What is the appropriate cephalexin dose for a pediatric urinary tract infection in a child weighing 74 lb (≈34 kg) using the 250 mg/5 mL oral suspension?

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Cephalexin Dosing for Pediatric UTI: 74 lb Child

For a child weighing 74 lb (33.6 kg) with a urinary tract infection, prescribe cephalexin 850 mg (17 mL of the 250 mg/5 mL suspension) given every 12 hours for 7-14 days.

Dosing Calculation

The FDA-approved pediatric dosing for cephalexin is 25-50 mg/kg/day in divided doses 1. For UTIs specifically:

  • Weight: 74 lb = 33.6 kg
  • Standard dose: 25-50 mg/kg/day divided
  • Calculation: 33.6 kg × 25 mg/kg = 840 mg/day (minimum)
  • Practical dosing: 850 mg twice daily = 1,700 mg/day total (approximately 50 mg/kg/day)

Using the 250 mg/5 mL suspension:

  • 850 mg = 17 mL per dose
  • Given every 12 hours (twice daily)

Dosing Schedule Options

The FDA label supports twice-daily dosing for UTIs 1. Recent evidence confirms that cephalexin 500 mg twice daily is as effective as four-times-daily dosing for UTIs in adults 2, and the twice-daily regimen improves adherence without compromising efficacy.

For this 74 lb child, the practical options are:

  1. Preferred: 850 mg (17 mL) every 12 hours
  2. Alternative: 425 mg (8.5 mL) every 6 hours if twice-daily dosing is inadequate

Treatment Duration

7-14 days of therapy is recommended for pediatric UTIs 3, 1. The AAP guideline reaffirms this duration range 3. While some studies suggest 3-day courses may be effective for uncomplicated lower UTIs 4, the standard remains 7-14 days, particularly for febrile UTIs.

Important Caveats

  • Severe infections: If the UTI is severe or caused by less susceptible organisms, consider increasing to the higher end of the dosing range (up to 100 mg/kg/day divided every 6 hours) 1
  • Maximum daily dose: Do not exceed 4 grams per day 1
  • Renal function: Ensure normal renal function; dose adjustment may be needed in renal impairment 1
  • Culture guidance: Adjust therapy based on urine culture and sensitivity results 3

Practical Prescribing

Prescription: Cephalexin 250 mg/5 mL oral suspension, dispense 240 mL

  • Sig: Give 17 mL by mouth every 12 hours for 10 days
  • Storage: Refrigerate after reconstitution; discard after 14 days 1

The twice-daily dosing significantly improves adherence compared to four-times-daily regimens, which is critical for treatment success in pediatric patients.

References

4
Research

Three-day therapy with cephalexin for lower urinary tract infections in children.

Scandinavian journal of infectious diseases, 1984

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