Cephalexin Dosing for Skin Infections in a 14-Year-Old
For a 14-year-old with a skin infection, administer cephalexin 25–50 mg/kg/day divided into 3–4 doses (or every 6–8 hours), with a maximum of 4 grams per day. 1, 2
Standard Dosing Regimen
The IDSA guidelines and FDA labeling provide clear dosing parameters for pediatric skin and soft tissue infections:
- Standard dose: 25–50 mg/kg/day divided into 3–4 doses orally 1
- Maximum daily dose: 4 grams 2
- Typical frequency: Every 6 hours (four times daily) or every 8 hours (three times daily) 1, 2
For a 14-year-old who likely weighs ≥40 kg, this translates to approximately 500 mg every 6 hours (2 grams/day total) for mild-to-moderate infections. 2
Simplified Dosing Options
Three times daily dosing is increasingly supported by recent evidence and improves adherence:
- 45 mg/kg/dose (maximum 1.5 g) three times daily achieves appropriate pharmacodynamic targets and has demonstrated 99% cure rates in pediatric bone and joint infections 3
- This regimen is better tolerated than four times daily dosing while maintaining efficacy 4, 5
Twice daily dosing may be considered for less severe infections:
- For streptococcal pharyngitis and uncomplicated skin infections, the total daily dose can be divided every 12 hours 2
- Research supports 22–45 mg/kg/dose twice daily for MSSA with MIC ≤2 mg/L 4
- Historical data from 1981 showed twice daily dosing was equally effective (>97% cure rate) as four times daily for skin infections 6
Severity-Based Approach
Mild-to-moderate infections (impetigo, simple cellulitis, uncomplicated wound infections):
- 25–50 mg/kg/day in 3–4 divided doses 1
- Consider simplified three times daily or twice daily regimens for improved adherence 4, 3
More severe infections or those caused by less susceptible organisms:
- Higher end of dosing range (50 mg/kg/day) 2
- Consider four times daily dosing initially 1
- If doses >4 g/day are needed, parenteral cephalosporins should be used instead 2
Critical Considerations
MRSA coverage: Cephalexin is not appropriate for confirmed or suspected MRSA infections, despite some older studies showing clinical response 7. The IDSA guidelines clearly distinguish MSSA from MRSA treatment algorithms, with clindamycin, trimethoprim-sulfamethoxazole, or doxycycline (if ≥8 years old) recommended for MRSA 1.
Duration: Continue therapy for at least 10 days for streptococcal infections 2. Most uncomplicated skin infections require 7–14 days of treatment 2.
Penicillin allergy: Cephalexin is appropriate for penicillin-allergic patients except those with immediate hypersensitivity reactions 1.
Common pitfall: The availability of suspension formulations and less frequent dosing requirements make cephalexin preferable to dicloxacillin in pediatrics, despite dicloxacillin being the "oral agent of choice" in adults 1.