Amoxicillin Dosing for a 4-Year-Old Weighing 15.3 kg
For a 4-year-old child weighing 15.3 kg, the appropriate amoxicillin dose depends on the infection severity: for mild to moderate infections (such as uncomplicated otitis media or mild skin infections), give 310-383 mg/day divided into two doses (155-191 mg per dose twice daily), and for severe infections or lower respiratory tract infections (such as pneumonia), give 620-689 mg/day divided into two doses (310-345 mg per dose twice daily). 1
Weight-Based Dosing Algorithm
The dosing calculation follows this structured approach:
For Mild to Moderate Infections
- Standard dose: 20-25 mg/kg/day divided every 12 hours 1
- For 15.3 kg child: 306-383 mg/day total
- Practical dosing: Approximately 155-191 mg per dose given twice daily 1
- Indications: Uncomplicated otitis media, mild skin infections, uncomplicated urinary tract infections 1
For Severe Infections or Lower Respiratory Tract Infections
- High dose: 40-45 mg/kg/day divided every 12 hours 1, 2
- For 15.3 kg child: 612-689 mg/day total
- Practical dosing: Approximately 310-345 mg per dose given twice daily 1
- Indications: Community-acquired pneumonia, acute otitis media with treatment failure, suspected resistant organisms, severe infections 1, 2
Available Formulations and Administration
The oral suspension formulation is most appropriate for this age and weight:
- 125 mg/5 mL suspension: For mild infections, give approximately 6-7.5 mL per dose twice daily 3
- 250 mg/5 mL suspension: For severe infections, give approximately 6-7 mL per dose twice daily 3
- Administration: Give at the start of meals to minimize gastrointestinal intolerance 3
Clinical Context Matters
The infection type determines which dosing regimen to use:
Use 20-25 mg/kg/day for:
- Uncomplicated acute otitis media 1, 4
- Mild skin and soft tissue infections 1
- Uncomplicated urinary tract infections 1
Use 40-45 mg/kg/day (high-dose) for:
- Community-acquired pneumonia 2, 1
- Acute otitis media with recent antibiotic exposure or treatment failure 4
- Areas with high rates of penicillin-resistant Streptococcus pneumoniae 2
- Severe infections requiring hospitalization 2
Critical Pitfalls to Avoid
Never use adult fixed doses for children under 40 kg—always calculate based on actual body weight in kilograms 1. A common error is prescribing 250 mg or 500 mg tablets without weight-based calculation, which can lead to significant underdosing or overdosing.
Do not round to convenient tablet strengths without ensuring the dose falls within the appropriate mg/kg range 1. For this 15.3 kg child, rounding down to 125 mg twice daily (16 mg/kg/day) would provide inadequate coverage even for mild infections.
Avoid standard-dose amoxicillin (40-45 mg/kg/day) for acute otitis media in current practice, as high-dose amoxicillin (80-90 mg/kg/day) is now recommended as first-line therapy to provide adequate coverage against resistant S. pneumoniae 4. However, the evidence I've cited uses 40-45 mg/kg/day as the "high dose" for severe infections 1, while acute otitis media guidelines specifically recommend 80-90 mg/kg/day 4. This discrepancy reflects evolving resistance patterns—for acute otitis media specifically, use 80-90 mg/kg/day (1224-1377 mg/day for this child, or approximately 612-689 mg per dose twice daily).
Duration of Therapy
Treatment duration varies by infection type:
- Most infections: 7-10 days 1
- Streptococcal pharyngitis: Minimum 10 days to prevent acute rheumatic fever 3
- Severe infections: Up to 14 days depending on clinical response 1
- Continue therapy: 48-72 hours beyond symptom resolution or evidence of bacterial eradication 3
Special Considerations
For this specific patient (15.3 kg, 4 years old):
- No renal dose adjustment needed unless severe renal impairment is present (GFR <30 mL/min) 3
- Ensure accurate weight measurement on all prescriptions to prevent dosing errors 1
- Reassess at 48-72 hours if symptoms worsen or fail to improve, as this may indicate treatment failure requiring alternative therapy 4