Management of Community-Acquired Pneumonia due to Methicillin-Resistant Staphylococcus aureus (CAP-MRSA)
Add vancomycin or linezolid to your standard CAP regimen when CA-MRSA is suspected or confirmed. 1
When to Suspect CA-MRSA
CA-MRSA pneumonia should be considered in specific clinical scenarios that differ from typical CAP presentations:
- Young, previously healthy individuals presenting with rapidly progressive, severe pneumonia 2
- Necrotizing features on imaging, including cavitary consolidation, bilateral infiltrates, or lung necrosis 3, 2
- Hemoptysis as a presenting symptom 4, 2
- Pleural effusions developing early in the hospital course 3
- Post-influenza pneumonia, though this is NOT always present—many cases occur without preceding influenza 3, 2
- Leukopenia accompanying severe pneumonia 5
- Septic shock in previously healthy adults 4
Antibiotic Selection
First-Line Agents
Vancomycin or linezolid are the recommended antibiotics for CA-MRSA pneumonia. 1, 6
- Both agents inhibit bacterial exotoxin production, which may improve outcomes in CA-MRSA pneumonia 3
- Linezolid has been associated with improved survival in some observational studies, though vancomycin remains widely used 3
Vancomycin Dosing Considerations
Standard vancomycin dosing of 1 gram IV every 12 hours is inadequate for critically ill patients with MRSA pneumonia. 7
- Target trough concentrations of 15-20 mg/L are recommended for MRSA pneumonia 7
- In critically ill trauma patients with normal renal function, at least 1 gram IV every 8 hours is needed to achieve therapeutic troughs 7
- Only 23.5% of patients receiving 1 gram every 8 hours achieved target troughs >15 mg/L, while NONE receiving every 12 hour dosing achieved this target 7
Combination Therapy
CA-MRSA treatment should be added to—not replace—your standard severe CAP regimen. 1, 6
The standard severe CAP regimen consists of:
- A β-lactam (cefotaxime, ceftriaxone, or ampicillin-sulbactam) PLUS
- Either azithromycin or a respiratory fluoroquinolone 1
Then ADD vancomycin or linezolid when CA-MRSA is a consideration. 1, 6
Treatment Duration and Monitoring
- Treat for 14-21 days when staphylococcal pneumonia is confirmed, given the necrotizing nature of CA-MRSA infections 8
- Monitor for complications including pleural effusions requiring drainage (occurred in 5 of 9 patients with effusions in one series) 3
- Assess for lung necrosis with chest CT scanning, as this was present in 8 of 14 patients in one cohort 3
Special Populations
Immunocompromised patients have higher mortality from CA-MRSA pneumonia. 3
Risk factors for severe disease include:
- HIV/AIDS 3
- Active malignancy (especially hematologic) 3
- High-dose corticosteroid therapy 3
- Immunoglobulin deficiency 3
- Diabetes mellitus 3
Mortality in immunocompetent patients may be lower than historically reported (13% in one series), particularly when treated with toxin-inhibiting antibiotics 3
Critical Pitfalls to Avoid
- Do not assume influenza preceded the infection—only 1 of 14 patients in one series had evidence of preceding influenza 3
- Do not use standard vancomycin dosing—1 gram every 12 hours will fail to achieve therapeutic levels in critically ill patients 7
- Do not delay empiric coverage—CA-MRSA pneumonia progresses rapidly and early aggressive treatment is essential 2
- Do not assume ICU admission is always required—7 of 15 patients in one series were never admitted to the ICU, though close monitoring is warranted 3