Community-acquired pneumonia (CAP) is defined as pneumonia acquired outside of hospitals, (less than 48 hours from hospital admission). Patients will typically present with symptoms including fever, chills, chest pain, cough, sputum production, and dyspnea. Objective findings may include increased HR, respiratory rate >20 breaths/min, elevated WBC, crackles on auscultation, and evidence of consolidation (decreased breath sounds, dullness to percussion). Elderly patients may oftentimes present without many of these signs and symptoms, however.
The severity of CAP is determined by the Pneumonia Severity Index (PSI), defined by the presence of one major criterion or at least three minor criteria. Major criteria include septic shock with the need for vasopressors and respiratory failure requiring mechanical ventilation. The minor criteria include: respiratory rate >30 breaths/min, PaO2/FiO2 ratio <250, multilobar infiltrates, confusion/disorientation, uremia (BUN >20 mg/dL), leukopenia (WBC <4000 cells/mcL), thrombocytopenia (platelet count <100,000/mcL), hypothermia, and hypotension requiring aggressive fluid resuscitation.
Due to the increasing pneumococcal conjugate vaccination rates, the microbial etiology of CAP has been changing, with an increase in viral pneumonia. The bacterial pathogens traditionally implicated in CAP include S. pneumoniae, H. influenzae, M. catarrhalis, S. aureus, and atypicals (M. pneumoniae, Legionella species, C. pneumoniae). The IDSA still recommends empiric antibiotic therapy for CAP due to the proven efficacy and safety of antibiotic regimens and the high mortality of bacterial CAP. Patients treated for outpatient CAP are not recommended to get a pretreatment gram stain or culture. Patients with severe CAP (especially those who are intubated) who are being empirically treated for MRSA or P. aeruginosa, or were hospitalized and received parenteral antibiotics in the past 90 days should receive pretreatment gram staining and culture of respiratory secretions.
Patients on antibiotic therapy for CAP should be treated until clinical stability, and for no less than 5 days (exception possibly being higher dose azithromycin for 3 days). In general, most patients will achieve clinical stability in 2-3 days. Some signs of clinical stability include heart rate <100 bpm, respiratory rate <24 breaths/min, ability to maintain oral intake, and normal mental status.
How does the COVID-19 pandemic impact the 2019 guideline recommendations? The co-chairs from these guidelines offered their own recommendations for this topic. For patients with confirmed COVID-19-related pneumonia, empirical antibiotic coverage is not required, but it is still recommended in all CAP patients without confirmed COVID-19. They did not suggest any changes in the empirical antibiotic regimens, as the relevant pathogens are likely the same in patients with pneumonia with or without COVID-19. They also state that procalcitonin levels could be helpful in limiting antibiotic overuse in patients who have COVID-19-related pneumonia, as a low procalcitonin level may indicate a higher likelihood of viral etiology and thus antibiotics could be withheld or stopped earlier.
Outpatient Community-Acquired Pneumonia (CAP)
Outpatient treatment recommendations are escalated based on the presence of risk factors for MRSA or P. aeruginosa infections or with comorbidities including heart, lung, liver, or renal disease, diabetes mellitus, alcoholism, malignancy, and asplenia.
The recommended empiric regimens for outpatients with no comorbidities are either amoxicillin, doxycycline, or a macrolide (if local pneumococcal resistance <25%). For those patients who do present with comorbidities or risk factors, the recommended empirical therapy includes combination therapy with amoxicillin/clavulanate or a cephalosporin (cefpodoxime, cefuroxime) plus a macrolide or doxycycline. Monotherapy with a respiratory fluoroquinolone (levofloxacin or moxifloxacin) is also an acceptable option.
Nonsevere Inpatient CAP
Nonsevere inpatient CAP should be treated with combination therapy with a beta-lactam (ampicillin-sulbactam, ceftriaxone, cefotaxime, ceftaroline) plus a macrolide (azithromycin or clarithromycin) or monotherapy with a respiratory fluoroquinolone. Add MRSA or P. aeruginosa coverage and obtain cultures/nasal PCR if there is prior respiratory isolation of either.
