Community-Acquired Pneumonia (CAP) is an acute infection of the pulmonary parenchyma accompanied by symptoms of acute illness and abnormal chest findings.
It is a lower respiratory tract infection acquired in the community within 24 hours to <2 weeks or occurring ≤48 hours of hospital admission in patients who do not meet the criteria for healthcare-associated pneumonia.
It occurs at the highest rates in the very young and the very old.
Potentially life-threatening especially in older adults and those with comorbid disease.

Principles of Therapy

  • Antibiotics should be initiated as soon as possible upon the diagnosis of community-acquired pneumonia (CAP)
  • Consider local antimicrobial resistance patterns when choosing an antibiotic
  • Among patients with recent antibiotic exposure, do not use antibiotics in the same class as the patient had been receiving previously
  • Infection with anaerobes should also be considered as possible causative organisms in patients with risk of aspiration
  • In patients with low severity, consider a 5-day single antibiotic course
    • May extend duration if patient is still symptomatic after 3 days of treatment
    • Dual antibiotic therapy & quinolones should be avoided in low-severity patients
  • In patients with moderate-high severity, a 7-10-day antibiotic course is recommended
    • Dual antibiotic therapy (Amoxicillin plus a macrolide) is recommended for patients with moderate severity CAP
    • Dual antibiotic therapy with a beta-lactamase stable beta-lactam plus a macrolide is recommended for high severity CAP patients
  • In patients with high-risk pneumonia, the parenteral route is recommended for all antimicrobial administration because the severity of the condition may result in a low perfusion state


Recommended Empiric Antibiotic Therapy
Potential Pathogens Patient Condition Antibiotic
Low-risk Pneumonia
Streptococcus pneumoniae
Haemophilus influenzae
Chlamydophilia pneumoniae Mycoplasma pneumoniae
Moraxella catarrhalis
Enteric Gram-negative bacilli (among those with comorbid illnesses)
Previously healthy

Amoxicillin or
Extended macrolides1 (Azithromycin or Clarithromycin)

  • If with high rates of macrolide-resistant S pneumoniae, consider recommendations below for patients with stable comorbid illness
With stable comorbid illness Beta-lactam or beta-lactamase inhibitor combination (BLIC)² or 2nd generation cephalosporins³ with or without extended macrolides1
Co-amoxiclav or Sultamicillin or  Cefuroxime axetil with or without Azithromycin or Clarithromycin
Moderate-risk Pneumonia
S pneumoniae
H influenzae
C pneumoniae
M pneumoniae
M catarrhalis

Enteric Gram-negative bacilli
L pneumophila
Anaerobes (in patients with risk of aspiration)
- Non-antipseudomonal beta-lactam (BLIC, Cephalosporins) intravenous2 (IV) plus
Extended macrolides1 or respiratory fluoroquinolones6

Ampicillin-Sulbactam or
Cefuroxime or Ceftriaxone plus
Azithromycin or Clarithromycin or Levofloxacin or Moxifloxacin

  • If there is a suspicion of aspiration pneumonia and Ampicillin-Sulbactam and/or Moxifloxacin was used, adding of another antibiotic for an additional anaerobic coverage is not needed
  • May add Clindamycin to the regimen if another combination is used to cover for microaerophilic streptococci
High-risk Pneumonia
S pneumoniae
H influenzae
C pneumoniae
M pneumoniae
M catarrhalis

Enteric Gram-negative bacilli
L pneumophila
Anaerobes (among those w/ risk of aspiration)
Staphylococcus aureus
Pseudomonas aeruginosa
No risk for P aeruginosa Non-antipseudomonal beta-lactam IV4  plus
Extended macrolides IV1 or
Respiratory fluoroquinolones IV6
Ceftriaxone or Ertapenem IV plus
Azithromycin IV or Levofloxacin IV or Moxifloxacin IV
W/ risk for P aeruginosa Antipneumococcal antipseudomonal beta-lactam (BLIC, Cephalosporins, or Carbapenem) IV5 plus
Extended macrolides IV¹ plus 
Piperacillin-Tazobactam or Cefepime or Meropenem plus 
Azithromycin plus 
Gentamicin or Amikacin
Antipneumococcal antipseudomonal beta-lactam (BLIC, Cephalosporins, or Carbapenem) IV5 plus
Ciprofloxacin or high dose Levofloxacin IV
 Piperacillin-Tazobactam or Cefepime or Meropenem plus
Levofloxacin or Ciprofloxacin
 Is MRSA pneumonia is suspected, add:  Vancomycin or Linezolid or Clindamycin

