Keflex (Cephalexin) Dosing for Pediatric UTI
For a 3-year-old child weighing 17.7 kg with a urinary tract infection, prescribe cephalexin 50–100 mg/kg/day divided into 4 doses (approximately 220–440 mg every 6 hours) for 7–14 days. 1, 2
Specific Dosing Calculation
For this 17.7 kg child:
- Standard dose: 50 mg/kg/day = 885 mg/day divided into 4 doses = 220 mg every 6 hours
- Higher dose (for more severe infections): 100 mg/kg/day = 1,770 mg/day divided into 4 doses = 440 mg every 6 hours
The FDA-approved dosing for cephalexin in pediatric patients is 25–50 mg/kg/day in divided doses, though the AAP UTI guidelines specifically list 50–100 mg/kg/day in 4 doses for febrile UTIs 1, 2.
Treatment Duration
Treat for 7–14 days total. The 2011 AAP guideline for febrile UTIs in children 2–24 months recommends this range, as direct comparison data between 7,10, and 14 days were not available 1. A 2016 reaffirmation noted that a trial comparing 5 vs 10 days was underway, but no definitive shorter duration has been established 3.
Route of Administration
Oral administration is appropriate for this child if they can tolerate oral intake and do not appear toxic. The AAP guideline provides strong evidence (quality A) that oral and parenteral routes are equally efficacious for febrile UTIs 1. Reserve parenteral therapy for children who appear toxic, cannot retain oral medications, or when compliance is uncertain 1.
Key Considerations
Local Resistance Patterns
Check local susceptibility data before prescribing. The AAP guideline emphasizes knowing local coliform resistance patterns to cephalexin, as geographic variability is substantial 1. If local resistance exceeds 20%, consider alternative agents.
Alternative Oral Agents for UTI
If cephalexin is not appropriate based on local resistance:
- Amoxicillin-clavulanate: 20–40 mg/kg/day in 3 doses 1
- Trimethoprim-sulfamethoxazole: 6–12 mg/kg trimethoprim component in 2 doses 1
- Cefixime: 8 mg/kg/day in 1 dose 1
Common Pitfalls
Avoid nitrofurantoin for febrile UTIs. While nitrofurantoin achieves excellent urinary concentrations, it does not reach therapeutic serum levels needed to treat pyelonephritis or urosepsis, which cannot be reliably excluded in febrile children 1.
Do not underdose. Recent data show that pediatric URI dosing errors are common, with underdosing occurring frequently 4. For UTIs specifically, the higher end of the dosing range (75–100 mg/kg/day) may be more appropriate for febrile presentations.
Dosing Frequency Considerations
While the FDA label and AAP guidelines recommend 4-times-daily dosing 1, 2, emerging evidence in adults suggests twice-daily dosing may be effective for uncomplicated UTIs 5, 6. However, for a febrile 3-year-old, maintain the guideline-recommended 4-times-daily dosing until pediatric-specific data support less frequent administration.
Follow-up Imaging
Obtain renal and bladder ultrasound (RBUS) during or after treatment 1, 3. Routine voiding cystourethrography is no longer recommended after first febrile UTI unless RBUS shows hydronephrosis, scarring, or other concerning findings 3.