How to classify and treat community-acquired pneumonia (CAP)?

Classification and Treatment of Community-Acquired Pneumonia (CAP)

Community-acquired pneumonia should be classified by severity and treated with appropriate antibiotics based on patient risk factors, with outpatients receiving either monotherapy or combination therapy depending on comorbidities, and inpatients receiving more intensive regimens based on severity and risk for resistant pathogens. 1

Classification of CAP

• CAP severity should be assessed using validated tools to guide site-of-care decisions and treatment intensity 1:

  • For outpatient vs. inpatient decisions: Pneumonia Severity Index (PSI) is recommended as the primary tool, with CURB-65 as an alternative 1
  • For ICU admission decisions: 2007 IDSA/ATS severe CAP criteria are recommended to identify patients requiring intensive care 1

• Patients with severe CAP (requiring ICU) have higher mortality and need more aggressive management and diagnostic testing 1

Treatment of CAP by Patient Category

1. Outpatient Treatment

For healthy adults without comorbidities:

• First-line options (in order of preference):
  • Amoxicillin 1 g three times daily (strong recommendation) 1
  • Doxycycline 100 mg twice daily (conditional recommendation) 1
  • Macrolide (azithromycin 500 mg on day 1, then 250 mg daily OR clarithromycin 500 mg twice daily) - only in areas with pneumococcal resistance to macrolides <25% 1

For adults with comorbidities (chronic heart/lung/liver/renal disease, diabetes, alcoholism, malignancy, asplenia):

• Combination therapy options:
  • Amoxicillin/clavulanate (500/125 mg three times daily, 875/125 mg twice daily, or 2000/125 mg twice daily) OR cephalosporin (cefpodoxime 200 mg twice daily or cefuroxime 500 mg twice daily)
  • PLUS a macrolide or doxycycline 1
• Monotherapy option:
  • Respiratory fluoroquinolone (levofloxacin 750 mg daily, moxifloxacin 400 mg daily, or gemifloxacin 320 mg daily) 1, 2

2. Inpatient Treatment (Non-ICU)

• Standard regimen 1:
  • β-Lactam (ampicillin/sulbactam, cefotaxime, ceftriaxone, or ceftaroline) PLUS macrolide (azithromycin or clarithromycin)
  • OR β-Lactam PLUS respiratory fluoroquinolone

3. Severe CAP (ICU) Treatment

• Standard regimen 1:
  • β-Lactam PLUS macrolide OR β-lactam PLUS fluoroquinolone
  • Add coverage for MRSA if risk factors present
  • Add coverage for Pseudomonas aeruginosa if risk factors present

Special Considerations

Duration of Therapy

• Minimum treatment duration of 5 days for all patients with CAP 1, 3
• Patient should be afebrile for 48-72 hours and have no more than one CAP-associated sign of clinical instability before discontinuing therapy 1, 3
• Longer duration may be needed if initial therapy was not active against the identified pathogen or if complicated by extrapulmonary infection 1, 3

Short-Course High-Dose Therapy

• High-dose levofloxacin (750 mg daily for 5 days) is as effective as conventional 10-day regimens for CAP 2, 4
• Short-course therapy improves compliance and reduces antibiotic exposure 5

Diagnostic Testing

• Empiric antibiotic therapy should be initiated in adults with clinically suspected and radiographically confirmed CAP regardless of initial serum procalcitonin level 1
• Urine antigen testing for pneumococcal and Legionella antigens is not routinely recommended except in severe CAP or when epidemiologically indicated 1

Treatment Algorithm

1. Assess severity using PSI or CURB-65 to determine treatment setting (outpatient vs. inpatient)
2. Evaluate risk factors for drug-resistant pathogens (recent hospitalization, prior antibiotics, healthcare exposure)
3. Select empiric therapy based on:
   • Treatment setting (outpatient, inpatient, ICU)
   • Presence of comorbidities
   • Risk for resistant pathogens
4. Reassess after 48-72 hours for clinical response
5. De-escalate therapy if a pathogen is identified
6. Complete appropriate duration (minimum 5 days) and ensure clinical stability before discontinuation

Common Pitfalls to Avoid

• Failing to assess severity appropriately, leading to inappropriate site-of-care decisions 1
• Using macrolide monotherapy in areas with high pneumococcal resistance 1
• Continuing antibiotics beyond necessary duration without clinical indication 3
• Not considering pathogen-specific treatment when a causative organism is identified 1
• Overlooking the need for coverage against resistant pathogens in patients with risk factors 1