Amoxicillin Dosing for a 33-Pound Child
For a 33-pound (15 kg) child with a typical infection, administer amoxicillin 45 mg/kg/day divided into 2 doses (approximately 340 mg twice daily), which translates to roughly 7 mL of 125 mg/5 mL suspension twice daily. 1
Standard Dosing Framework
The appropriate dose depends on the infection type and severity:
Mild to Moderate Infections
- Standard dose: 45 mg/kg/day divided every 12 hours 1, 2
- For a 15 kg child: 675 mg/day total (approximately 340 mg per dose)
- Using 125 mg/5 mL suspension: 13.5 mL/day (6.8 mL per dose, rounded to 7 mL twice daily)
- This covers most respiratory tract infections, skin infections, and ear infections 1, 2
Severe Infections or High-Resistance Areas
- High dose: 90 mg/kg/day divided every 12 hours 1, 3
- For a 15 kg child: 1,350 mg/day total (approximately 675 mg per dose)
- Using 125 mg/5 mL suspension: 27 mL/day (13.5 mL per dose twice daily)
- This regimen is indicated when penicillin-resistant Streptococcus pneumoniae or β-lactamase-producing organisms are suspected 1, 3
Infection-Specific Recommendations
Respiratory Tract Infections (Pneumonia, Sinusitis)
- Start with 45 mg/kg/day for mild-moderate cases 1
- Escalate to 90 mg/kg/day if: 1, 3
- Child attends daycare
- Recent antibiotic use within past 3 months
- Geographic area with high pneumococcal resistance
- No clinical improvement within 48-72 hours
Acute Otitis Media
- Standard dose (45 mg/kg/day) is appropriate for most cases 4, 5
- High dose (80-90 mg/kg/day) is indicated for: 4, 6
- Children in daycare settings
- Recent antibiotic exposure within 4-6 weeks
- Failed initial therapy after 48-72 hours
Group A Streptococcal Pharyngitis (Strep Throat)
- Dose: 50-75 mg/kg/day divided into 2 doses for 10 days 1
- For a 15 kg child: 750-1,125 mg/day (375-560 mg per dose)
- Must complete full 10-day course to prevent acute rheumatic fever 2, 7
Critical Dosing Considerations
Maximum Dose Limits
- Absolute maximum: 4,000 mg/day regardless of weight 3
- For this 15 kg child, even the high-dose regimen (1,350 mg/day) is well below this ceiling
Treatment Duration
- Minimum 48-72 hours beyond symptom resolution 1, 2
- 10 days for streptococcal infections 1, 2
- 7-10 days for most respiratory infections 1
Administration Guidelines
- Give at the start of meals to minimize gastrointestinal side effects 2
- Shake oral suspension well before each use 2
- Refrigeration preferred but not required; discard after 14 days 2
Common Pitfalls to Avoid
Underdosing in High-Risk Scenarios
The older recommendation of 40 mg/kg/day is inadequate for resistant organisms, particularly during viral coinfection 8. Research demonstrates that viral coinfection reduces amoxicillin middle ear fluid penetration, with mean concentrations dropping to 2.7 mcg/mL in virus-infected children versus 5.7 mcg/mL in bacterial-only infections 8.
Premature Discontinuation
- Clinical improvement should occur within 48-72 hours 1
- If no improvement by this timeframe, reevaluate and consider switching to amoxicillin-clavulanate (Augmentin) at 90 mg/kg/day of the amoxicillin component 1, 4
Dosing Errors with Suspension
- Ensure correct concentration is used (125 mg/5 mL vs 250 mg/5 mL) 2
- For 250 mg/5 mL suspension, the 15 kg child would receive 3.4 mL twice daily for standard dosing
When to Escalate Therapy
Switch to high-dose amoxicillin-clavulanate (90 mg/kg/day) if: 1, 4
- No improvement after 48-72 hours of standard amoxicillin
- Suspected β-lactamase-producing organisms (H. influenzae, M. catarrhalis)
- Recent antibiotic failure
- Severe infection at presentation