What are the criteria for treating hospital-acquired pneumonia (HAP)?

Hospital-Acquired Pneumonia Treatment Criteria

Empiric antibiotic selection for hospital-acquired pneumonia must be based on risk stratification for multidrug-resistant (MDR) pathogens and septic shock, with low-risk patients receiving narrow-spectrum monotherapy and high-risk patients requiring broad-spectrum combination therapy targeting Pseudomonas aeruginosa, ESBL-producing organisms, and MRSA. 1, 2

Risk Stratification Framework

Low-Risk Patients (Narrow-Spectrum Monotherapy)

Low-risk patients are defined by all of the following criteria 1, 2, 3:

• Early-onset HAP (within first 4-5 days of hospitalization) 1, 3
• No prior intravenous antibiotic use within 90 days 1, 2, 3
• No septic shock or need for ventilatory support 1, 2
• Local ICU resistance rates <25% for MDR pathogens 1, 2, 3
• No previous colonization with MDR organisms 2, 3
• No structural lung disease (bronchiectasis, cystic fibrosis) 1, 4

High-Risk Patients (Broad-Spectrum Combination Therapy)

High-risk patients have any of the following 1, 2, 3:

• Septic shock or need for ventilatory support due to HAP 1, 2, 4
• Prior intravenous antibiotic use within 90 days 1, 2, 3, 4
• Prolonged hospitalization (>5 days) 1, 2, 3, 4
• Local ICU resistance rates >25% for MDR pathogens 1, 2, 3
• Previous colonization with MDR organisms 2, 3, 4
• Hospitalization in a unit where >20% of S. aureus isolates are methicillin-resistant or MRSA prevalence unknown 1, 4
• Structural lung disease (bronchiectasis, cystic fibrosis) 1, 4

Critical caveat: The relevant resistance rate is the ICU-specific rate where the patient is being treated, not the hospital-wide rate 1, 2, 3.

Empiric Antibiotic Regimens

For Low-Risk Patients

Use monotherapy with one of the following 1, 2, 3:

• Ertapenem (dose not specified in guidelines) 1, 2, 3
• Ceftriaxone 1-2 g IV daily OR cefotaxime 1-2 g IV q8h 1, 2, 3
• Levofloxacin 750 mg IV daily OR moxifloxacin 400 mg IV daily 1, 2, 3

Important warning: Third-generation cephalosporins (ceftriaxone, cefotaxime) carry higher risk of Clostridioides difficile infection compared to penicillins or quinolones 1, 2.

For High-Risk Patients Without Septic Shock

Use an antipseudomonal beta-lactam 1, 2, 3:

• Piperacillin-tazobactam 4.5 g IV q6h 1, 2, 3, 4
• Cefepime 2 g IV q8h 1, 2, 3, 4
• Ceftazidime 2 g IV q8h 1, 2, 3, 4
• Meropenem 1 g IV q8h 1, 2, 3, 4
• Imipenem 500 mg IV q6h 1, 2, 3, 4

For High-Risk Patients With Septic Shock or Structural Lung Disease

Use combination therapy with two antipseudomonal agents from different classes 1, 2:

• Antipseudomonal beta-lactam (as above) PLUS one of the following 1, 2:
  • Levofloxacin 750 mg IV daily OR ciprofloxacin 400 mg IV q8h 1, 2
  • Amikacin 15-20 mg/kg IV daily OR gentamicin 5-7 mg/kg IV daily OR tobramycin 5-7 mg/kg IV daily 1, 2
  • Aztreonam 2 g IV q8h 1, 2

Avoid using two beta-lactams together 1.

MRSA Coverage

Add MRSA coverage for high-risk patients with 1, 2, 3, 4:

• Prior IV antibiotic use within 90 days 1, 4
• Hospitalization in unit where >20% of S. aureus isolates are MRSA 1, 4
• High risk of mortality (septic shock, ventilatory support) 1, 4

MRSA treatment options 1, 2, 3, 4:

• Vancomycin 15 mg/kg IV q8-12h (target trough 15-20 mg/mL; consider loading dose 25-30 mg/kg for severe illness) 1, 2, 4
• Linezolid 600 mg IV q12h 1, 2, 3, 4

Microbiological Sampling Strategy

Obtain lower respiratory tract samples BEFORE initiating antibiotics to enable subsequent de-escalation 1, 2, 3, 4. Acceptable methods include 1, 2, 3:

• Distal quantitative samples (preferred in stable patients to reduce antibiotic exposure) 1, 2
• Proximal quantitative samples 1, 3
• Qualitative cultures 1, 3

Do not delay antibiotics in critically ill patients while awaiting sampling 3.

De-escalation and Duration

Reassessment at Day 3

Tailor therapy to culture susceptibilities by day 3 based on 2, 3, 4:

• Temperature trends 2
• White blood cell count 2
• Chest radiography 2
• Oxygenation parameters 2
• Hemodynamic stability 2

De-escalate from combination to monotherapy once cultures identify susceptible organisms, unless treating extensively drug-resistant (XDR) or pandrug-resistant (PDR) nonfermenting gram-negatives or carbapenem-resistant Enterobacteriaceae 1, 2, 3.

Treatment Duration

Treat for 7-8 days in patients with 2, 3, 4:

• Good clinical response 2, 3, 4
• No immunodeficiency 2, 3
• No complications (lung abscess, empyema, cavitation, necrotizing pneumonia) 2, 3

Longer courses (14 days) may be necessary for 3, 4:

• Immunocompromised patients 3
• Complications (lung abscess, empyema, necrotizing pneumonia) 3
• Inadequate initial empiric therapy 3

Common Pitfalls

Local antibiograms are mandatory for guiding empiric therapy—resistance patterns vary significantly between hospitals and ICUs 1, 2, 3. The institution should regularly generate and disseminate ICU-specific antibiograms 1.

Inappropriate initial therapy increases mortality, so ensuring adequate empiric coverage for likely pathogens based on local resistance patterns is crucial 3.

Negative culture results are most reliable when obtained before antibiotics or within 72 hours of antibiotic changes 2.