Does Keflex (cephalexin) treat MESa?

Does Keflex (Cephalexin) Treat MRSA?

Keflex (cephalexin) is NOT effective against MRSA and should not be used for treating MRSA infections. According to current guidelines, cephalexin lacks activity against methicillin-resistant Staphylococcus aureus 1.

Antimicrobial Activity of Cephalexin

Cephalexin is a first-generation cephalosporin with the following spectrum of activity:

• Effective against:

  • Methicillin-susceptible Staphylococcus aureus (MSSA)
  • Streptococci (including Group A streptococci)
  • Some gram-negative organisms

• NOT effective against:

  • Methicillin-resistant Staphylococcus aureus (MRSA)
  • Extended-spectrum beta-lactamase (ESBL) producing organisms
  • Pseudomonas aeruginosa
  • Anaerobes

Recommended Antibiotics for MRSA

For suspected or confirmed MRSA infections, the following antibiotics are recommended instead of cephalexin 1:

Mild MRSA Infections:

• Trimethoprim-sulfamethoxazole
• Clindamycin
• Doxycycline
• Linezolid

Moderate to Severe MRSA Infections:

• Vancomycin
• Linezolid
• Daptomycin
• Teicoplanin

Clinical Applications of Cephalexin

Cephalexin is appropriately used for:

1. Skin and soft tissue infections caused by susceptible organisms (not MRSA):

   • Listed as a first-choice antibiotic for mild skin and soft tissue infections 1
   • Effective for streptococcal and methicillin-susceptible staphylococcal infections 2

2. Upper respiratory tract infections:

   • Effective for pharyngitis and tonsillitis due to beta-hemolytic streptococci 3
   • Comparable to penicillin for these indications

3. Diabetic wound infections (mild):

   • Listed as an option for mild diabetic wound infections (when MRSA is not suspected) 1

4. Incisional surgical site infections:

   • Recommended for surgical site infections after surgery of the trunk or extremities (away from axilla or perineum) 1

Common Pitfalls in MRSA Treatment

1. Misdiagnosis: Confusing cellulitis (which may respond to cephalexin) with MRSA infections (which will not)

2. Inadequate empiric coverage: Starting with cephalexin when MRSA is prevalent in your community

3. Delayed appropriate therapy: Continuing cephalexin despite clinical failure, which can lead to progression of infection

4. Failure to obtain cultures: Not identifying MRSA as the causative organism before selecting therapy

Special Considerations

1. Dose adjustment: Required for patients with creatinine clearance less than 30 ml/min 4, 5

2. Cross-reactivity: Up to 10% of penicillin-allergic patients may also be allergic to cephalosporins like cephalexin 4

3. Lyme disease: Cephalexin should not be used to treat Lyme disease as it has been shown to be ineffective 6

In conclusion, while cephalexin is an effective antibiotic for many common infections, it lacks activity against MRSA and should not be used when MRSA is suspected or confirmed as the causative pathogen.