Body Mass Index of Elderly Patients with Normal Renal Function as a Determining Factor for Initial Vancomycin Regimen Designing.

Introduction: Currently, the use of actual body weight is recommended for dosing in vancomycin regimen designs, and it is important to perform therapeutic drug monitoring for efficacy and safety. However, the method to determine the appropriate vancomycin regimen for underweight or obese patients remains controversial. The aim of this study was to evaluate the impact of body mass index (BMI) on the relationship among vancomycin doses, trough concentration, and area under the curve (AUC). In addition, we identified the group of patients who were potentially more affected by BMI and evaluated the optimal dosing regimen to achieve the target AUC.

Methods: We retrospectively collected data from 462 patients who received vancomycin at the Osaka City University Hospital between January 2013 and September 2019. Patients were classified by their BMI group (underweight <18.5, normal weight 18.5-24.9, and obese ≥25.0 kg/m2). We assessed the association between vancomycin dose versus trough concentration or AUC as well as dose-adjusted trough concentration and AUC in each BMI subgroup to determine the doses for achieving the target AUC.

Results: The dose-adjusted trough concentration and AUC in elderly patients with normal renal function appeared to increase significantly with an increase in BMI (p < 0.05). Vancomycin doses that enabled the achievement of AUC400 in elderly patients with normal renal function decreased with increasing BMI: 17.7, 15.8, and 12.9 mg/kg per time in the underweight, normal weight, and obesity groups, respectively (p < 0.05).

Conclusion: Elderly patients with normal renal function were the most affected by BMI on vancomycin trough concentration and AUC. The vancomycin regimen design in these patients should be adjusted carefully, not only based on the patient's renal function but also based on BMI.