PHARMACOLOGY
Outpatient Treatment of Community-Acquired Pneumonia in the Emergency Department
SAEM PULSE | MARCH-APRIL 2025
By Kimberly Won, PharmD, on behalf of the SAEM Academic Emergency Medicine Pharmacists Interest Group
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Community-acquired pneumonia (CAP) is a common condition encountered in the emergency department (ED). Many patients can be safely discharged with an outpatient treatment plan. Empiric CAP treatment should cover common bacterial pathogens, including Streptococcus pneumoniae, Haemophilus influenzae, Moraxella Catarrhalis, as well as atypical bacteria such as Chlamydia pneumoniae, Mycoplasma pneumoniae, and Legionella species. For patients with risk factors for methicillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa (P. aeruginosa)—such as a prior infection with these pathogens or recent hospitalization with parenteral antibiotics in the past 90 days—additional coverage should
be considered. The 2019 American Thoracic Society (ATS)/Infectious Diseases Society of America (IDSA) CAP guidelines recommend a short course of antibiotics (e.g., five to seven days), with at least five days as the minimum duration. For CAP caused by MRSA or P. aeruginosa, a seven-day course is reasonable. For healthy patients without comorbidities (e.g., chronic heart, lung, liver, or renal disease; diabetes mellitus; alcoholism; malignancy; asplenia) and without risk factors for MRSA or P. aeruginosa (e.g., prior MRSA or P. aeruginosa infection or recent hospitalization with parenteral antibiotics in the last 90 days), monotherapy with amoxicillin, doxycycline, or a macrolide (e.g., azithromycin, clarithromycin) is appropriate. For
patients with comorbidities, the 2019 ATS/IDSA guidelines recommend broad-spectrum coverage with a combination of a beta-lactam (e.g., amoxicillin/clavulanate or a secondor third-generation cephalosporin) plus a macrolide or doxycycline, or monotherapy with a respiratory fluoroquinolone (e.g., levofloxacin, moxifloxacin). See Table 1.
For monotherapy, should I prescribe doxycycline or azithromycin for CAP?
Historically, azithromycin monotherapy (i.e., Z-Pak) has been commonly used for CAP, but pneumococcal resistance to macrolides (e.g., azithromycin) now exceeds 30% in some regions of the United States, reducing its effectiveness for treating CAP. If an institution’s local antibiogram