How many milliliters of the 457 mg per 5 mL amoxicillin syrup should be administered to a 12‑year‑old child weighing 37.8 kg for a high‑dose co‑amoxiclav regimen (90 mg/kg/day amoxicillin)?

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Last updated: July 26, 2026 • View editorial policy

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Dosing Calculation for High-Dose Amoxicillin Syrup

Administer 15 mL of the 457 mg/5 mL amoxicillin syrup twice daily (every 12 hours) for 10 days.

Calculation Breakdown

For a 37.8 kg child requiring 90 mg/kg/day of amoxicillin:

  • Total daily dose needed: 37.8 kg × 90 mg/kg = 3,402 mg/day
  • Dose per administration (twice daily): 3,402 mg ÷ 2 = 1,701 mg per dose
  • Volume calculation: 1,701 mg ÷ (457 mg/5 mL) = 14.8 mL per dose
  • Practical rounding: 15 mL twice daily

This provides approximately 2,742 mg per day (91.4 mg/kg/day), which falls within the target high-dose range.

Rationale for High-Dose Regimen

The FDA label for co-amoxiclav 600 mg/5 mL (ES-600) specifically recommends 90 mg/kg/day divided every 12 hours for 10 days for pediatric patients 3 months and older 1. However, your available formulation is 457 mg/5 mL (not the ES-600 formulation), which requires volume adjustment to achieve the same amoxicillin dose.

The 457 mg/5 mL formulation is NOT interchangeable with other amoxicillin/clavulanate suspensions due to different clavulanate ratios 1. The calculation above ensures the child receives the appropriate amoxicillin component dose.

Clinical Context

High-dose amoxicillin (80-90 mg/kg/day) is the preferred empiric therapy for community-acquired pneumonia and other serious respiratory infections in children, particularly when pneumococcal resistance is a concern 2. The PIDS/IDSA guidelines specifically recommend amoxicillin 90 mg/kg/day in 2 doses for S. pneumoniae with penicillin MICs >2.0 μg/mL 2.

Administration Instructions

  • Timing: Give at the start of meals to minimize gastrointestinal intolerance 1
  • Shake well before each dose
  • Storage: Refrigeration preferred but not required; discard after 14 days 1
  • Duration: Complete the full 10-day course

Important Caveats

  • This child (12 years old, 37.8 kg) is approaching adult weight but still requires weight-based dosing—do not cap at adult maximum doses for serious infections requiring high-dose therapy 3
  • If using plain amoxicillin (not co-amoxiclav), the same 90 mg/kg/day dosing applies, but formulation concentration may differ 4
  • Monitor for treatment failure at 48-72 hours; lack of improvement warrants further investigation 2

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.