Cephalexin Dosage for Pediatric Skin Infections
For children with skin infections, cephalexin should be dosed at 25-50 mg/kg/day divided into 3-4 doses (or every 6-8 hours), with a maximum single dose of 500 mg and maximum daily dose of 4 grams. For uncomplicated skin infections like impetigo or simple cellulitis, the standard 25-50 mg/kg/day range is appropriate, while more severe infections may require dosing toward the higher end of this range 1.
Standard Dosing Regimens
The FDA-approved dosing provides two practical approaches 1:
- Four times daily (every 6 hours): 25-50 mg/kg/day divided into 4 doses
- Twice daily (every 12 hours): For streptococcal pharyngitis and skin/skin structure infections, the total daily dose can be split into 2 doses
For methicillin-susceptible Staphylococcus aureus (MSSA) skin infections specifically, guidelines recommend oral cephalexin at 75-100 mg/kg/day divided into 3 or 4 doses 2, 3. This higher dosing range (75-100 mg/kg/day) from the IDSA/PIDS pneumonia guidelines, while written for pneumonia, reflects the preferred dosing for serious MSSA infections and can be extrapolated to moderate-to-severe skin infections.
Practical Weight-Based Dosing
Using the 125 mg/5 mL or 250 mg/5 mL suspension 1:
For 125 mg/5 mL suspension (four times daily):
- 10 kg child: 0.5-1 teaspoon every 6 hours
- 20 kg child: 1-2 teaspoons every 6 hours
- 40 kg child: 2-4 teaspoons every 6 hours
For 250 mg/5 mL suspension (four times daily):
- 10 kg child: 0.25-0.5 teaspoon every 6 hours
- 20 kg child: 0.5-1 teaspoon every 6 hours
- 40 kg child: 1-2 teaspoons every 6 hours
Dosing Frequency Considerations
Twice-daily dosing is equally effective as four-times-daily dosing for uncomplicated skin infections 4, 5. A study of 154 patients demonstrated >97% efficacy with both regimens when the total daily dose remained constant 4. This makes twice-daily dosing an excellent option to improve adherence, particularly for outpatient management.
Recent evidence supports high-dose three-times-daily regimens (45 mg/kg/dose, maximum 1.5 g) for more serious infections, showing 99% cure rates in bone and joint infections with good tolerability 6. While this data comes from bone infections, it suggests that for moderate-to-severe skin infections, higher doses given less frequently may be both effective and more practical.
Severity-Based Approach
Mild skin infections (simple impetigo, small abscesses after drainage):
- 25-50 mg/kg/day divided every 12 hours (twice daily)
- Duration: 7-10 days
Moderate skin infections (cellulitis, larger areas of involvement):
- 50-75 mg/kg/day divided every 8 hours (three times daily) or every 6 hours (four times daily)
- Consider high-dose regimen: 45 mg/kg/dose (max 1.5 g) three times daily 7, 6
- Duration: 7-10 days
Severe infections or step-down from IV therapy:
- 75-100 mg/kg/day divided every 6-8 hours
- Maximum 4 g/day
- Duration: Complete 10-14 days total therapy (IV + oral)
Important Clinical Caveats
MRSA coverage: Cephalexin is only effective against methicillin-susceptible S. aureus. If MRSA is suspected (purulent infection, prior MRSA, high local prevalence, treatment failure), clindamycin (30-40 mg/kg/day divided 3-4 times daily) or trimethoprim-sulfamethoxazole should be used instead 8.
Streptococcal infections: For Group A Streptococcus, the standard 25-50 mg/kg/day dosing is adequate, but treatment must continue for at least 10 days to prevent rheumatic fever 1.
Dosing in young infants: For infants 7-60 days old, 25 mg/kg/dose every 6-8 hours achieves appropriate pharmacodynamic targets 9. Avoid extrapolating adult or older pediatric dosing to neonates without specific guidance.
Storage: After reconstitution, the suspension must be refrigerated and remains stable for 14 days 1.
The key to successful treatment is matching the dosing intensity to infection severity while ensuring the regimen is practical enough for adherence. For most uncomplicated pediatric skin infections, 25-50 mg/kg/day divided twice daily provides excellent efficacy with superior convenience 10, 4.