What is the recommended treatment for Methicillin-resistant Staphylococcus aureus (MRSA) infections?

Treatment of Methicillin-Resistant Staphylococcus aureus (MRSA) Infections

Intravenous vancomycin is the recommended first-line therapy for serious MRSA infections, with dosing of 15-20 mg/kg every 8-12 hours and target trough concentrations of 15-20 μg/mL for severe infections. 1

Treatment Approach Based on Infection Type

Skin and Soft Tissue Infections (SSTIs)

• Uncomplicated SSTIs:

  • Incision and drainage is the primary treatment for purulent infections 2
  • Oral options:
    • Trimethoprim-sulfamethoxazole (TMP-SMX): 1-2 double-strength tablets (160mg/800mg) twice daily for 5-10 days 2
    • Clindamycin: 300-450 mg orally three times daily 1
    • Doxycycline or minocycline: 100 mg twice daily (not for children <8 years) 2
    • Linezolid: 600 mg orally twice daily (for severe cases) 1, 3

• Complicated SSTIs:

  • IV vancomycin 15-20 mg/kg every 8-12 hours (not to exceed 2g per dose) 1
  • Alternatives:
    • Linezolid 600 mg IV/PO twice daily (shown 90% cure rate in clinical trials) 3
    • Daptomycin 4-6 mg/kg IV once daily 4

Bacteremia and Endocarditis

• IV vancomycin for 2-6 weeks depending on complications 1
• For uncomplicated bacteremia: minimum 14 days therapy 1
• For complicated bacteremia or endocarditis: 4-6 weeks therapy 1
• Alternative options:
  • Daptomycin 6 mg/kg IV once daily (demonstrated non-inferiority to vancomycin in S. aureus bacteremia) 4, 5
  • Consider adding rifampin 600 mg daily or 300-450 mg twice daily in selected cases 1

Pneumonia

• IV vancomycin with loading dose of 25-30 mg/kg in seriously ill patients 1, 6
• Linezolid 600 mg IV/PO twice daily (may be superior to vancomycin for MRSA pneumonia) 1, 5

Central Nervous System Infections

• Meningitis: IV vancomycin for 2 weeks 1
• Brain abscess/epidural abscess: IV vancomycin for 4-6 weeks 1
• Neurosurgical drainage is recommended when applicable 1
• Alternatives: linezolid 600 mg PO/IV twice daily or TMP-SMX 5 mg/kg/dose IV every 8-12 hours 1

Vancomycin Dosing and Monitoring

Adult Dosing

• Standard dosing: 15-20 mg/kg/dose (actual body weight) every 8-12 hours 1
• Loading dose: 25-30 mg/kg for serious infections (sepsis, meningitis, pneumonia, endocarditis) 1
• For most SSTIs with normal renal function: 1 g every 12 hours 1

Monitoring

• Trough concentrations should be obtained before the 4th or 5th dose at steady state 1
• Target trough concentrations:
  • 15-20 μg/mL for serious infections (bacteremia, endocarditis, osteomyelitis, meningitis, pneumonia) 1, 7
  • 10-15 μg/mL for less severe infections 1
• AUC/MIC ratio ≥400 is the best predictor of efficacy 7, 8

Pediatric Dosing

• IV vancomycin 15 mg/kg/dose every 6 hours for serious infections 1
• Target trough concentrations of 15-20 μg/mL for serious infections 1

Treatment Failure Considerations

• For isolates with vancomycin MIC >2 μg/mL, use alternative agents 1
• If no clinical or microbiological response to vancomycin despite adequate debridement, switch to alternative agent regardless of MIC 1
• Consider surgical intervention for deep-seated infections 1

Special Considerations

• Pregnancy: Avoid TMP-SMX in third trimester 2
• Renal impairment: Adjust vancomycin dosing based on renal function 1
• Children <2 months: Avoid TMP-SMX 2
• Obese patients: Use actual body weight for initial dosing calculations 1

Prevention of MRSA Infections

• Standard precautions including hand hygiene
• Keep draining wounds covered with clean, dry bandages
• Avoid sharing personal items
• For recurrent infections, consider decolonization with mupirocin (nasal) and chlorhexidine (body) 2

Common Pitfalls to Avoid

1. Underdosing vancomycin: Traditional dosing of 1g every 12 hours often fails to achieve target trough concentrations, especially in critically ill patients 6, 9

2. Relying solely on MIC without considering AUC/MIC ratio: The therapeutic effectiveness of vancomycin is best described by AUC/MIC ratio rather than trough concentration alone 7, 8

3. Failure to obtain cultures before starting antibiotics: Culture results guide definitive therapy 2

4. Inadequate surgical intervention: Many treatment failures with deep-seated infections occur due to lack of necessary surgical intervention 1

5. Not adjusting therapy based on clinical response: If no improvement is seen despite adequate vancomycin therapy, consider alternative agents 1