Treatment of community-acquired pneumonia typically involves either a respiratory fluoroquinolone or a combination of cephalosporin and a macrolide. Initial broad-spectrum antibiotic therapy should be targeted to patients selected according to risk factors or existing disease. The latest review in our Clinical Practice series is on this topic.
Pneumonia is sometimes referred to as the forgotten killer. The World Health Organization estimates that lower respiratory tract infection is the most common infectious cause of death in the world (third overall), with almost 3.5 million deaths yearly.
• What antibiotic coverage is most appropriate for outpatients with CAP?
For outpatients, coverage of atypical bacterial pathogens is most important, especially for younger adults where herd immunity from extensive pediatric conjugate pneumococcal vaccination has decreased rates of pneumococcal pneumonia. The primary factors discriminating among the large number of approved oral antibiotics are recent antibiotic use (with risk of class resistance) and cost. Macrolides, doxycycline, and fluoroquinolones are the most appropriate agents for the atypical bacterial pathogens.
• What are the current guidelines for antibiotic administration for CAP in a patient admitted to a regular hospital bed versus a bed in the ICU?
For patients admitted to a regular hospital bed, Infectious Diseases Society of America and American Thoracic Society (IDSA-ATS) guidelines recommend first-line treatment with either a respiratory fluoroquinolone (moxifloxacin 400 mg/day or levofloxacin 750 mg/day) or the combination of a second- or third-generation cephalosporin and a macrolide. These recommendations are primarily based on large inpatient administrative databases that demonstrate lower mortality with recommended antibiotic treatment compared to other antibiotics or combinations. Although Streptococcus pneumoniae remains the most common cause of severe CAP requiring ICU admission, combination therapy consisting of a cephalosporin with either a fluoroquinolone or a macrolide is recommended. Observational evidence suggests that the macrolide combination may be associated with better outcomes. Since fluoroquinolones have essentially the same antibacterial spectrum, a benefit of macrolides may be explained by nonbacteriocidal effects such as immunomodulation.
Morning Report Questions
Q: What are the IDSA-ATS guidelines for consideration of ICU admission for patients without an obvious need for such placement?
A: The IDSA-ATS guidelines suggest that the presence of three or more of nine minor criteria warrant consideration of ICU admission. They are confusion, uremia (blood urea nitrogen greater than or equal to 20 mg/dl), tachypnea (greater than or equal to 30 breaths/min), multi lobar radiographic infiltrates, hypoxemia (PaO2/FiO2 <250), thrombocytopenia (<100,000 platelets/mm3), hypotension requiring aggressive fluid resuscitation, hypothermia (core <36 degreesC), and leukopenia (<4000/mm3).
Q: What are the pneumonia-specific risk factors that predict which patients with CAP will have resistant pathogens?
A: The optimal criteria to identify patients appropriate for initial empirical broad-spectrum coverage is unclear. A recent prospective, multicenter study identified six risk factors for pneumonia caused by pathogens resistant to the usual inpatient antibiotic regimens recommended by IDSA-ATS guidelines. They are hospitalization for greater than or equal to 2 days in the previous 90 days, antibiotics in the previous 90 days, nonambulatory status, tube feedings, immunocompromise, and use of gastric acid suppressive agents. These pneumonia-specific risk factors are consistent with other reports indicating that recent antibiotic use or hospitalization and poor functional status are more important predictors of resistant pathogens than nursing home residence alone. Available data suggest that the incidence of multidrug-resistant pathogens generally is not significantly increased unless three or more risk factors are present. However, MRSA [methicillin-resistant Staphylococcus aureus] is an exception: the presence of one MRSA-specific risk factor (prior MRSA infection or colonization, chronic hemodialysis, or heart failure) and another pneumonia-specific risk factor may warrant MRSA coverage (but not dual antipseudomonal antibiotics).