¹Extended macrolides: Azithromycin & Clarithromycin
²Oral beta-lactam or beta-lactamase inhibitor combination (BLIC): Amoxicillin-Clavulanic acid, Sultamicillin
³Oral second-generation Cephalosporins: Cefuroxime axetil
4Non-antipseudomonal beta-lactam (BLIC, Cephalosporins or Carbapenem) IV: Ampicillin-Sulbactam, Cefuroxime Na, Ceftriaxone, Ertapenem
5Antipneumococcal, antipseudomonal beta-lactam (BLIC, Cephalosporins or Carbapenem) IV: Piperacillin-Tazobactam, Cefepime, Imipenem-Cilastatin, Meropenem
6Respiratory fluoroquinolones: Levofloxacin, Moxifloxacin


Low-Risk Pneumonia

  • High-dose Amoxicillin or Co-amoxiclav is preferred
    • Targets >93% of S pneumoniae
    • Comorbidities or recent antimicrobial therapy increase the likelihood of infection with drug-resistant S pneumonia and enteric Gram-negative bacteria which may be treated using a combination of a beta-lactam and a macrolide
  • 2nd generation cephalosporins can be used as an alternative antibiotic therapy for patients with stable co-morbid conditions
  • Less active in vitro than high-dose Amoxicillin

Moderate-Risk and High-Risk Pneumonia

  • Parenteral nonpseudomonal beta-lactams with or without a beta-lactamase inhibitor are recommended; some antibiotics from this class may also have anaerobic activity
    • May be given with either an extended macrolide or a respiratory quinolone
  • Recommended beta-lactams include penicillins, 2nd- and 3rd-generation cephalosporins and carbapenems
  • Combining nonpseudomonal beta-lactams with macrolides results in a significant reduction in mortality
  • Oxacillin
    • Consider giving to patients shown or suspected to have lung abscesses, pneumatoceles or pyothorax, in which Staphylococcus sp is a common etiologic organism
    • The best indicator of S aureus infection is the presence of Gram-positive cocci in clusters in a tracheal aspirate or in an adequate sputum sample


Low-Risk Pneumonia

  • Macrolides and azalides may be better for patients with extrapulmonary physical findings, a feature of pneumonia caused by atypical pathogens
  • Alternative for patients who are hypersensitive to Penicillin
  • Erythromycin is less active against H influenzae
  • Azithromycin is preferred for outpatients with comorbidities (eg COPD) because of H influenzae

Moderate-Risk and High-Risk Pneumonia

  • Combining macrolides with nonpseudomonal beta-lactams results in reduced mortality
  • Adding a macrolide to the antibiotic regimen benefits patients in areas with a high prevalence of Legionella sp

Quinolones with Anti-Pneumococcal Action (Respiratory Quinolones)

Low-Risk Pneumonia

  • Recommended for those with comorbid illnesses or recent antibiotic treatment which increase the chance of infection with resistant S pneumoniae or enteric Gram-negative bacilli

Moderate-Risk Pneumonia

  • May be used alone as an alternative regimen to nonpseudomonal beta-lactam with or without beta-lactamase inhibitor plus a macrolide
  • In areas with high prevalence of pulmonary tuberculosis (TB), they are better reserved as potential 2nd-line agents for the treatment of multidrug-resistant TB
    • Quinolones may mask the clinical features of pulmonary TB and delay its diagnosis

Clindamycin, Metronidazole

Moderate-Risk Pneumonia

  • Add Clindamycin or Metronidazole to the antibiotic regimen in patients with suspected aspiration

Duration of Treatment Based on Etiology

Low-Risk Pneumonia

  • Minimum of 5 days; usual duration is 5-7 days for most pneumonias of bacterial etiology
  • A 3-day course of oral therapy may be possible with azalides

Moderate-Risk And High-Risk Pneumonia

Etiologic Agent Duration of Therapy
  • Most bacterial pneumonias except enteric Gram-negative pathogens (MRSA and MSSA), and P aeruginosa
5-7 days; 3-5 days (azalides) for S pneumoniae
  • Enteric Gram-positive pathogens, S aureus (MRSA and MSSA) & P aeruginosa


  • Non-bacteremic - 7-14 days
  • Bacteremic - longer; up to 21 days


  • Non-bacteremic -  7-21 days
  • Bacteremic - longer; up to 28 days

P aeruginosa

  • Non-bacteremic - 14-21 days
  • Bacteremic - longer; up to 28 days
  • Mycoplasma sp and Chlamydophilia sp
10-14 days
  • Legionella sp
14-21 days; 10 days (azalides)
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