Introduction: Dosing weight-based medications in patients with obesity is challenging due to the relative composition of muscle, adipose tissue, and plasma proteins differing from that of non-obese patients. As a hydrophilic antibiotic, vancomycin distributes differently in muscle, adipose tissue, and serum. Using doses based on total body weight (TBW) can lead to accumulation and acute kidney injury (AKI) in patients with obesity. The goal of this study is to evaluate the incidence of AKI when using TBW versus adjusted body weight (ABW) in vancomycin dose calculations for patients with a body mass index (BMI) above 30 kg/m2. Methods: A retrospective analysis of supratherapeutic vancomycin trough levels above 20 mcg/mL at the University of Wisconsin Hospitals and Clinics University Hospital and East Madison Hospital between January 1st, 2024 and May 14th, 2025 was conducted. Patients that received renal replacement therapy, with levels drawn > 90 minutes from the expected trough, or with an AKI upon vancomycin initiation were excluded. Incidences were further sorted into patients with BMI ≥ or ≤ 30 kg/m2 and whether these patients developed an AKI within 3 days of the supratherapeutic level. Administered doses were compared to internal guidance to determine which weight was utilized to calculate the final dose. Results: Of the 206 patients identified, 76 met inclusion criteria. Patients ranged from 26 to 80 years old with a median age of 63 years old. Patients were mostly white with 37 males and 39 females included. The distribution of TBW ranged from 42 to 170.6 kilograms, with an average of 85.76 kilograms and a median weight of 82.7 kilograms. BMI also varied across the population set from 16.21 to 62.51. The mean BMI was 30.35 kg/m2 and median was 29.11 kg/m2. Thirty-three patients developed an AKI within 3 days of the supratherapeutic vancomycin trough level. Patients with a BMI > 30 kg/m2 that developed an AKI were more likely to receive a dose based on TBW that resulted in a higher than recommended vancomycin dose (75% compared to 44.4% of those with no AKI and BMI > 30 kg/m2, 40% of those with no AKI and BMI less < 30 kg/m2, and 33.3% of those with AKI and BMI < 30 kg/m2). Conclusions: Using TBW to dose vancomycin in patients with BMI greater than 30 kg/m2 led to higher rates of AKI.
Jasinska et al. (Sun,) studied this question.