Amoxicillin Dosing for Pediatric UTI
For a 2.5-year-old child weighing 15 kg with an uncomplicated urinary tract infection, prescribe amoxicillin 20-40 mg/kg/day divided every 12 hours (300-600 mg/day total, or 150-300 mg twice daily) for 7-10 days. 1
Recommended Dosing Strategy
The FDA-approved dosing for genitourinary tract infections in children ≥3 months and <40 kg is:
- Mild/Moderate infections: 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 2
- For this 15 kg child: 375 mg/day (187.5 mg twice daily) using the 25 mg/kg/day regimen
The 2011 AAP guideline for febrile UTI in children 2-24 months recommends amoxicillin-clavulanate at 20-40 mg/kg/day in 3 doses as an oral empiric option 1. While this guideline specifically addresses amoxicillin-clavulanate, plain amoxicillin remains appropriate if local resistance patterns support its use and the infection is uncomplicated.
Route of Administration
Oral therapy is appropriate for this child unless they appear toxic, are unable to retain oral intake, or compliance is uncertain 1. The 2011 AAP guideline demonstrated that oral and parenteral routes are equally efficacious for febrile UTI in children 2-24 months 1.
Duration of Therapy
Treat for 7-10 days 1. The AAP guideline recommends 7-14 days for febrile UTI, with most practitioners favoring 7-10 days for uncomplicated cases. Recent evidence from 2026 suggests that 5-day courses may be reasonable for uncomplicated febrile UTI in children showing clinical improvement 3, though this represents evolving practice rather than established guideline recommendations.
Key Clinical Considerations
- Administer at the start of meals to minimize gastrointestinal intolerance 2
- Local resistance patterns matter: Amoxicillin should only be used if local E. coli resistance rates are acceptable. If resistance exceeds 20%, consider amoxicillin-clavulanate or alternative agents 4
- Clinical improvement expected within 48-72 hours: If the child fails to improve or deteriorates, further investigation and antibiotic adjustment are needed 1
Common Pitfall
Avoid underdosing in this weight range. Research demonstrates that children in the 15 kg range typically receive appropriate dosing around 80 mg/kg/day for high-dose indications, but UTI requires lower doses 5. For this 15 kg child with UTI, the 20-40 mg/kg/day range (300-600 mg/day) is appropriate and should not be confused with high-dose amoxicillin (80-90 mg/kg/day) used for resistant pneumococcal infections.
Alternative Agents
If amoxicillin is inappropriate due to resistance or allergy: