Cephalexin Dosing for Impetigo in a 102-Pound Child
For a child weighing 102 pounds (46.3 kg) with impetigo, administer cephalexin 25-50 mg/kg/day divided into 3-4 doses, which translates to 1,158-2,316 mg/day total, or approximately 290-580 mg per dose given four times daily (every 6 hours) for 10 days. 1
Specific Dosing Calculation
- Weight conversion: 102 pounds = 46.3 kg
- Standard dosing range: 25-50 mg/kg/day divided into 3-4 doses 1
- Total daily dose: 1,158-2,316 mg/day
- Per-dose amount (if given four times daily): 290-580 mg per dose 1
- Practical dosing: Use 500 mg four times daily (2,000 mg/day total, which equals 43 mg/kg/day and falls within the recommended range) 1
Rationale for This Dosing
Cephalexin is highly effective for impetigo because Staphylococcus aureus is the predominant pathogen (62% of cases as sole organism, 81% when including mixed infections), and cephalexin demonstrates superior efficacy compared to penicillin. 2 In a randomized controlled trial, cephalexin achieved 100% treatment success for impetigo compared to 76% with penicillin and 96% with erythromycin. 2
- The FDA-approved pediatric dosing for skin and soft tissue infections is 25-50 mg/kg/day in divided doses, with the option to divide the total daily dose every 12 hours specifically for skin infections. 1
- For more severe staphylococcal infections, the dosage may be doubled, and doses up to 75-100 mg/kg/day in 4 divided doses have been used. 1, 3
- The American Academy of Pediatrics recommends 75-100 mg/kg/day divided into 3-4 doses specifically for methicillin-susceptible S. aureus (MSSA) infections. 4
Treatment Duration and Monitoring
Administer cephalexin for a full 10-day course to ensure complete eradication of streptococcal organisms if present, as beta-hemolytic streptococcal infections require at least 10 days of therapy. 1
- Clinical improvement should be evident within 3-5 days, with efficacy rates of 90.4% by day 3 and 100% by days 5 and 7 in pediatric impetigo patients. 5
- Higher doses (30.1-45.0 mg/kg/day) showed 17.2% better efficacy rates and 45.3% higher "excellent" response rates compared to lower doses (22.5-30.0 mg/kg/day) by day 3. 5
Practical Administration
Use the 250 mg/5 mL oral suspension formulation for this child, administering 10 mL (500 mg) four times daily. 1
- According to the FDA dosing table, a 40 kg child (88 lb) receives 2-4 teaspoons (10-20 mL) of the 250 mg/5 mL suspension four times daily for standard dosing, or 4-8 teaspoons (20-40 mL) twice daily for the alternative twice-daily regimen. 1
- For a 46.3 kg child, 10 mL (500 mg) four times daily is appropriate and falls within the recommended range. 1
- The suspension must be refrigerated after mixing and remains stable for 14 days. 1
Important Clinical Considerations
Cephalexin provides excellent coverage for methicillin-susceptible S. aureus but has no activity against MRSA, so treatment failure by day 3-5 should prompt consideration of MRSA and switch to alternative antibiotics such as trimethoprim-sulfamethoxazole or clindamycin. 4
- Cephalexin can be used in patients with non-severe penicillin allergy but is contraindicated in those with history of anaphylaxis, angioedema, or urticaria to penicillins. 4
- The drug is absorbed high in the intestinal tract and does not disturb lower bowel flora, resulting in low gastrointestinal side effects (diarrhea occurs in approximately 4-8% of pediatric patients). 6, 7
- Twice-daily dosing (dividing the total daily dose into two doses given every 12 hours) is FDA-approved for skin infections and may enhance compliance, though four-times-daily dosing ensures more consistent drug levels. 1, 8