Cephalexin Dosing for Pediatric Impetigo
Recommended Dose
For a 3.5-year-old child weighing 35 lbs (approximately 16 kg) with impetigo, administer cephalexin 25-50 mg/kg/day divided into 3-4 doses, which translates to 400-800 mg total daily dose, or approximately 200 mg four times daily (or 2 mL of 250 mg/5 mL suspension four times daily). 1
Dosing Algorithm
Standard Dosing Calculation
- Weight conversion: 35 lbs = 15.9 kg (approximately 16 kg) 1
- Standard dose range: 25-50 mg/kg/day for skin and skin structure infections 1
- Total daily dose: 400-800 mg/day 1
- Divided dosing: Given every 6 hours (four times daily) or every 12 hours (twice daily) 1
Practical Administration
- Using 250 mg/5 mL suspension: Give 1.5-2 mL (approximately 75-100 mg) four times daily 1
- Alternative twice-daily dosing: Give 3-4 mL (approximately 150-200 mg) twice daily for uncomplicated cases 1
- Duration: Continue treatment for at least 10 days, as impetigo is typically caused by β-hemolytic streptococci or Staphylococcus aureus 1, 2
Clinical Context and Rationale
Pathogen Coverage
- Cephalexin provides excellent coverage for both Staphylococcus aureus (the most common pathogen, accounting for 62% of cases) and Streptococcus pyogenes (group A beta-hemolytic streptococci) 3
- In comparative studies, cephalexin demonstrated 100% clinical cure rates for pediatric skin infections including impetigo 3, 4
Evidence for Efficacy
- Cephalexin has been shown to be more effective than penicillin V for impetigo treatment, with significantly lower treatment failure rates (0% vs 24%) 3
- Studies demonstrate that cephalexin 40-50 mg/kg/day is highly effective for impetigo, with cure rates comparable to or better than other oral antibiotics 3, 4
Important Clinical Considerations
Treatment Duration
- Minimum 10 days of therapy is required for β-hemolytic streptococcal infections to prevent complications such as poststreptococcal glomerulonephritis 1, 2
- Most cases resolve within 2-3 weeks without scarring when appropriately treated 2
When to Consider Alternatives
- If MRSA is suspected (based on local resistance patterns or treatment failure), switch to clindamycin 25-40 mg/kg/day divided into 3-4 doses 5, 2
- For extensive disease or treatment failure at 48-72 hours, consider topical mupirocin as an alternative or adjunct, which may be superior to oral antibiotics for localized disease 6
- If local MRSA prevalence is high (>10%), consider empiric clindamycin instead of cephalexin 2
Common Pitfalls to Avoid
- Do not use penicillin V alone, as it has unacceptably high failure rates (24%) due to poor coverage of S. aureus 3, 7
- Do not use topical disinfectants, as they are inferior to antibiotics and not recommended 2, 6
- Ensure full 10-day course completion even if lesions improve earlier, to prevent recurrence and complications 1, 2
Monitoring for Response
- Clinical improvement should be evident within 48-72 hours of initiating therapy 5
- If no improvement occurs by 8-10 days, consider treatment failure and reassess for MRSA or need for alternative therapy 3