Cefalexin Dosing for a 2-Year-Old, 13kg Child
For a 13kg child, give 2.5-5 mL of the 125mg/5mL suspension four times daily, or 1.25-2.5 mL of the 250mg/5mL suspension four times daily, based on the standard pediatric dosing of 25-50 mg/kg/day in divided doses. 1
Dosing Calculation
The FDA-approved pediatric dosing for cefalexin is 25-50 mg/kg/day in divided doses 1. For a 13kg child:
- Lower dose range: 25 mg/kg/day × 13kg = 325 mg/day ÷ 4 doses = 81.25 mg per dose
- Upper dose range: 50 mg/kg/day × 13kg = 650 mg/day ÷ 4 doses = 162.5 mg per dose
Volume Calculations by Formulation
Cefalexin 125mg/5mL suspension:
- Lower dose: 81.25 mg ÷ 25 mg/mL = 2.5 mL four times daily 1
- Upper dose: 162.5 mg ÷ 25 mg/mL = 5 mL four times daily 1
Cefalexin 250mg/5mL suspension:
- Lower dose: 81.25 mg ÷ 50 mg/mL = 1.25 mL four times daily 1
- Upper dose: 162.5 mg ÷ 50 mg/mL = 2.5 mL four times daily 1
Cefalexin 500mg capsule:
Not appropriate for this child. A 500mg capsule would deliver 38.5 mg/kg per dose (500mg ÷ 13kg), which exceeds the recommended single-dose maximum when given four times daily 1.
Clinical Guidance
Use the higher end of the dosing range (50 mg/kg/day) for more severe infections or less susceptible organisms 1. The FDA label specifically states that "for more severe infections or those caused by less susceptible organisms, larger doses may be needed" 1.
For streptococcal pharyngitis and uncomplicated skin infections, the total daily dose may be divided and administered every 12 hours (twice daily) instead of four times daily, which improves adherence 1. However, the question specifically requests four times daily dosing.
Treatment duration should be at least 7 days, and for β-hemolytic streptococcal infections, continue for at least 10 days 1.
Important Considerations
- Children have greater body water turnover and may require higher per-kilogram doses than adults to achieve therapeutic concentrations 2
- The suspension must be refrigerated after mixing and remains stable for 14 days 1
- Cefalexin achieves urinary concentrations of 500-1000 mcg/mL following standard doses, far exceeding the minimum inhibitory concentration for common urinary pathogens 2