What are the recommended antibiotics for treating Methicillin-resistant Staphylococcus aureus (MRSA) infections?

Recommended Antibiotics for MRSA Infections

Vancomycin is the first-line treatment for most serious MRSA infections, with a dosing regimen of 15-20 mg/kg/dose IV every 8-12 hours based on actual body weight, targeting trough concentrations of 15-20 μg/mL for serious infections. 1

Treatment by Infection Type

Skin and Soft Tissue Infections

• For simple abscesses or boils, incision and drainage alone may be sufficient without antibiotics 2
• For purulent cellulitis, recommended oral options include:
  • Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets twice daily 1, 2
  • Clindamycin 300-450 mg three times daily (if local resistance rates <10%) 1, 2
  • Doxycycline 100 mg twice daily 1, 2
  • Linezolid 600 mg twice daily 1, 2
• For severe skin infections requiring IV therapy, vancomycin 15-20 mg/kg/dose every 8-12 hours is recommended 3, 1

Bacteremia and Endocarditis

• Vancomycin is the first-line agent, dosed at 15-20 mg/kg/dose every 8-12 hours with target trough concentrations of 15-20 μg/mL 3, 1
• For persistent MRSA bacteremia or vancomycin treatment failures:
  • High-dose daptomycin (10 mg/kg/day) in combination with another agent (gentamicin, rifampin, linezolid, or TMP-SMX) should be considered 3
  • Daptomycin has shown non-inferiority to vancomycin in MRSA bacteremia treatment 4

Pneumonia

• Linezolid 600 mg PO/IV twice daily is preferred for MRSA pneumonia 1, 5
• Vancomycin can be used but requires higher dosing to achieve adequate lung penetration 6
• Daptomycin should not be used for pneumonia due to inactivation by pulmonary surfactant 1

Central Nervous System Infections

• For brain abscess, subdural empyema, or spinal epidural abscess:
  • Neurosurgical evaluation for incision and drainage is recommended 3
  • IV vancomycin for 4-6 weeks is recommended 3
  • Some experts recommend adding rifampin 600 mg daily or 300-450 mg twice daily 3
  • Alternatives include linezolid 600 mg PO/IV twice daily or TMP-SMX 5 mg/kg/dose IV every 8-12 hours 3

Vancomycin Dosing and Monitoring

• Initial dosing: 15-20 mg/kg/dose (actual body weight) every 8-12 hours, not to exceed 2 g per dose 3, 1
• For serious infections (bacteremia, endocarditis, osteomyelitis, meningitis, pneumonia, severe SSTI):
  • Target trough concentrations of 15-20 μg/mL 3, 1
  • Consider a loading dose of 25-30 mg/kg in critically ill patients 3
• For less severe skin infections with normal renal function:
  • Traditional doses of 1 g every 12 hours may be adequate without trough monitoring 3, 1
• Trough monitoring is recommended for:
  • Serious infections 3
  • Morbidly obese patients 3
  • Patients with renal dysfunction 3
  • Patients with fluctuating volume of distribution 3

Alternative Agents for MRSA

• Linezolid 600 mg PO/IV twice daily:
  • Particularly effective for pneumonia and skin infections 1
  • May be superior to vancomycin for hospital-acquired pneumonia 4
  • Has shown higher clinical success rates than vancomycin in recent studies 5
• Daptomycin 4-6 mg/kg/day IV:
  • Alternative for bacteremia and skin infections 1
  • Not for pneumonia due to inactivation by pulmonary surfactant 1
  • Has demonstrated non-inferiority to vancomycin in bacteremia 7, 4
• TMP-SMX:
  • Effective for skin and soft tissue infections 1, 2
• Clindamycin:
  • Option for skin and soft tissue infections if local resistance rates are low 1, 2

Special Considerations

• For vancomycin MIC ≥2 μg/mL (VISA or VRSA), an alternative to vancomycin should be used 3, 1
• For persistent MRSA bacteremia despite adequate vancomycin therapy, consider alternative agents regardless of MIC 3, 1
• Tissue penetration of vancomycin may be reduced in patients with decreased vascular perfusion, such as those with lower-limb infections 8
• Combination therapy with vancomycin plus rifampin has shown better clinical success rates than vancomycin alone in some studies 5

Pediatric Considerations

• Vancomycin 15 mg/kg/dose IV every 6 hours is recommended for serious infections 3, 1
• Clindamycin 10-13 mg/kg/dose IV every 6-8 hours, not to exceed 40 mg/kg/day 1
• Linezolid 10 mg/kg/dose every 8 hours for children <12 years 2

Common Pitfalls to Avoid

• Underdosing vancomycin in critically ill patients - traditional dosing of 1 g every 12 hours is unlikely to achieve target trough concentrations of 15-20 mg/mL 6
• Failure to perform adequate incision and drainage of abscesses, which is essential for successful treatment 2
• Not considering local resistance patterns when selecting empiric therapy 2
• Using daptomycin for pneumonia, where it is ineffective due to inactivation by pulmonary surfactant 1