393Vancomycin Dosing in Obese Patients

Background. Current guidelines for systemic vancomycin dosing recommended using actual body weight (ABW) regardless of body mass index (BMI). We sought to evaluate the effect of this dosing strategy in obese patients with BMI ≥35. Methods. Retrospective cohort study of patients ≥18 years old with a BMI ≥35 hospitalized between January 1, 2011 and December 31, 2013 with at least 3 doses of intravenous vancomycin. Inclusion required a normal baseline creatinine clearance (CrCl ≥45 mL/minute) and at least 1 appropriate vancomycin trough measured before the 4or later dose. Patients were excluded if they received a loading dose or if the maintenance dose was changed before the first trough was measured. We collected data on patient’s age, gender, weight (actual, ideal, and dosing), baseline creatinine, calculated CrCl, administered vancomycin dose (including frequency and total daily dose), and vancomycin trough. Linear regression was used to predict the vancomycin trough based on each of these clinical predictors. Results. The 68 patients identified had a significant positive linear relationship between vancomycin total daily dose (TDD) (mg/kg/day) based on ideal body weight (IBW) and vancomycin trough (p 0.001). The relationship was not significant for vancomycin TDD based on ABW (p 0.072). Other predictors of vancomycin trough included age, gender, and baseline serum creatinine. Multivariable modeling including these predictors, along with vancomycin TDD based on IBW, showed moderate correlation between predicted and actual vancomycin troughs (R>0.41). For the average patient in our study, initial doses of 30 mg/kg/day (IBW) predicted vancomycin troughs of 10-15 mcg/mL. To achieve targets of 15-20 mcg/mL, our model suggested that initial doses of 45-60 mg/kg/day (IBW) should be used. Younger patients and male patients were less likely to achieve therapeutic targets without this higher dosing. Conclusion. For patients with a BMI ≥35, vancomycin dosing based on IBW rather than ABWappears to be more predictive of vancomycin trough, with initial doses of at least 45 mg/kg/day (IBW) more likely to achieve higher vancomycin trough targets. Given the only moderate correlation, it remains important to follow vancomycin troughs and adjust dosing accordingly. Disclosures. All authors: No reported disclosures.