Cephalexin Dosing for Soft Tissue Infections
For uncomplicated skin and soft tissue infections in adults, cephalexin 500 mg orally every 6 hours (four times daily) for 7 days is the recommended regimen. 1, 2, 3
Standard Adult Dosing
- 500 mg orally every 6 hours (QID) is the standard dose for mild to moderate soft tissue infections 1, 2, 3
- Treatment duration is typically 7 days, but should be extended if the infection has not improved within this timeframe 1, 2
- The FDA-approved adult dosage range is 1-4 grams daily in divided doses 3
Alternative Dosing Schedule
- 500 mg every 12 hours (BID) may be administered for uncomplicated skin and skin structure infections 3
- Studies demonstrate that twice-daily dosing (500 mg or 1 g BID) achieves clinical cure rates exceeding 80% for soft tissue infections 4
- However, the four-times-daily regimen remains the guideline-recommended standard 1, 2
Pediatric Dosing
- 25-50 mg/kg/day divided into 3-4 doses (every 6-8 hours) for children 2, 3
- For streptococcal pharyngitis and skin infections in patients over 1 year, the total daily dose may be divided and given every 12 hours 3
- In severe infections, the pediatric dosage may be doubled 3
Critical Coverage Considerations
Cephalexin is ONLY appropriate for non-purulent cellulitis without MRSA risk factors. 1, 2
When Cephalexin is Appropriate:
- Mild cellulitis or erysipelas without systemic signs 1
- Infections likely caused by methicillin-susceptible Staphylococcus aureus (MSSA) and streptococci 1, 2
- Surgical site infections of trunk or extremity away from axilla or perineum 1
When to Choose Alternative Agents:
- MRSA risk factors present: penetrating trauma, evidence of MRSA infection elsewhere, nasal MRSA colonization, injection drug use, or systemic inflammatory response syndrome (SIRS) - use vancomycin, trimethoprim-sulfamethoxazole, doxycycline, or clindamycin instead 1, 2
- Purulent infections (abscesses, carbuncles) with systemic illness - use MRSA-active agents 2
- Animal or human bites - use amoxicillin-clavulanate for Pasteurella multocida and anaerobic coverage 2
- Diabetic foot infections or complicated soft tissue infections - broader spectrum antibiotics required 2
Clinical Efficacy Data
- Clinical response rates exceed 95% for uncomplicated soft tissue infections treated with cephalexin 5
- Non-inferiority to IV cefazolin plus probenecid demonstrated, with failure rates of only 4.2% at 72 hours 6
- Staphylococcus aureus is isolated in approximately 43% of soft tissue infections, with gram-negative rods in only 7% 5
Important Caveats
- Penicillin allergy: For patients with immediate hypersensitivity reactions to penicillins, cross-reactivity with cephalexin is possible; consider alternative agents 2
- Renal impairment: Patients with creatinine clearance <30 mL/min require dosage reduction proportional to reduced renal function 7
- Obtain cultures before starting antibiotics for recurrent soft tissue infections 2
- If daily doses >4 grams are required, parenteral cephalosporins should be considered 3