First-Line Medications and Dosages for Pediatric UTI
For uncomplicated lower UTI in children ≥2 months, use amoxicillin-clavulanate or trimethoprim-sulfamethoxazole as first-line oral therapy, while for pyelonephritis or severe infections in newborns and young infants, initiate parenteral therapy with ampicillin plus an aminoglycoside or ampicillin plus a third-generation cephalosporin. 1
Age-Stratified Treatment Approach
Newborns and Young Infants (<3 months)
- Parenteral therapy is required with either:
- Ampicillin plus aminoglycoside (gentamicin), OR
- Ampicillin plus third-generation cephalosporin (ceftriaxone or cefotaxime) 1
- Gentamicin dosing varies by gestational and postnatal age 2:
- Gestational age <30 weeks, postnatal age <14 days: 5 mg/kg IV q48h
- Gestational age 30-34 weeks, postnatal age ≤14 days: 5 mg/kg IV q36h
- Gestational age ≥35 weeks, postnatal age >7 days: 5 mg/kg IV q24h
Infants and Children (3 months to 24 months)
For uncomplicated lower UTI (cystitis):
- First-line oral options 1:
- Amoxicillin-clavulanate (dosing based on amoxicillin component: 20-40 mg/kg/day divided q8-12h)
- Trimethoprim-sulfamethoxazole: 40 mg/kg sulfamethoxazole + 8 mg/kg trimethoprim per 24 hours, divided q12h for 10-14 days 3
- Nitrofurantoin: 5-7 mg/kg/day PO divided in 4 doses (maximum 100 mg/dose) for 7 days 2
For pyelonephritis (mild to moderate):
- Consider oral therapy if child can tolerate and appears well 1
- Same agents as above, with close monitoring for clinical improvement within 24-48 hours 1
For pyelonephritis (severe) or inability to tolerate oral:
- Ceftriaxone or cefotaxime (parenteral) 2, 1
- Alternative: Gentamicin (conventional dosing: 2-2.5 mg/kg IV q8h; once-daily dosing: 5-7.5 mg/kg IV q24h) 2
Children and Adolescents (>2 years)
For uncomplicated lower UTI:
- Trimethoprim-sulfamethoxazole 3, 4:
- Weight-based dosing every 12 hours:
- 22 lb (10 kg): 1 teaspoonful (5 mL)
- 44 lb (20 kg): 2 teaspoonfuls (10 mL)
- 66 lb (30 kg): 3 teaspoonfuls (15 mL)
- 88 lb (40 kg): 4 teaspoonfuls (20 mL)
- Weight-based dosing every 12 hours:
- Nitrofurantoin: 5-7 mg/kg/day divided in 4 doses 2
- Cephalexin: First-generation cephalosporin, narrow-spectrum option 5
For pyelonephritis:
- Ciprofloxacin (use with caution, specialist consultation suggested) 2, 6:
- Oral: 10-20 mg/kg q12h (maximum 750 mg/dose)
- IV: 6-10 mg/kg q8h (maximum 400 mg/dose)
- Ceftriaxone or cefotaxime (parenteral) 2
Critical Prescribing Considerations
Local Resistance Patterns
- Always consider local E. coli resistance data before selecting empiric therapy 1, 7
- Trimethoprim-sulfamethoxazole resistance has increased in many regions and should be avoided unless local susceptibility confirms <20% resistance 8, 7
- Amoxicillin monotherapy is no longer recommended due to high resistance rates 8
Common Pitfalls to Avoid
Nitrofurantoin misuse:
- Do NOT use nitrofurantoin for pyelonephritis or febrile UTI due to inadequate tissue penetration 2, 1
- Only appropriate for uncomplicated lower UTI/cystitis 2
Inappropriate diagnosis:
- Polymicrobial growth (>1 organism) suggests contamination, not true UTI 4
- Require pyuria (>5 WBC/hpf or positive leukocyte esterase) AND positive culture (≥50,000 CFU/mL catheterized; ≥100,000 CFU/mL clean catch) AND symptoms 4
Broad-spectrum overuse:
- Avoid empiric third-generation cephalosporins (cefixime) for uncomplicated UTI when narrow-spectrum options are appropriate 5
- Reserve broad-spectrum agents for severe infections or known resistant organisms 5
Monitoring Requirements
- Clinical improvement expected within 24-48 hours of appropriate therapy 1
- Adjust therapy based on culture and sensitivity results rather than continuing empiric treatment 1, 4
- Renal and bladder ultrasonography recommended for febrile infants with UTI to detect anatomic abnormalities 1