Initial antibiotic selection and patient outcomes: observations from the National Pneumonia Project.

Background: Guidelines for empirical treatment of hospitalized patients with pneumonia provide specific recommendations for antibiotic selection that are primarily based on findings from observational studies.

Methods: We conducted a retrospective study of 27,330 community-dwelling, immunocompetent Medicare patients (age, >65 years) with pneumonia who were hospitalized in 1998-1999 and 2000-2001. Associations between initial antimicrobial regimens and risk-adjusted mortality were assessed, accounting for differences in patient characteristics, comorbidities, illness severity, geographic location, and processes of care. Treatment with nonpseudomonal third-generation cephalosporin monotherapy constituted the reference group for comparisons.

Results: For patients not in the intensive care unit, initial treatment with fluoroquinolone monotherapy was associated with reduced in-hospital mortality, 14-day mortality, and 30-day mortality rates (adjusted odds ratio [AOR] for 30-day mortality, 0.7; 95% confidence interval [CI], 0.6-0.9; P = .001). The combination of a cephalosporin plus a macrolide was associated with reduced 14-day and 30-day mortality rates (AOR for 30-day mortality, 0.7; 95% CI, 0.6-0.9; P < .001). For intensive care unit patients, the combination of a cephalosporin and a macrolide was associated with reduced in-hospital mortality (AOR, 0.6; 95% CI, 0.3-0.9; P = .018).

Conclusions: Initial antimicrobial treatment with the combination of a second- or third-generation cephalosporin and a macrolide or initial treatment with a fluoroquinolone was associated with a reduced 30-day mortality rate, compared with treatment with third-generation cephalosporin monotherapy, among non-intensive care unit patients. Although our results are consistent with other observational studies, controversy continues to exist about the use of nonexperimental cohort studies to demonstrate associations between processes of care, such as antibiotic selection, and patient outcomes.