Amoxicillin Dosing for an 11-Year-Old Weighing 104 lbs
Yes, it is appropriate to give adult-dose amoxicillin (500 mg every 12 hours or 875 mg every 12 hours depending on severity) to an 11-year-old boy weighing 104 pounds (47.3 kg), as children weighing more than 40 kg should be dosed as adults according to FDA labeling and established guidelines. 1
Weight-Based Dosing Threshold
The FDA-approved amoxicillin labeling explicitly states that pediatric patients aged 3 months and older who weigh greater than or equal to 40 kg should receive adult dosing regimens. 1
At 104 pounds (47.3 kg), this child exceeds the 40 kg threshold by a significant margin, placing him squarely in the adult dosing category. 1
Multiple endocarditis prophylaxis guidelines from the American Heart Association reinforce this principle, stating that "children weighing more than 40 kg should be dosed as adults" and that "total children's dose should not exceed adult dose." 2
Standard Adult Dosing Regimens
For mild to moderate infections (ear/nose/throat, skin/skin structure, genitourinary tract):
- 500 mg every 12 hours OR 250 mg every 8 hours 1
For severe infections or lower respiratory tract infections:
- 875 mg every 12 hours OR 500 mg every 8 hours 1
Why Weight-Based Calculation Is Not Needed Here
If you were to calculate the dose using pediatric weight-based dosing (25-45 mg/kg/day), this 47.3 kg child would require 1,182-2,129 mg/day, which falls within or below the adult dosing range of 1,000-1,750 mg/day for standard infections. 1
The adult dose is actually more conservative than strict weight-based dosing would suggest, making it both safe and appropriate. 1
Research confirms that children aged 2 years and older are pharmacokinetically mature and differ from adults only in size, not in drug metabolism or elimination. 3
Important Clinical Considerations
Renal function: Ensure normal kidney function, as patients with severe renal impairment (GFR <30 mL/min) should not receive the 875 mg dose. 1
Duration: Continue treatment for at least 48-72 hours beyond symptom resolution, with a minimum of 10 days for streptococcal infections to prevent rheumatic fever. 1
Administration: Give at the start of meals to minimize gastrointestinal intolerance. 1
Common Pitfall to Avoid
Do not automatically default to pediatric weight-based dosing formulas for children over 40 kg—this can lead to unnecessarily complex calculations and potential dosing errors when the simpler adult dosing regimen is both appropriate and FDA-approved for this weight range. 1, 4