Cephalexin Dosing for an 8-Year-Old Male Weighing 36 kg
The appropriate dose of cephalexin for this 8-year-old male weighing 36 kg is 25-50 mg/kg/day divided into 4 doses, which equals 225-450 mg four times daily.
Dosing Calculation
Based on the FDA-approved dosing guidelines for cephalexin in pediatric patients:
- Standard pediatric dosage: 25-50 mg/kg/day divided into 4 doses 1
- For this 36 kg child:
- Minimum dose: 36 kg × 25 mg/kg/day = 900 mg/day ÷ 4 = 225 mg four times daily
- Maximum dose: 36 kg × 50 mg/kg/day = 1800 mg/day ÷ 4 = 450 mg four times daily
Dosing Considerations by Infection Type
The specific dosing depends on the type and severity of infection:
- For standard skin and soft tissue infections: 25 mg/kg/day in 4 divided doses (225 mg four times daily) 2
- For streptococcal pharyngitis: The total daily dose may be divided and administered every 12 hours 1
- For more severe infections: Higher doses up to 50 mg/kg/day (450 mg four times daily) may be warranted 1
- For otitis media: Higher doses of 75-100 mg/kg/day in 4 divided doses are recommended 1
Alternative Dosing Regimens
While the FDA-approved dosing is 4 times daily, recent research suggests alternative regimens may be effective:
- For MSSA infections: 25 mg/kg/dose three times daily (300 mg three times daily) may achieve adequate pharmacodynamic targets 3, 4
- For bone and joint infections: 45 mg/kg/dose three times daily (maximum 1.5 g) has shown efficacy and good tolerability 5
Important Clinical Considerations
- Cephalexin should be administered for at least 10 days for treatment of β-hemolytic streptococcal infections 1
- The medication can be given with or without food
- Suspension formulations should be refrigerated after reconstitution and can be kept for 14 days 1
- For patients with renal impairment, dosage adjustment may be necessary 6
Practical Administration
For a 36 kg child, the following formulations could be used:
- Cephalexin 250 mg capsules: 1-2 capsules four times daily
- Cephalexin suspension (250 mg/5 mL): 4.5-9 mL four times daily
Remember that while less frequent dosing regimens (twice or three times daily) are emerging in the literature and may improve adherence, the FDA-approved dosing remains four times daily for most indications.