2025 Southeastern Residency Conference

Title: Pre/Post Analysis of Vancomycin Dosing Guidance in Patients with Obesity in the Hospital Setting


Authors: Courtney Feagin, Kelly Gamble, Hannah Schmoock


Background: Pharmacokinetic data for patients with obesity is not readily available for most medications, and pharmacokinetic profiles vary greatly between patients making dosing difficult to standardize. Supratherapeutic doses of vancomycin can lead to nephrotoxicity and ototoxicity, thus leading to the need for close monitoring of vancomycin levels. Currently, there is limited guidance on vancomycin dosing recommendations in this population. The purpose of this study is to evaluate the effects of a vancomycin dosing in obesity guidance document on dosing efficacy and patient outcomes.  


Methods: This institutional review board approved, retrospective, single-center pre-post cohort study utilized an electronic list of adult patients hospitalized at McLeod Regional Medical Center between March 2024 and February 2025. The pre-group patients were evaluated between March 2024 and September 2024, and the post-group patients were evaluated between November 2024 and February 2025. Patients were included if they had a body mass index (BMI) of ≥ 30 kg/m2 on admission, received at least one dose of intravenous vancomycin, and had at least one vancomycin level drawn at steady state. Patients were excluded if they had baseline severe renal impairment (including acute kidney injury (AKI), hemodialysis, continuous renal replacement therapy, or peritoneal dialysis), pregnant or breastfeeding, reported an allergy to vancomycin, or if vancomycin was initiated at an outside institution. An internal guidance document was created by the infectious disease pharmacy team to aid with dosing vancomycin in patients with obesity, and it was presented to inpatient pharmacists during October 2024. Data was collected via an electronic, password protected spreadsheet accessible only to the primary study investigators. The primary outcome measured was the incidence of therapeutic doses of vancomycin according to target trough levels. Secondary outcomes measured were the incidence of obese patients receiving therapeutic doses of vancomycin according to target area under the curve (AUC) values, incidence of acute kidney injury (AKI), non-therapeutic trough levels at steady state, and non-therapeutic AUC values at steady state.    


Results: Overall, 905 patients were screened for inclusion: 597 patients in the pre-guidance document group and 308 patients in the post-guidance document group. In the pre-group, 550 patients were excluded, and 45 patients were included. In the post-group, 283 patients were excluded, and 23 patients were included.  The overall population is reflective of 61.8% (n=42/68) male, median age of 56 years old (interquartile range [IQR] 46 to 63), median BMI of 35.9 kg/m2 (IQR 32.3 to 41.4), and median Charleson Comorbidity Score of 2 (IQR 1 to 4). The primary outcome was seen in 26.7% (n=12/45) of patients in the pre-group and 34.8% (n=8/23) of patients in the post-group (p=0.49). Secondary outcomes in both groups are as follows: patients with AKI at 72 hours post discontinuation of vancomycin (17.8% vs. 21.7%, p=0.69), patients with a therapeutic AUC (60% vs. 56.5%, p=0.78), subtherapeutic trough level (35.6% vs. 30.4%, p=0.67), supratherapeutic trough level (37.8% vs. 34.8%, p=0.81), subtherapeutic AUC (17.8% vs. 17.4%, p=1.0), and supratherapeutic AUC (17.8% vs. 21.7%, p=0.72).  


Conclusion: This retrospective cohort study did not find that there was a statistically significant difference between patients whose vancomycin was dosed with or without implementation of a pharmacy dosing guidance document. However, this could have been impacted by many different factors that would need to be reevaluated in future studies. These strategies may include requiring use of the dosing guidance document, re-educating pharmacists on timing of troughs and using the guidance document, extending the study timeframe, and conducting the study after the national fluid shortage resolves.