Cephalexin (Keflex) for Skin Infections: Dosing and Recommendations
For uncomplicated skin and soft tissue infections caused by methicillin-susceptible Staphylococcus aureus (MSSA) or Streptococcus, cephalexin 500 mg orally four times daily (every 6 hours) for 7-10 days is the recommended treatment. 1, 2, 3
Standard Dosing Regimen
- Adults: 500 mg orally four times daily (every 6 hours) for 7-10 days 1, 2, 3
- The FDA-approved dosage range is 1-4 grams daily in divided doses 3
- For less severe infections, 500 mg every 12 hours may be adequate for streptococcal pharyngitis, skin infections, and uncomplicated cystitis 3
- Treatment duration is typically 7 days, adjusted based on clinical response 2
When Cephalexin is Appropriate
Cephalexin is the oral agent of choice for non-purulent cellulitis without systemic signs of infection caused by MSSA or Streptococcus. 1, 2
- Indicated for impetigo caused by Staphylococcus and Streptococcus species 1
- Appropriate for penicillin-allergic patients except those with immediate hypersensitivity reactions 1, 2
- Offers advantages over dicloxacillin due to suspension availability and less frequent dosing requirements 2
Critical Caveat: When NOT to Use Cephalexin
Do not use cephalexin for suspected MRSA infections. 1, 2
Empiric MRSA coverage is required for patients with:
- Purulent drainage or abscesses 1
- Systemic inflammatory response syndrome (SIRS): fever >38°C or <36°C, tachycardia >90 bpm, tachypnea >24 breaths/min, WBC >12,000 or <4,000 cells/µL 1
- History of MRSA colonization 2
- Injection drug use 2
- Failed initial antibiotic therapy 1, 2
For these patients, use trimethoprim-sulfamethoxazole (1-2 double-strength tablets twice daily), doxycycline (100 mg twice daily), or clindamycin (300-450 mg four times daily) instead 1, 2
Important Clinical Context
For simple abscesses with adequate incision and drainage, antibiotics may not be necessary at all. 4 A randomized controlled trial showed 90.5% cure rates with drainage alone versus 84.1% with drainage plus cephalexin in MRSA-predominant abscesses 4. However, antibiotics are recommended for patients with:
- Carbuncles or abscesses with failed initial treatment 1
- Markedly impaired host defenses 1
- SIRS and hypotension 1
Necrotizing infections require immediate surgical intervention and broad-spectrum IV antibiotics—never use oral cephalexin for these life-threatening conditions. 2 Warning signs include severe pain disproportionate to findings, failure to respond to initial antibiotics, hard "woody" subcutaneous tissue, systemic toxicity, crepitus, bullae, or skin necrosis 1