Evaluation of Vancomycin Accumulation in Patients With Obesity.

Background: Current vancomycin guidelines recommend early and frequent area-under-the-curve monitoring in patients with obesity. Vancomycin's volume of distribution is likely altered in patients with obesity, which may result in lower serum concentrations initially but lead to accumulation with continued use. The objective of this study was to evaluate the incidence of vancomycin accumulation in patients with obesity and identify potential factors associated with accumulation. Methods: This was a single-center, retrospective, observational study at a tertiary academic medical center. Adult patients with a body mass index (BMI) ≥ 30 kg/m2 and ≥ 2 vancomycin serum trough concentrations drawn in 2019 were screened for inclusion. The major endpoint was the incidence of vancomycin accumulation defined as ≥ 20% increase in trough concentration within the first 10 days of therapy. Key minor endpoints included incidence of acute kidney injury (AKI) and factors associated with accumulation. Results: Of the 443 patients screened, 162 were included. The median age was 56.5 years (interquartile range [IQR], 43-65.3), and 62.3% were male. The median weight was 112.7 kg (IQR, 99.8-122.6) and the median BMI was 36.8 kg/m2 (IQR, 33.1-41). The total daily dose median at initiation was 28.7 mg/kg per day (IQR, 25.4-31.2). Accumulation occurred in 99 of 162 patients (61.1%) and AKI occurred in 20 of 140 patients (14.3%). No specific factors were found to be associated with accumulation. Conclusions: Patients with obesity are likely to experience vancomycin accumulation within the first 10 days of therapy. Clinicians should use frequent monitoring of vancomycin and use caution when interpreting early concentrations in patients with obesity.