PSI Score-Based Treatment for Community-Acquired Pneumonia
The PSI (Pneumonia Severity Index) score should guide site-of-care decisions, with risk classes I-III treated as outpatients and classes IV-V considered for hospitalization, followed by empiric antibiotic selection based on patient comorbidities and recent antibiotic exposure. 1
Using PSI to Determine Treatment Location
The IDSA recommends a 3-step process for initial site-of-care decisions: 1
- Step 1: Assess preexisting conditions that compromise safety of home care
- Step 2: Calculate the PSI score with recommendation for home care for risk classes I, II, and III
- Step 3: Apply clinical judgment to override the score when appropriate
This algorithmic approach prioritizes mortality reduction by ensuring high-risk patients receive hospital-level monitoring and care. 1
Outpatient Treatment (PSI Classes I-III)
Previously Healthy Patients Without Recent Antibiotics
For healthy outpatients, amoxicillin 1 gram three times daily is the preferred first-line therapy, with doxycycline 100 mg twice daily as an acceptable alternative. 2 A macrolide (azithromycin or clarithromycin) should only be used in areas where pneumococcal macrolide resistance is less than 25%. 2
Patients With Comorbidities or Recent Antibiotic Use
For outpatients with COPD, diabetes, renal failure, heart failure, or malignancy, the IDSA recommends: 1
- Without recent antibiotic therapy: An advanced macrolide (azithromycin or clarithromycin) OR a respiratory fluoroquinolone (levofloxacin, moxifloxacin, or gemifloxacin)
- With recent antibiotic therapy: A respiratory fluoroquinolone alone OR an advanced macrolide plus a β-lactam (amoxicillin-clavulanate, cefpodoxime, or cefuroxime)
This dual approach addresses both typical and atypical pathogens while accounting for resistance patterns. 2
Inpatient Treatment (PSI Classes IV-V, Medical Ward)
For hospitalized non-ICU patients, use either a β-lactam (ceftriaxone 1-2g daily, cefotaxime 1-2g every 8 hours, or ampicillin-sulbactam 3g every 6 hours) plus azithromycin 500mg daily, OR respiratory fluoroquinolone monotherapy (levofloxacin 750mg daily or moxifloxacin 400mg daily). 2 Both regimens carry strong recommendations with high-quality evidence. 2
The combination approach provides coverage for both typical bacterial pathogens (S. pneumoniae, H. influenzae) and atypical organisms (Mycoplasma, Legionella, Chlamydia). 1
Adjusting for Recent Antibiotic Exposure
If the patient received antibiotics recently, select the alternative regimen based on the prior antibiotic class to minimize resistance risk. 1
ICU Treatment (Severe PSI Class V)
Combination therapy is mandatory for all ICU patients: use a β-lactam (ceftriaxone 2g daily, cefotaxime 1-2g every 8 hours, or ampicillin-sulbactam 3g every 6 hours) PLUS either azithromycin 500mg daily OR a respiratory fluoroquinolone (levofloxacin 750mg daily or moxifloxacin 400mg daily). 2
When Pseudomonas Risk Factors Are Present
Add antipseudomonal coverage if the patient has: 2
- Structural lung disease (bronchiectasis)
- Recent hospitalization with IV antibiotics within 90 days
- Prior respiratory isolation of P. aeruginosa
Regimen: Antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) PLUS ciprofloxacin 400mg IV every 8 hours OR levofloxacin 750mg daily, PLUS an aminoglycoside (gentamicin 5-7 mg/kg daily or tobramycin 5-7 mg/kg daily). 2
When MRSA Risk Factors Are Present
Add MRSA coverage if the patient has: 2
- Post-influenza pneumonia
- Cavitary infiltrates on imaging
- Prior MRSA infection or colonization
- Recent hospitalization with IV antibiotics
Add: Vancomycin 15 mg/kg IV every 8-12 hours (target trough 15-20 mg/mL) OR linezolid 600mg IV every 12 hours. 2
Duration of Therapy
Treat for a minimum of 5 days and until the patient is afebrile for 48-72 hours with no more than one sign of clinical instability. 2 For uncomplicated CAP, 5-7 days is typically sufficient. 2
Extend duration to 14-21 days for: 2
- Legionella pneumophila
- Staphylococcus aureus
- Gram-negative enteric bacilli
Transition to Oral Therapy
Switch from IV to oral antibiotics when the patient is: 2
- Hemodynamically stable
- Clinically improving
- Able to ingest medications
- Has normal gastrointestinal function
This typically occurs by day 2-3 of hospitalization. 2
Critical Pitfalls to Avoid
Never delay the first antibiotic dose beyond 8 hours in hospitalized patients, as this increases 30-day mortality by 20-30%. 2 Administer the first dose in the emergency department. 2
Avoid macrolide monotherapy in hospitalized patients, as this provides inadequate coverage for typical bacterial pathogens like S. pneumoniae. 2 Always use combination therapy or a respiratory fluoroquinolone.
Do not automatically escalate to broad-spectrum antibiotics based solely on PSI score without documented risk factors for resistant organisms. 2 This increases resistance and adverse effects without improving outcomes.
Obtain blood and sputum cultures before initiating antibiotics in all hospitalized patients to allow pathogen-directed therapy and de-escalation. 2