Initial Antibiotic Selection for Pneumonia
The initial empirical antibiotic choice for pneumonia should be based on the severity of illness, treatment setting, and risk factors for specific pathogens, with a non-antipseudomonal cephalosporin plus a macrolide or a respiratory fluoroquinolone being the preferred regimen for hospitalized non-ICU patients with community-acquired pneumonia. 1
Classification and Risk Assessment
Treatment selection depends on:
Pneumonia classification:
- Community-acquired pneumonia (CAP)
- Hospital-acquired pneumonia (HAP)
- Healthcare-associated pneumonia (HCAP)
- Aspiration pneumonia
Severity assessment:
- Mild (outpatient)
- Moderate (hospital ward)
- Severe (ICU)
Risk factors for resistant organisms:
- Recent antibiotic use
- Healthcare exposure
- Immunosuppression
- Risk for Pseudomonas aeruginosa
Empiric Antibiotic Regimens by Setting
Outpatient Treatment
Healthy adults without comorbidities:
- Amoxicillin
- Doxycycline
- Macrolide (in areas with low pneumococcal resistance)
Adults with comorbidities:
- Amoxicillin/clavulanate ± macrolide
- Respiratory fluoroquinolone (levofloxacin or moxifloxacin)
Non-ICU Hospitalized Patients
- Standard regimen (in alphabetical order) 1:
- Aminopenicillin ± macrolide
- Aminopenicillin/β-lactamase inhibitor ± macrolide
- Non-antipseudomonal cephalosporin (cefotaxime or ceftriaxone) ± macrolide
- Respiratory fluoroquinolone (levofloxacin or moxifloxacin)
- Penicillin G ± macrolide
ICU Hospitalized Patients
Without Pseudomonas risk factors 1:
- Non-antipseudomonal cephalosporin III + macrolide
- OR moxifloxacin or levofloxacin ± non-antipseudomonal cephalosporin III
With Pseudomonas risk factors 1:
- Antipseudomonal cephalosporin OR acylureidopenicillin/β-lactamase inhibitor OR carbapenem (meropenem preferred)
- PLUS ciprofloxacin OR macrolide + aminoglycoside
Aspiration Pneumonia
- Preferred regimen 2:
- Amoxicillin/clavulanate (1-2 g PO q12h)
- Alternative: moxifloxacin (400 mg PO daily) for penicillin allergies
- IV options: piperacillin/tazobactam, ertapenem, or levofloxacin
Nosocomial Pneumonia
- Initial treatment 3:
- Piperacillin/tazobactam 4.5 g IV every 6 hours plus an aminoglycoside
Pathogen-Specific Considerations
Atypical Pathogens
Chlamydophila pneumoniae 1:
- Doxycycline, macrolide, levofloxacin, or moxifloxacin
Legionella spp. 1:
- Levofloxacin (preferred)
- Moxifloxacin
- Macrolide (azithromycin preferred) ± rifampicin
Resistant Organisms
MRSA 2:
- Add vancomycin or linezolid
Pseudomonas aeruginosa 1:
- Antipseudomonal cephalosporin, acylureidopenicillin/β-lactamase inhibitor, or carbapenem
- PLUS ciprofloxacin OR aminoglycoside + macrolide
Treatment Duration and Monitoring
- Standard duration: Generally not exceeding 8 days in responding patients 1, 2
- Clinical response assessment: Within 48-72 hours of initiating therapy 2
- Clinical stability criteria 2:
- Temperature ≤37.8°C for 48 hours
- Heart rate ≤100 beats/min
- Respiratory rate ≤24 breaths/min
- Systolic BP ≥90 mmHg
- Oxygen saturation ≥90%
Important Caveats
- Timing: Antibiotic treatment should be initiated immediately after diagnosis of CAP 1
- De-escalation: Once a specific pathogen is identified, therapy should be narrowed to target that organism 2
- Antimicrobial stewardship: Choose the narrowest-spectrum agent to which the organism is susceptible 2
- Local resistance patterns: Consider local antibiotic resistance patterns when selecting empiric therapy 2
- Multidrug resistance: Recent research indicates increasing multidrug resistance in CAP pathogens, particularly with S. pneumoniae, K. pneumoniae, and P. aeruginosa 4
Evidence-Based Insights
- Beta-lactam monotherapy has been shown to be non-inferior to beta-lactam-macrolide combination or fluoroquinolone monotherapy for non-ICU hospitalized CAP patients regarding 90-day mortality 5
- Healthcare-associated pneumonia (HCAP) patients more frequently receive inappropriate initial empirical antibiotic therapy (5.6% vs 2.0%) and have higher case-fatality rates (10.3% vs 4.3%) compared to CAP patients 6