Amoxicillin Dosing for Tonsillitis in a 28.4kg Patient
For a 28.4kg child with tonsillitis, prescribe amoxicillin 250mg/5ml suspension: 14.2ml (710mg) twice daily for 10 days.
Dosing Calculation
- Weight-based dosing: The IDSA guideline recommends 25 mg/kg twice daily (maximum 500 mg per dose) for children with group A streptococcal pharyngitis 1
- Calculation: 28.4 kg × 25 mg/kg = 710 mg per dose
- Volume: 710 mg ÷ 50 mg/ml = 14.2 ml per dose
- Frequency: Twice daily (BID) dosing 1
- Duration: 10 days 1
Alternative Dosing Option
An alternative once-daily regimen is also guideline-supported:
- 50 mg/kg once daily (maximum 1,000 mg) 1
- This would be: 28.4 kg × 50 mg/kg = 1,420 mg once daily = 28.4 ml once daily
- However, twice-daily dosing is preferred as meta-analysis data demonstrate that once-daily penicillin dosing shows decreased efficacy (12 percentage points lower cure rate), while once-daily amoxicillin maintains efficacy 2
Rationale for This Regimen
Amoxicillin is a first-line agent with strong evidence: The IDSA provides a "strong, high" quality recommendation for amoxicillin in treating streptococcal pharyngitis/tonsillitis 1. Twice-daily dosing has been validated as equally efficacious to more frequent dosing schedules in multiple studies 2.
Clinical and bacteriologic efficacy: Research demonstrates that amoxicillin achieves comparable clinical success rates (96%) and bacterial eradication rates (83-92%) to traditional 10-day penicillin V regimens 3, 4. The twice-daily schedule significantly improves compliance compared to three or four times daily dosing 2.
Important Caveats
- Penicillin allergy: If the patient has a documented penicillin allergy, alternative agents include cephalexin (20 mg/kg per dose twice daily, maximum 500 mg per dose) for non-immediate hypersensitivity reactions, or azithromycin/clarithromycin for immediate Type I reactions 1
- Complete the full course: Emphasize completing all 10 days even if symptoms resolve earlier, as shorter courses may not adequately prevent rheumatic fever 1
- Resistance considerations: Macrolides (azithromycin, clarithromycin) should be avoided as first-line therapy due to geographic variation in resistance patterns 3