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Top Guns: The "Maverick" and "Goose" of Empiric Therapy.

BACKGROUND
Vancomycin and piperacillin-tazobactam are commonly used first guns in the empiric management of critically ill patients. Current studies suggest an increased prevalence of acute kidney injury with concomitant use, however, these studies are few and limited by small sample size. The purpose of this study was to compare the prevalence of nephrotoxicity after treatment with vancomycin alone and concomitant vancomycin and piperacillin-tazobactam treatment at our institution.


HYPOTHESIS
Concomitant vancomycin and piperacillin-tazobactam-treated patients will experience greater prevalence of nephrotoxicity compared with vancomycin-only treated patients.


METHODS
This was a retrospective cohort of patients treated with vancomycin for gram-positive or mixed infections in our facility from 2005 to 2009 who were not receiving hemodialysis at the time of admission. Included patients were stratified by treatment with vancomycin, vancomycin/piperacillin-tazobactam, or vancomycin/an alternative gram-negative rod (GNR) antibiotic. p values for categorical variables were computed using χ(2) while continuous variables were computed using Kruskal-Wallis. Variables deemed statistically significant (< 0.05) were included in the multivariable, log-binomial regression model. Relative risk (RR) and 95% confidence intervals (CI), and p values were computed using a generalized estimating equation (GEE) approach with robust standard errors (i.e., Huber White "sandwich variance" estimates) to accommodate a correlated data structure corresponding to multiple episodes of infection per individual.


RESULTS
A total of 530 patients with 1,007 episodes of infection, were treated with vancomycin (150 patients/302 episodes of infection), vancomycin/piperacillin-tazobactam (213 patients/372 episodes of infection), or vancomycin/GNR alternative (167 patients/333 episodes of infection). Patient demographics, comorbidities, sites of infection, and organisms of infection were compared among groups. After adjusting for statistically significant variables, neither vancomycin/piperacillin-tazobactam (RR = 1.1, 95% CI = 0.99-1.2; p = 0.073) nor vancomycin/GNR alternative (RR = 1.1, 95% CI = 0.98-1.2; p = 0.097) were found to be associated with an increased risk for nephrotoxicity compared with vancomycin alone.


CONCLUSION
A difference in nephrotoxicity was not observed between vancomycin and vancomycin/piperacillin-tazobactam-treated patients at our institution. Concomitant use as empiric therapy is appropriate, although larger sample sizes are needed to analyze closely this relation among at-risk subsets of this population.