Cephalexin Dosage for UTI in a 5-Year-Old Child Weighing 56 Pounds
For a 5-year-old child weighing 56 pounds (approximately 25 kg) with a urinary tract infection, the recommended dose of cephalexin is 25-50 mg/kg/day divided into 4 doses (every 6 hours), which equals 625-1250 mg/day or approximately 156-312 mg per dose. 1
Dosage Calculation
The FDA-approved dosing for cephalexin in pediatric patients provides clear guidance:
- Standard pediatric dosage: 25-50 mg/kg/day divided into 4 doses 1
- For a 25 kg child:
- At 25 mg/kg/day: 625 mg/day ÷ 4 doses = 156 mg per dose
- At 50 mg/kg/day: 1250 mg/day ÷ 4 doses = 312 mg per dose
Administration Schedule Options
Four-times-daily regimen (preferred for UTI)
- 156-312 mg every 6 hours (q.i.d.)
Alternative twice-daily regimen (for improved adherence)
- For streptococcal pharyngitis and skin/skin structure infections, twice-daily dosing is FDA-approved
- However, for UTIs, the four-times-daily regimen is preferred to maintain consistent antibiotic levels 1
Practical Administration
Using the available suspension formulations:
- With 250 mg/5 mL suspension: 3-6 mL (approximately 1/2-1 teaspoon) four times daily
- With 125 mg/5 mL suspension: 6-12 mL (approximately 1-2 teaspoons) four times daily
Duration of Therapy
For uncomplicated UTIs, therapy should be continued for 7-14 days 1
Special Considerations
Severity assessment: For severe infections, the higher end of the dosage range (50 mg/kg/day) is recommended 1
Renal function: No dose adjustment is needed unless severe renal impairment is present (glomerular filtration rate less than 30 mL/min) 2
Administration timing: Cephalexin is absorbed in the upper intestine rather than the stomach, so timing relative to meals is less critical than with some other antibiotics 2
Common pitfall: Underdosing is a common error in pediatric UTI treatment. Using the full recommended dose is important to achieve therapeutic concentrations in the urinary tract 2
Storage after reconstitution: After mixing the suspension, it should be stored in the refrigerator and may be kept for 14 days without significant loss of potency 1
Monitoring
- Clinical improvement should be assessed within 48-72 hours
- If no improvement is seen after 48 hours, consider alternative antibiotics
- Monitor for side effects, particularly gastrointestinal symptoms and allergic reactions
Alternative Approaches
While a three-day course of cephalexin (25-50 mg/kg/day) has shown effectiveness for lower UTIs in some studies 3, the FDA-approved recommendation for UTI treatment is 7-14 days 1. The shorter course may be considered only for uncomplicated lower UTIs with close follow-up.
Recent research has explored three-times-daily dosing of cephalexin at a higher dose (45 mg/kg/dose, maximum 1.5 g) for bone and joint infections with good efficacy and tolerability 4, but this regimen has not been specifically validated for UTIs and should not replace the standard four-times-daily dosing for UTI treatment.