Amoxicillin Dosing for Strep Throat in a 33 kg Pediatric Patient
For a 33 kg child with streptococcal pharyngitis, prescribe amoxicillin 50 mg/kg once daily (1650 mg, rounded to 1500-1650 mg, maximum 1000 mg) OR 25 mg/kg twice daily (825 mg per dose, rounded to 750-825 mg, maximum 500 mg per dose) for 10 days. 1
Preferred First-Line Dosing Regimens
The Infectious Diseases Society of America establishes amoxicillin as the preferred oral antibiotic for pediatric strep throat, with two equivalent evidence-based options 1:
Once-daily dosing: 50 mg/kg once daily (maximum 1000 mg) for 10 days 1
- For this 33 kg patient: 1650 mg once daily, but capped at 1000 mg maximum dose 1
Twice-daily dosing: 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1
- For this 33 kg patient: 825 mg per dose (round to 750-825 mg), but capped at 500 mg per dose twice daily 1
Both regimens demonstrate equivalent efficacy with strong, high-quality evidence 1, 2.
Critical Dosing Considerations for This Weight Category
Since this patient weighs 33 kg (less than 40 kg), the FDA-approved dosing for ear/nose/throat infections indicates 3:
- Mild/moderate infections: 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 3
- Severe infections: 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 3
However, streptococcal pharyngitis is typically treated as a mild-to-moderate infection, and the IDSA guideline-recommended dosing of 50 mg/kg once daily or 25 mg/kg twice daily has been specifically validated for Group A Streptococcus 1, 4.
Practical Dosing Calculation for This Patient
For the 33 kg patient, calculate as follows:
Once-daily option: 33 kg × 50 mg/kg = 1650 mg once daily
- Practical dose: 1000 mg once daily (respecting maximum dose) 1
Twice-daily option: 33 kg × 25 mg/kg = 825 mg, divided into two doses = 412.5 mg per dose
- Practical dose: 400-500 mg twice daily 1
Treatment Duration is Non-Negotiable
All oral regimens must be completed for 10 full days to prevent acute rheumatic fever, regardless of symptom resolution 1, 3. This is a critical safety consideration, as inadequate treatment duration increases the risk of nonsuppurative complications 4.
Alternative Dosing from Community Pneumonia Guidelines
The pediatric community pneumonia guidelines recommend amoxicillin 50-75 mg/kg/day in 2 doses for Group A Streptococcus 4. For this 33 kg patient, this translates to:
- 1650-2475 mg/day total, divided into 2 doses = 825-1237.5 mg per dose
- Practical dosing: 750-1000 mg twice daily 4
However, this higher dosing is typically reserved for pneumonia rather than uncomplicated pharyngitis 4.
When NOT to Use Standard Amoxicillin
Reserve amoxicillin/clavulanate (Augmentin) for treatment failures or chronic GAS carriers who have failed first-line therapy 5, 1. The dosing for Augmentin in these scenarios is 40 mg/kg/day of the amoxicillin component divided into three doses (maximum 2000 mg/day) for 10 days 5, 1.
Evidence Supporting Once-Daily Dosing
A large noninferiority trial (n=652) demonstrated that once-daily amoxicillin (750 mg for <40 kg patients) had comparable bacteriologic failure rates to twice-daily dosing at 14-21 days (20.1% vs 15.5%, difference 4.53%, 90% CI -0.6 to 9.7) and actually superior rates at 28-35 days (2.8% vs 7.1%) 2. Real-time PCR studies confirm that once-daily dosing achieves equivalent bacterial eradication as multiple-daily dosing 6.
Common Pitfalls to Avoid
Do not underdose: Historical "typical" pediatric dosing of 40-45 mg/kg/day is now considered inadequate 4. Research demonstrates that 40 mg/kg/day amoxicillin achieves significantly better clinical (70.9% vs 87.9%, p=0.025) and bacteriologic cure (54.5% vs 79.3%, p=0.005) compared to lower-dose penicillin V 7.
Do not stop early: Even if the child becomes asymptomatic after 3-5 days, complete the full 10-day course 1, 3.
Do not use amoxicillin/clavulanate as first-line: This is specifically reserved for treatment failures and carriers 5, 1.
Administration Tips
Administer amoxicillin at the start of a meal to minimize gastrointestinal intolerance 3. If using oral suspension, shake well before each use and discard any unused portion after 14 days 3.