷ (400 mg/5 mL) = 6.25 mL per dose
- Frequency: Every 12 hours (twice daily)
- Duration: 10 days 1, 2
Key Dosing Principles
Standard Dosing for Strep Throat
- The IDSA guideline specifies amoxicillin at 50 mg/kg once daily (maximum 1000 mg) or alternatively 25 mg/kg (maximum 500 mg) twice daily for 10 days 1
- The twice-daily regimen at 50 mg/kg/day total (25 mg/kg per dose) is equally effective and may improve compliance 1
- The 10-day duration is mandatory to prevent acute rheumatic fever, regardless of clinical improvement 1, 2
Important Caveats
- Do not confuse with high-dose amoxicillin: The 50-75 mg/kg/day dosing for Group A Streptococcus pharyngitis 3 differs from the 80-90 mg/kg/day used for pneumococcal infections with penicillin resistance 3
- Administer at the start of meals to minimize gastrointestinal intolerance 2
- Shake suspension well before each use and refrigerate after reconstitution (though not required) 2
- Discard unused suspension after 14 days of reconstitution 2
Clinical Considerations
- Children typically become non-contagious within 12-24 hours of starting amoxicillin, with 91% showing negative cultures by the next morning 4
- However, complete the full 10-day course even if symptoms resolve earlier to prevent rheumatic fever 1, 2
- If the child weighs significantly more or develops treatment failure, reassess for compliance, resistant organisms, or alternative diagnoses 5
- Penicillin and amoxicillin remain first-line agents with strong recommendation and high-quality evidence 1