Cephalexin Dosing for 11-Year-Old Child Weighing 95 lb (43 kg)
For this 11-year-old child weighing 43 kg, administer cephalexin 25-50 mg/kg/day divided into 3-4 doses, which translates to approximately 1,075-2,150 mg total daily dose, typically given as 250-500 mg every 6-8 hours depending on infection severity.
Standard Dosing Algorithm
The FDA-approved pediatric dosing for cephalexin is 25-50 mg/kg/day in divided doses 1. For this specific patient:
Calculation for 43 kg child:
Lower range: 25 mg/kg/day = 1,075 mg/day
- Divided every 6 hours (QID): ~270 mg per dose → 250 mg QID
- Divided every 8 hours (TID): ~360 mg per dose → 375 mg TID
Upper range: 50 mg/kg/day = 2,150 mg/day
- Divided every 6 hours (QID): ~540 mg per dose → 500 mg QID
- Divided every 8 hours (TID): ~715 mg per dose → 750 mg TID
Infection-Specific Dosing
For Skin and Soft Tissue Infections (MSSA):
Preferred dosing: 75-100 mg/kg/day in 3-4 divided doses 2, 3
- For this 43 kg child: 3,225-4,300 mg/day
- Practical dose: 750-1,000 mg every 6-8 hours (maximum 4 g/day per FDA label) 1
For Streptococcal Pharyngitis or Uncomplicated Infections:
Standard dosing: 25-50 mg/kg/day divided every 12 hours is acceptable 1
- For this child: 500 mg twice daily is appropriate for less severe infections
For More Severe Infections:
Higher dosing: 50-75 mg/kg/day in divided doses 4
- For this 43 kg child: 2,150-3,225 mg/day
- Practical dose: 500-750 mg every 6-8 hours
Recent Evidence on Dosing Frequency
Recent pharmacokinetic studies support less frequent dosing to improve adherence 5, 6, 7:
Three times daily dosing: 45 mg/kg/dose (maximum 1.5 g) TID has shown 99% cure rates in bone and joint infections 5
- For this 43 kg child: 1,935 mg/day = approximately 650 mg TID (or practical dose of 750 mg TID)
Twice daily dosing: Requires higher per-dose amounts (22-45 mg/kg/dose for MIC ≤2 mg/L) 7
- For this child: 950-1,935 mg per dose BID (practical: 1,000 mg BID)
Practical Recommendations by Clinical Scenario
Mild-Moderate Skin Infections or Pharyngitis:
- 500 mg every 12 hours (1,000 mg/day total)
- Duration: 7-10 days for pharyngitis 1
Moderate-Severe Skin/Soft Tissue Infections:
- 500 mg every 6 hours (2,000 mg/day total) OR
- 750 mg every 8 hours (2,250 mg/day total)
- Duration: 7-14 days depending on response
Severe Infections (e.g., complicated MSSA):
- 750-1,000 mg every 6-8 hours (3,000-4,000 mg/day total)
- Maximum FDA-approved dose: 4 g/day 1
- Consider parenteral therapy if >4 g/day needed 1
Important Caveats
Maximum daily dose: The FDA label specifies that if doses >4 g/day are required, parenteral cephalosporins should be considered 1.
Dosing frequency trade-offs: While QID dosing is traditional, TID dosing at 45 mg/kg/dose (up to 1.5 g) achieves equivalent pharmacodynamic targets with better adherence 5, 7. For this 43 kg child, 750 mg TID represents a reasonable balance between efficacy and practicality.
Renal function: Standard dosing assumes normal renal function; adjust for impairment if present.
Pathogen considerations: These doses assume methicillin-susceptible organisms. For MRSA or resistant organisms, cephalexin is inappropriate 2, 3, 4.