Treatment of MRSA Lung Infection
For confirmed or suspected MRSA pneumonia, use either vancomycin 15 mg/kg IV every 8-12 hours (targeting trough levels of 15-20 mg/mL) or linezolid 600 mg IV/PO twice daily as first-line therapy. 1
Risk Stratification and Empiric Coverage Decision
The decision to initiate empiric MRSA coverage depends on specific risk factors:
Indications for Empiric MRSA Coverage 1
- Prior IV antibiotic use within 90 days
- Hospitalization in a unit where >20% of S. aureus isolates are methicillin-resistant (or prevalence unknown)
- High risk of mortality, defined as:
- Need for ventilatory support due to pneumonia
- Septic shock
Patients NOT Requiring Empiric MRSA Coverage 1
If the patient has no risk factors for MRSA and is not at high risk of mortality, empiric coverage should target MSSA only with agents such as piperacillin-tazobactam, cefepime, levofloxacin, imipenem, or meropenem. 1
First-Line Antibiotic Selection
Vancomycin Dosing 1
- Standard dose: 15 mg/kg IV every 8-12 hours
- Target trough level: 15-20 mg/mL
- Loading dose: Consider 25-30 mg/kg IV × 1 for severe illness 1
- Critical consideration: Standard dosing of 1 g IV every 12 hours is inadequate for critically ill patients and unlikely to achieve therapeutic trough levels 2. Doses of at least 1 g IV every 8 hours are needed in critically ill trauma patients with normal renal function. 2
Linezolid as Alternative 1
- Dose: 600 mg IV or PO twice daily
- Advantages: May be superior to vancomycin specifically for hospital-acquired pneumonia 3, 4
- Duration: 7-21 days depending on extent of infection 1
Clindamycin (If Susceptible) 1
- Dose: 600 mg IV/PO three times daily
- Critical caveat: Only use if local clindamycin resistance rate is low (e.g., <10%) 1
- Should NOT be used if there is concern for endovascular infection 1
Combination Therapy Considerations
When to Add Gram-Negative Coverage 1
For patients with high risk of mortality or prior IV antibiotic use within 90 days, add coverage for Pseudomonas and gram-negative bacilli using two agents from different classes (avoid two β-lactams): 1
- Antipseudomonal β-lactam (piperacillin-tazobactam 4.5 g IV q6h, cefepime 2 g IV q8h, or carbapenem)
- PLUS fluoroquinolone (levofloxacin 750 mg IV daily) or aminoglycoside (gentamicin 5-7 mg/kg IV daily)
Structural Lung Disease 1
Patients with bronchiectasis or cystic fibrosis require two antipseudomonal agents due to increased risk of gram-negative infection. 1
Duration of Therapy
7-21 days depending on the extent of infection and clinical response 1
Special Considerations and Common Pitfalls
Vancomycin Limitations 5, 3, 4
- Emergence of less-susceptible strains with poor clinical outcomes
- Increased nephrotoxicity with high-dose therapy
- Many strains have MICs that make achieving adequate PK/PD targets difficult
- Vancomycin should be used with caution in severe life-threatening disease 4
Daptomycin Should NOT Be Used 5
Daptomycin is contraindicated for MRSA pneumonia despite its efficacy in bacteremia and endocarditis, as it is inactivated by pulmonary surfactant. 5
Empyema Management 1
If MRSA pneumonia is complicated by empyema, antimicrobial therapy must be used in conjunction with drainage procedures. 1
De-escalation Strategy 1
Base empiric regimens on local antibiograms and antimicrobial susceptibilities. 1 Once cultures return, narrow therapy appropriately to avoid unnecessary broad-spectrum coverage.