Is Keflex (cefalexin) appropriate for a patient with a wound culture positive for moderate Staphylococcus aureus?

Treatment of Wound Infection with Staphylococcus aureus

Cephalexin (Keflex) is an appropriate first-line treatment for a wound culture positive for moderate Staphylococcus aureus, especially if it is methicillin-susceptible S. aureus (MSSA). 1

Rationale for Using Cephalexin

Cephalexin is specifically FDA-approved for skin and skin structure infections caused by Staphylococcus aureus and/or Streptococcus pyogenes 1. The Infectious Diseases Society of America (IDSA) guidelines support this choice:

• For non-purulent skin infections (such as typical wound infections), cephalexin is recommended as a first-choice antibiotic 2
• For MSSA infections, first-generation cephalosporins like cephalexin are appropriate treatment options 3
• The WHO's Essential Medicines List also includes cephalexin as a first-choice antibiotic for mild skin and soft tissue infections 2

Treatment Algorithm

1. Confirm the type of infection:

   • If the wound shows moderate S. aureus without purulent drainage → Cephalexin is appropriate
   • If the wound has purulent drainage or abscess → Consider incision and drainage plus antibiotics

2. Antibiotic selection based on susceptibility:

   • For MSSA: Cephalexin 500 mg orally four times daily for 5-10 days 2
   • For suspected or confirmed MRSA: Switch to alternative agents:
     • Clindamycin
     • Trimethoprim-sulfamethoxazole (TMP-SMX)
     • Doxycycline
     • Linezolid

3. Monitor for clinical response:

   • Improvement should be seen within 48-72 hours
   • If no improvement, reassess for:
     • Possible MRSA (consider changing antibiotics)
     • Need for drainage if abscess has formed
     • Deeper infection requiring more aggressive management

Dosing and Duration

• Standard adult dose: Cephalexin 500 mg orally four times daily 4
• Duration: 5-10 days, based on clinical response 2
• Alternative dosing: Some studies suggest twice-daily dosing may be effective for better compliance 5, 6

Important Considerations and Caveats

1. Culture results matter:

   • The culture has already confirmed S. aureus, but susceptibility testing should guide therapy if available 2
   • If MRSA is suspected or confirmed, cephalexin will not be effective 2

2. Incision and drainage:

   • For any abscess formation, incision and drainage is the primary treatment 2
   • For simple abscesses, some evidence suggests that drainage alone without antibiotics may be sufficient 4

3. When to consider alternative antibiotics:

   • Patient allergic to beta-lactams
   • No clinical improvement after 48-72 hours of cephalexin
   • Confirmed MRSA infection
   • Severe infection with systemic symptoms

4. Prevention of recurrence:

   • Keep wounds covered with clean, dry bandages
   • Maintain good personal hygiene
   • For recurrent infections, consider decolonization strategies 2

Cephalexin has demonstrated high cure rates (90% or higher) for staphylococcal skin infections over many years of clinical use 5. It remains effective against MSSA and has comparable in vitro activity to other first-generation cephalosporins 7.