Amoxicillin 500mg Twice Daily for a 33.5kg Child
Yes, 500mg amoxicillin twice daily is an appropriate and safe dose for a child weighing 33.5kg, falling well within recommended dosing guidelines for most common bacterial infections. 1, 2
Dosing Calculation and Rationale
For this 33.5kg child, 500mg twice daily provides approximately 30 mg/kg/day, which is within the standard dosing range for mild to moderate infections:
Standard dosing for mild to moderate infections is 25 mg/kg/day divided every 12 hours (500mg twice daily = 1000mg/day ÷ 33.5kg = 29.9 mg/kg/day) 1, 2
The FDA-approved dosing table specifically lists 500mg every 12 hours as the standard adult dose for mild to moderate ear/nose/throat, skin, and genitourinary infections 2
For pediatric patients weighing >40kg, the FDA recommends the adult dose of 500mg every 12 hours for mild/moderate infections 2
While this child weighs slightly less than 40kg, the dose of 500mg twice daily (approximately 30 mg/kg/day) falls comfortably within the recommended range of 25-45 mg/kg/day 1, 2
Infection-Specific Considerations
The appropriateness of this dose depends on the infection type and severity:
For Mild to Moderate Infections:
Streptococcal pharyngitis: 25 mg/kg twice daily (maximum 500mg per dose) is the standard recommendation, making 500mg twice daily appropriate 3
Otitis media: 40-45 mg/kg/day in 2 divided doses is recommended; this child would need approximately 670-755mg/day, so 500mg twice daily (1000mg/day) is slightly below optimal but acceptable for mild cases 1
For Severe or Resistant Infections:
Higher-dose therapy: For severe infections or suspected resistant organisms, 45 mg/kg/day (approximately 1500mg/day or 750mg twice daily) would be more appropriate 1, 2
Respiratory tract infections: For lower respiratory tract infections of any severity, 45 mg/kg/day divided every 12 hours is recommended, which would be approximately 750mg twice daily for this child 1, 2
Important Clinical Caveats
Key considerations to avoid underdosing:
For community-acquired pneumonia in children ≥5 years, the recommended dose is 90 mg/kg/day (maximum 4g/day), which would be approximately 1500mg twice daily for this child—significantly higher than 500mg twice daily 1
Underdosing can lead to treatment failure and promote antimicrobial resistance 1
Amoxicillin dosing recommendations have increased over time due to increasing pneumococcal resistance 1
Administration Guidelines
Practical administration considerations:
Amoxicillin can be given without regard to meals, though administration with food may improve gastrointestinal tolerability 2
Treatment duration should be at least 10 days for Streptococcus pyogenes infections to prevent acute rheumatic fever 2
For most other infections, continue treatment for 48-72 hours beyond symptom resolution 2
In summary, 500mg twice daily is appropriate for this 33.5kg child for mild to moderate infections, but consider increasing to 750mg twice daily for severe infections or suspected resistant pathogens. 1, 2