Vancomycin-associated nephrotoxicity: The obesity factor

Background: Current recommendations suggest that vancomycin dosing utilize actual rather than ideal body weight in obese patients. Thus, obese patients may be at greater risk for nephrotoxicity. The purpose of this study was to compare the incidence of nephrotoxicity in vancomycin-treated obese and lean patients at our institution, where unadjusted, actual body weight-based dosing (capped at 2 g per dose twice daily) is used. We expected obese patients to experience a greater incidence of nephrotoxicity than lean patients. Methods: This study examined a retrospective cohort of patients treated with vancomycin for gram-positive or mixed infections in our facility from 2005-2009 who were not receiving hemodialysis at the time of admission. Patients were stratified by body mass index (BMI; obese ≥30 kg/m² vs. lean <30 kg/m²). Relative risk (RR), 95% confidence intervals (CIs), and p values were computed using a generalized estimating equation to accommodate a correlated data structure corresponding to multiple episodes of infection per individual. Multivariable analysis was performed. Results: A total of 530 patients (207 obese; 323 lean) with 1,007 episodes of infection were treated with vancomycin. Patient demographics, co-morbidities, sites of infection, and infecting organisms were similar in the two groups. Female gender (p=0.042), diabetes mellitus (DM) (p=0.018), and hypertension (HTN) (p=0.0009) were more often associated with obesity, whereas allografts (p=0.022) and peripheral vascular disease (p=0.036) were more often present in lean patients. The Acute Physiology and Chronic Health Evaluation II score >21 was the only variable associated with nephrotoxicity (p=0.039). After adjusting for statistically significant variables, obesity was found not to be associated with a greater risk of nephrotoxicity (RR=0.98; 95% CI=0.93-1.04; p=0.59). Conclusion: No difference in nephrotoxicity was observed between lean and obese patients treated with vancomycin at our institution.