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 dosing of 15-20 mg/kg IV every 8-12 hours and target trough concentrations of 15-20 μg/mL for severe infections. 1

First-Line Treatment Options by Infection Type

Skin and Soft Tissue Infections (SSTIs)

• For simple abscesses or boils, incision and drainage may be adequate 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 <10%) 1, 2
  • Doxycycline 100 mg twice daily 1, 2
  • Linezolid 600 mg twice daily 1, 2
• For severe or complicated SSTIs requiring IV therapy:
  • Vancomycin 15-20 mg/kg IV every 8-12 hours 3, 1
  • Linezolid 600 mg IV/PO twice daily 3, 4
  • Daptomycin 4-6 mg/kg IV daily (not for pneumonia) 1, 5

Pneumonia

• Vancomycin 15-20 mg/kg IV every 8-12 hours with target trough concentrations of 15-20 μg/mL 1, 6
• Linezolid 600 mg IV/PO twice daily (may be superior to vancomycin for MRSA pneumonia) 1, 7
• Avoid daptomycin for pneumonia due to inactivation by pulmonary surfactant 1

Bacteremia and Endocarditis

• Vancomycin 15-20 mg/kg IV every 8-12 hours with target trough concentrations of 15-20 μg/mL 3
• For persistent MRSA bacteremia or vancomycin treatment failure:
  • High-dose daptomycin (10 mg/kg/day) in combination with another agent such as gentamicin, rifampin, linezolid, TMP-SMX, or a beta-lactam 3
  • Daptomycin has shown non-inferiority to vancomycin in MRSA bacteremia 7

CNS Infections (Brain abscess, Subdural empyema, Spinal epidural abscess)

• IV vancomycin for 4-6 weeks 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 SSTIs with normal renal function:
  • Traditional doses of 1 g every 12 hours may be adequate 3, 1
  • Trough monitoring not required for these cases 3
• Trough monitoring is recommended for:
  • Serious infections 3
  • Morbidly obese patients 3
  • Patients with renal dysfunction 3
  • Patients with fluctuating volumes of distribution 3

Alternative Agents for MRSA

• Linezolid 600 mg PO/IV twice daily 1, 4
  • Particularly effective for pneumonia and skin infections 1
  • Cure rates for MRSA SSTIs comparable to vancomycin (79% vs 73%) 4
• Daptomycin 4-6 mg/kg IV daily (not for pneumonia) 1, 5
  • Effective for bacteremia and SSTIs 5
• TMP-SMX 1-2 double-strength tablets PO twice daily or 5 mg/kg IV twice daily 1, 2
• Clindamycin 300-450 mg PO three times daily or 600-900 mg IV three times daily 1, 2
• Doxycycline/minocycline 100 mg PO twice daily 1, 2

Special Considerations

• For vancomycin MIC ≥2 μg/mL (VISA or VRSA), use an alternative to vancomycin 3, 1
• For persistent MRSA bacteremia despite adequate therapy:
  • Search for and remove other foci of infection 3
  • Consider alternative agents regardless of MIC 1
• In critically ill trauma patients with MRSA pneumonia, vancomycin doses of at least 1 g IV every 8 hours are needed to achieve target trough concentrations 8

Pediatric Considerations

• Vancomycin 15 mg/kg/dose IV every 6 hours 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

• Inadequate vancomycin dosing leading to subtherapeutic levels, especially in critically ill patients 8
• Using daptomycin for MRSA pneumonia (contraindicated due to inactivation by pulmonary surfactant) 1
• 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
• Inadequate duration of therapy, especially for deep-seated infections 3