Coverage of Pseudomonas aeruginosa by Cefepime and Vancomycin
Cefepime provides excellent coverage against Pseudomonas aeruginosa, but vancomycin has no antipseudomonal activity whatsoever. 1, 2
Cefepime Coverage for Pseudomonas
Cefepime is a highly effective antipseudomonal agent and is FDA-approved specifically for treating Pseudomonas aeruginosa infections, including pneumonia. 2 The drug demonstrates:
- Broad-spectrum activity against P. aeruginosa comparable to ceftazidime, with susceptibility rates of 67-83% across geographic regions 3
- Superior stability against AmpC beta-lactamases compared to third-generation cephalosporins, making it effective against organisms resistant to ceftazidime 4
- Recommended dosing of 2g IV every 8-12 hours for Pseudomonas infections, with higher doses (2g every 8 hours) specifically indicated for P. aeruginosa pneumonia 2, 5
Pharmacodynamic Requirements
For optimal microbiological response against P. aeruginosa, cefepime must achieve >60% fT>MIC (time above MIC) 5. Patients with exposures ≤60% fT>MIC are 8.1 times more likely to experience treatment failure 5. This target requires:
- At least 2g every 8 hours in patients with normal renal function when treating CLSI-susceptible P. aeruginosa 5
- Continuous infusion may optimize bactericidal activity by maintaining concentrations above MIC throughout the dosing interval 6
Vancomycin Coverage for Pseudomonas
Vancomycin provides zero coverage against Pseudomonas aeruginosa. 1 Vancomycin is a glycopeptide antibiotic that:
- Only covers Gram-positive organisms, particularly methicillin-resistant Staphylococcus aureus (MRSA) 7
- Has no activity against Gram-negative bacteria including all Pseudomonas species 1
- Should only be added to empiric regimens when MRSA prevalence exceeds 25% in the ICU setting 7
Clinical Implications for Combination Therapy
When cefepime and vancomycin are used together empirically:
- Cefepime alone provides the Pseudomonas coverage in this combination 1, 2
- Vancomycin adds only MRSA coverage, which may be appropriate for severe hospital-acquired or ventilator-associated pneumonia where both pathogens are concerns 7
- For critically ill patients with suspected Pseudomonas, consider adding a second antipseudomonal agent (aminoglycoside or fluoroquinolone) rather than relying on vancomycin for additional coverage 7, 1
Monotherapy vs. Combination Considerations
Cefepime monotherapy is generally preferred for susceptible P. aeruginosa infections 7, 1. However, combination therapy with a second antipseudomonal agent (not vancomycin) should be considered when:
- Septic shock is present 7
- Multidrug-resistant P. aeruginosa is suspected (prior IV antibiotic use within 90 days, prolonged hospitalization) 1
- Local resistance rates exceed 10-20% 1
- Critically ill patients with ventilator-associated pneumonia 7
Common Pitfalls to Avoid
- Do not assume vancomycin contributes to Pseudomonas coverage - it provides only Gram-positive coverage 1
- Avoid cefepime monotherapy in institutions with high rates of resistance or when treating critically ill patients with risk factors for MDR organisms 7, 1
- Do not use inadequate cefepime dosing - doses of 1g every 12 hours may be insufficient for P. aeruginosa; use at least 2g every 8-12 hours 2, 5
- Never use aminoglycoside monotherapy for Pseudomonas bacteremia due to rapid resistance emergence 1