Severe Inpatient CAP
Empirical therapy recommendations for severe inpatient CAP is combination therapy with a beta-lactam (ampicillin-sulbactam, ceftriaxone, cefotaxime, ceftaroline) plus either a macrolide (azithromycin or clarithromycin) or a respiratory fluoroquinolone. Add MRSA or P. aeruginosa coverage and obtain cultures/nasal PCR if there is prior respiratory isolation of either.
There is a table included below with the empirical treatment options for CAP as well as a separate table for the recommended antibiotic dosing.
|Recommended Empiric Therapy and Dosing|
|Outpatient CAP||Monotherapy:Amoxicillin +/-Doxycycline +/-Macrolide (if local pneumococcal resistance is <25%)|
|Outpatient CAP with comorbidities or risk for MRSA/P. aeruginosa||Combination Therapy: Amoxicillin/clavulanate or cephalosporin and macrolide or doxycycline|
Monotherapy: Respiratory fluoroquinolone
|Non-severe Inpatient CAP||Combination Therapy: Beta-lactam AND Macrolide Monotherapy: Respiratory fluoroquinolone|
Prior respiratory isolation of MRSA or P. aeruginosa: Add coverage and obtain cultures/nasal PCR
Recent hospitalization and IV antibiotics + local risk factors for MRSA or P. aeruginosa: Obtain cultures and only add coverage for positive culture results
|Severe Inpatient CAP||Combination Therapy: Beta-lactam AND Macrolide or a respiratory fluoroquinolone|
Prior respiratory isolation of MRSA or P. aeruginosa or recent hospitalization and IV antibiotics + local risk factors for MRSA or P. aeruginosa: Add coverage and obtain cultures/nasal PCR
|Antibiotic Class||Outpatient Agents and Dosing||Inpatient Agents and Dosing|
|Beta-Lactams/Doxycycline||Amoxicillin 1 g daily|
Amoxicillin/clavulanate 500 mg/125 mg three times daily
Amoxicillin/clavulanate 875 mg/125 mg twice daily
Amoxicillin/clavulanate 2,000 mg/125 mg twice daily
Cefpodoxime 200 mg twice daily
Cefuroxime 500 mg twice daily
Doxycycline 100 mg twice daily
|Ampicillin-sulbactam 1.5-3 g every 6 hours|
Cefotaxime 1-2 g every 8 hours
Ceftriaxone 1-2 g daily
Ceftaroline 600 mg every 12 hours
|Macrolides||Azithromycin 500 mg on day 1, then 250 mg daily|
Clarithromycin 500 mg twice daily
Clarithromycin ER 1,000 mg daily
|Azithromycin 500 mg daily|
Clarithromycin 500 mg twice daily
|Fluoroquinolones||Levofloxacin 750 mg daily|
Moxifloxacin 400 mg daily
|Levofloxacin 750 mg daily|
Moxifloxacin 400 mg daily
|MRSA Coverage||N/A||Vancomycin 15 mg/kg every 12 hours (adjust based on TDM)|
Linezolid 600 mg every 12 hours
|P. aeruginosa Coverage||N/A||Piperacillin-tazobactam 4.5 g every 6 hours|
Cefepime 2 g every 8 hours
Ceftazidime 2 g every 8 hours
Imipenem 500 mg every 6 hours
Meropenem 1 g every 8 hours
Aztreonam 2 g every 8 hours
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Article written by Lincoln Haiby, PharmD Candidate in collaboration with Eric Christianson, PharmD, BCGP, BCPS
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Metlay, JP, et al. Diagnosis and Treatment of Adults with Community-acquired Pneumonia. An Official Clinical Practice Guideline of the American Thoracic Society and Infectious Diseases Society of America. American journal of respiratory and critical care medicine. 2019;200(7):e45-e67. Accessed July 21, 2021.
Metlay JP, Waterer GW. Treatment of Community-Acquired Pneumonia During the Coronavirus Disease 2019 (COVID-19) Pandemic. Ann Intern Med. 2020 Aug 18;173(4):304-305. Epub 2020 May 7. Accessed July 21, 2021.