Amoxicillin Dosing for a 15.5 kg Pediatric Patient
For a child weighing 15.5 kg, amoxicillin should be dosed at 40-45 mg/kg/day divided every 8-12 hours (620-698 mg/day total) for severe infections or lower respiratory tract infections, or 20-25 mg/kg/day divided every 8-12 hours (310-388 mg/day total) for mild to moderate infections. 1
Weight-Based Dosing Calculation
The American Academy of Pediatrics provides clear weight-based dosing guidelines that must be followed for children under 40 kg rather than fixed adult doses 1:
For Mild to Moderate Infections
- Dose: 20-25 mg/kg/day divided every 8-12 hours 1
- For 15.5 kg: 310-388 mg/day total
- Practical dosing: 155-194 mg per dose if given twice daily, or 103-129 mg per dose if given three times daily
For Severe Infections or Lower Respiratory Tract Infections
- Dose: 40-45 mg/kg/day divided every 8-12 hours 1
- For 15.5 kg: 620-698 mg/day total
- Practical dosing: 310-349 mg per dose if given twice daily, or 207-233 mg per dose if given three times daily
Available Formulations and Practical Administration
British Thoracic Society guidelines provide age-based dosing that can serve as a cross-reference for a child weighing 15.5 kg (typically 3-6 years old) 2:
- Standard suspension formulations allow for precise weight-based dosing 2
- For a child in this weight range, typical formulations would deliver approximately 125-250 mg per dose depending on infection severity 2
Clinical Context and Infection Severity
The choice between standard and high-dose amoxicillin depends on the clinical scenario 1:
- Use 20-25 mg/kg/day for: uncomplicated otitis media, mild skin infections, uncomplicated urinary tract infections
- Use 40-45 mg/kg/day for: community-acquired pneumonia, acute otitis media with treatment failure, suspected resistant organisms, severe infections
Recent evidence from the CAP-IT trial supports that higher doses (70-90 mg/kg/day) may be used for pneumonia, though standard high-dose therapy (40-45 mg/kg/day) remains the guideline recommendation 3
Critical Dosing Principles
Always calculate pediatric doses based on actual body weight in kilograms, never use adult fixed doses 1, 4. The Pediatric Pharmacy Association emphasizes that patient weight in kilograms should be required on all medication prescriptions to prevent dosing errors 4.
Common Pitfalls to Avoid
- Do not use adult fixed doses (e.g., 500 mg three times daily) for children under 40 kg 1
- Do not round to convenient tablet strengths without ensuring the dose falls within the appropriate mg/kg range 1
- Verify the infection type before selecting standard versus high-dose therapy, as underdosing resistant organisms can lead to treatment failure 3
- Ensure proper measurement devices are provided for liquid formulations to achieve accurate dosing 4
Duration of Therapy
Treatment duration should be based on the specific infection 2, 3: