Initial Treatment for Hospital-Acquired Pneumonia
For hospital-acquired pneumonia, initiate empiric therapy with an antipseudomonal beta-lactam (piperacillin-tazobactam 4.5g IV q6h, cefepime 2g IV q8h, meropenem 1g IV q8h, or imipenem 500mg IV q6h), adding MRSA coverage with vancomycin or linezolid if risk factors are present, and using combination therapy with two antipseudomonal agents for high-risk patients. 1, 2
Risk Stratification Determines Antibiotic Selection
The first critical step is determining whether the patient has risk factors for multidrug-resistant (MDR) pathogens or high mortality risk, as this dictates the breadth of empiric coverage needed. 1, 2
Low-Risk HAP (Narrow-Spectrum Monotherapy)
Use narrow-spectrum monotherapy only if the patient meets ALL of the following criteria: 2, 3
- Early-onset HAP (<5 days hospitalization) 2, 3
- No prior IV antibiotic use within 90 days 1, 2, 3
- No septic shock or need for ventilatory support 1, 3
- Local ICU MRSA prevalence <20% 1, 3
- No prior MDR colonization 3
Acceptable monotherapy options: 1, 3
- Piperacillin-tazobactam 4.5g IV q6h
- Cefepime 2g IV q8h
- Levofloxacin 750mg IV daily
- Imipenem 500mg IV q6h
- Meropenem 1g IV q8h
High-Risk HAP (Broad-Spectrum Combination Therapy)
Patients require broad-spectrum coverage if they have any of these risk factors: 1, 2, 4
- Prior IV antibiotic use within 90 days 1, 2, 4
- Hospitalization >5 days 2, 4, 3
- Septic shock or need for mechanical ventilation 1, 2, 4
- Local ICU MRSA prevalence >20% or unknown 1, 3
- Prior MDR pathogen colonization 2, 3
Empiric Regimen Components
Antipseudomonal Beta-Lactam (Mandatory for All HAP)
All empiric HAP regimens must include coverage for Pseudomonas aeruginosa and gram-negative bacilli. 1, 2, 4 Choose one: 1, 5
- Piperacillin-tazobactam 4.5g IV q6h (most commonly used) 1, 5, 6
- Cefepime 2g IV q8h 1
- Meropenem 1g IV q8h 1
- Imipenem 500mg IV q6h 1
Ceftriaxone is not appropriate for HAP because it lacks adequate Pseudomonas coverage. 4
MRSA Coverage (Add When Risk Factors Present)
Add MRSA coverage if the patient has: 1, 2
- Prior IV antibiotic use within 90 days 1, 2
- Hospitalization in a unit where >20% of S. aureus isolates are methicillin-resistant or prevalence unknown 1, 2
- High mortality risk (septic shock or ventilatory support due to HAP) 1, 2
- Vancomycin 15 mg/kg IV q8-12h (target trough 15-20 mg/mL; consider loading dose 25-30 mg/kg for severe illness) 1, 3
- Linezolid 600mg IV q12h 1, 3
Combination Therapy for Pseudomonas (High-Risk Patients Only)
For patients with prior IV antibiotics within 90 days, structural lung disease, or high mortality risk, use two different antibiotic classes active against Pseudomonas: 1, 2, 7
Antipseudomonal beta-lactam PLUS one of: 1
- Levofloxacin 750mg IV daily or ciprofloxacin 400mg IV q8h 1
- Aminoglycoside: amikacin 15-20 mg/kg IV daily, gentamicin 5-7 mg/kg IV daily, or tobramycin 5-7 mg/kg IV daily 1
- Aztreonam 2g IV q8h (if severe penicillin allergy) 1
Critical pitfall: Never use two beta-lactams together. 1 Monotherapy for pseudomonal HAP is associated with rapid resistance development and high clinical failure rates. 7
Administration and Monitoring
- Administer all antibiotics by IV infusion over 30 minutes 5
- Obtain lower respiratory tract cultures before initiating antibiotics to guide de-escalation 4, 3
- Reassess at 48-72 hours using clinical response, culture results, and antimicrobial susceptibilities 3
- De-escalate to narrower therapy by day 3 based on culture results 2, 3
- Treat for 7-8 days if good clinical response and no complications 2, 3
Common Pitfalls to Avoid
- Do not use ceftriaxone for empiric HAP—it lacks Pseudomonas coverage 4
- Do not use aminoglycosides as the sole antipseudomonal agent 4
- Do not assume community-acquired pneumonia regimens work for HAP 4
- Do not use two beta-lactams together in combination therapy 1
- Use ICU-specific antibiograms, not hospital-wide resistance data, to guide empiric choices 3