O19 – Vancomycin-Associated Nephrotoxicity; the Obesity Factor
Author(s):
Background: Current recommendations suggest vancomycin dosing utilize actual versus ideal body weight in obese patients due to accelerated renal clearance in this population. Additionally, an increase in multidrug resistant bacteria due to poor penetrance in certain tissues (e.g., lung) has resulted in higher vancomycin therapeutic ranges. Thus, obese patients may be at increased risk for nephrotoxicity. The purpose of this study was to compare the incidence of nephrotoxicity between vancomycin-treated, obese and lean patients at our institution where unadjusted, actual body weight-based dosing is used.
Hypothesis: Obese patients will experience greater incidence of nephrotoxicity compared to lean patients.
Methods: Patients treated with vancomycin for Gram positive or mixed infections in our facility from 1996-2008 were identified. Non-dialysis dependent patients were categorized by body mass index (BMI, lean<30, obese≥30). Categorical and continuous data were analyzed. Univariate, logistic regression was performed to evaluate each variable’s association with nephrotoxicity (i.e., 50% or 0.5mg/dL increase in baseline creatinine).
Results: 117 patients (lean=72 vs. obese=45) with 211 separately identified infections (136vs75) met our inclusion criteria. Patient demographics, comorbidities (including initial creatinine levels), sites of infection, and organisms of infection were similar between groups. APACHE II scores (p=0.0059) and Escherichia coli prevalence (p=0.0002) were greater, while prevalence of nosocomial infection (p=0.014) was less among obese compared to lean patients; however these differences were not associated with nephrotoxicity by logistic regression. Obese patients received vancomycin at similar trough levels (17±11vs14±8.3mg/L;p=0.10) for similar duration (9.8±9.9vs8.5±6.5days;p=0.92), and experienced similar maximum creatinine levels (1.6±1.3vs1.8±1.3;p=0.092), incidences of nephrotoxicity [13(18%)vs10(22%);p=0.58], and mortality [10(14%)vs8(18%);p=0.57].
Conclusions: A difference in nephrotoxicity was not observed between lean and obese patients treated with vancomycin at our institution while using actual weight-based dosing. Additionally, similar trough levels (within the recommended target guidelines) were obtained. Unadjusted, actual weight-based dosing for vancomycin treatment among obese patients is appropriate, though larger sample sizes are needed to closely analyze this relationship among “at-risk” subsets of this population.