Amoxicillin Dosing for a 15-Year-Old Weighing 67 kg
Yes, amoxicillin 1 g TID (three times daily) is an appropriate dose for a 15-year-old who weighs 67 kg, as this falls within standard adult dosing parameters which apply to adolescents 15 years and older regardless of weight.
Rationale for Dosing
According to the American Thoracic Society/Centers for Disease Control and Prevention/Infectious Diseases Society of America guidelines, adult dosing for antimicrobials begins at age 15 years, regardless of the patient's weight 1. This means that a 15-year-old patient should receive standard adult dosing for amoxicillin.
The standard adult dose of amoxicillin for moderate to severe infections is 500-875 mg every 8 hours (TID) or 750-1000 mg every 12 hours, with a maximum daily dose of 3000 mg. For this 15-year-old patient:
- Weight-based calculation: At 67 kg, even using high-dose amoxicillin (80-90 mg/kg/day) would result in 5360-6030 mg/day
- Adult standard dosing: 1 g TID = 3000 mg/day
Age-Based vs. Weight-Based Considerations
For children under 15 years, dosing is typically weight-based:
- For children <40 kg: 40-90 mg/kg/day divided into 2-3 doses
- For children ≥40 kg: Adult dosing applies
However, for a 15-year-old patient, the guidelines specifically indicate that adult dosing should be used 1. This is important because:
Recent research shows that larger children often receive lower than recommended doses per kilogram when clinicians become concerned about exceeding "adult doses" 2
The 2014 British National Formulary revisions addressed widespread concerns about underdosing of amoxicillin in children, highlighting the importance of appropriate dosing 3
Clinical Considerations
When treating infections that typically require amoxicillin, the following should be considered:
For Group A streptococcal pharyngitis: The Infectious Diseases Society of America recommends amoxicillin 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1
For complicated intra-abdominal infections: The Surgical Infection Society and IDSA guidelines recommend weight-based dosing for children, but adult dosing begins at age 15 1
For certain resistant pathogens: Higher doses may be warranted, but the maximum adult daily dose of 3 g should generally not be exceeded
Potential Pitfalls
Underdosing risk: Some clinicians may hesitate to give "full adult doses" to adolescents, but this can lead to underdosing and potential treatment failure. Research shows that larger children are often prescribed declining doses in mg/kg/day 2.
Overdosing concern: While the 1 g TID dose is within the standard adult range, it does represent the maximum recommended daily dose (3 g/day). Monitor for gastrointestinal side effects.
Duration of therapy: Ensure appropriate duration based on the indication (e.g., 10 days for streptococcal pharyngitis).
In conclusion, amoxicillin 1 g TID is appropriate for this 15-year-old patient weighing 67 kg, as it aligns with adult dosing guidelines which apply to patients 15 years and older.