Amoxicillin Dosing for a 35-Pound (15.9 kg) Child
For a 35-pound (15.9 kg) child using amoxicillin 400mg/5mL suspension, the appropriate dose is 3.75 mL (300 mg) twice daily for mild to moderate infections or 7.5 mL (600 mg) twice daily for severe infections such as pneumonia. 1, 2
Weight-Based Dosing Calculation
A 35-pound child weighs approximately 15.9 kg, which falls into the pediatric dosing category of children under 40 kg who require weight-based dosing rather than fixed adult doses. 1, 2
For Mild to Moderate Infections
- Standard dose: 20-25 mg/kg/day divided every 12 hours 1, 2
- Calculation for 15.9 kg child:
- 20 mg/kg/day = 318 mg/day total (159 mg per dose twice daily)
- 25 mg/kg/day = 398 mg/day total (199 mg per dose twice daily)
- Practical dosing with 400mg/5mL suspension: Approximately 2-2.5 mL per dose (160-200 mg), which can be rounded to 2.5 mL (200 mg) twice daily 1
For Severe Infections or Pneumonia
- High dose: 40-45 mg/kg/day divided every 12 hours 1, 2
- Calculation for 15.9 kg child:
- 40 mg/kg/day = 636 mg/day total (318 mg per dose twice daily)
- 45 mg/kg/day = 716 mg/day total (358 mg per dose twice daily)
- Practical dosing with 400mg/5mL suspension: Approximately 4-4.5 mL per dose (320-360 mg), which can be rounded to 4 mL (320 mg) twice daily 1, 2
Infection-Specific Dosing Recommendations
The dose selection depends critically on the type and severity of infection:
Use Lower Dose (20-25 mg/kg/day) For:
Use Higher Dose (40-45 mg/kg/day) For:
- Community-acquired pneumonia 3, 1
- Acute otitis media with treatment failure 1
- Suspected resistant organisms 1
- Severe infections requiring hospitalization 3, 1
Administration Guidelines
Amoxicillin should be administered at the start of a meal to minimize gastrointestinal intolerance. 2
The 400mg/5mL suspension formulation allows for precise weight-based dosing in pediatric patients. 1 After reconstitution, shake the suspension well before each use, and any unused portion must be discarded after 14 days. 2 Refrigeration is preferable but not required. 2
Duration of Therapy
Treatment duration should be:
- Minimum 48-72 hours beyond symptom resolution or evidence of bacterial eradication 2
- At least 10 days for infections caused by Streptococcus pyogenes to prevent acute rheumatic fever 2
- 7-10 days for most bacterial infections 1
- Up to 14 days for severe infections depending on clinical response 1
Recent evidence from a large randomized trial demonstrated that 3-day courses were non-inferior to 7-day courses for uncomplicated pneumonia, though cough resolution was slightly faster with 7 days of treatment. 4 However, standard practice remains 7-10 days for most infections. 1, 2
Critical Pitfalls to Avoid
Never use adult fixed doses for children under 40 kg. 1 This child weighs significantly less than 40 kg and requires weight-based pediatric dosing, not adult dosing regimens.
Do not round to convenient volumes without ensuring the dose falls within the appropriate mg/kg range. 1 Always calculate the dose based on actual body weight in kilograms first, then determine the appropriate volume of suspension.
Ensure proper measurement using a calibrated oral dosing syringe or device that accurately measures the prescribed volume, not household spoons. 1
Do not underdose severe infections. For pneumonia, lower respiratory tract infections, or suspected resistant organisms, the higher dose range (40-45 mg/kg/day) is essential for optimal outcomes and prevention of treatment failure. 3, 1, 2