What are the first line antibiotics for community-acquired pneumonia?

First-Line Antibiotics for Community-Acquired Pneumonia

For outpatient treatment of community-acquired pneumonia (CAP) in previously healthy adults, amoxicillin 1g three times daily is the recommended first-line antibiotic therapy, with doxycycline or macrolides as alternatives. 1

Outpatient Treatment

Previously Healthy Adults (No Comorbidities)

• First choice: Amoxicillin 1g three times daily 1
• Alternatives:
  • Macrolide (erythromycin, azithromycin, or clarithromycin) 2
  • Doxycycline 100mg twice daily 2, 1

Adults with Comorbidities (COPD, diabetes, heart failure, etc.)

• First choice: Advanced macrolide (azithromycin or clarithromycin) or respiratory fluoroquinolone 2
• If recent antibiotic therapy (within past 3 months):
  • Respiratory fluoroquinolone alone OR
  • Advanced macrolide plus a β-lactam 2, 3

Special Considerations

• Recent antibiotic exposure: Choose a different class than recently used to reduce risk of resistance 2
• Suspected aspiration pneumonia: Amoxicillin-clavulanate or clindamycin 2

Inpatient Treatment (Non-ICU)

• Preferred regimens:
  • Combination therapy: β-lactam (ampicillin-sulbactam, cefotaxime, ceftriaxone, or ceftaroline) plus a macrolide 2
  • Monotherapy: Respiratory fluoroquinolone (levofloxacin 750mg daily or moxifloxacin 400mg daily) 2

Severe CAP (ICU Patients)

• Standard treatment: β-lactam plus either a macrolide or respiratory fluoroquinolone 2
• When Pseudomonas is a concern: Antipseudomonal β-lactam plus either ciprofloxacin or an aminoglycoside plus a macrolide 2

Treatment Duration

• Standard duration: 5-7 days for most cases 1
• Extended treatment (14-21 days) for suspected Legionella, staphylococcal, or gram-negative enteric bacilli pneumonia 2

Important Considerations

• Fluoroquinolone caution: Despite their effectiveness, fluoroquinolones should be reserved for specific situations due to potential adverse effects including tendinopathy, peripheral neuropathy, and CNS effects 2, 1
• Treatment assessment: Evaluate response to treatment at day 2-3 for hospitalized patients or day 5-7 for outpatients 1
• Switching from IV to oral: Hospitalized patients may transition from intravenous to oral antibiotics once clinically improved and able to tolerate oral medications, typically within the first three days 3

Regional Variations in Guidelines

• European guidelines tend to favor aminopenicillins (amoxicillin) as first-line therapy 2
• North American guidelines have historically favored macrolides but are increasingly recommending amoxicillin as first-line therapy 1
• British Thoracic Society recommends amoxicillin as preferred first-line therapy, with erythromycin as an alternative for penicillin-allergic patients 2

The choice of antibiotic should consider local resistance patterns, patient risk factors, and previous antibiotic exposure to maximize effectiveness while minimizing the development of resistance 2, 1.