085: Vancomycin Associated Nephrotoxicity & Clinical Outcomes Assessment in Geriatric Empiric Dosing Strategies (VANCO-AGED)

Statement of Purpose: The Infectious Disease Society of America (IDSA) guidelines have shifted towards AUC/MIC monitoring to reduce the risk of vancomycin nephrotoxicity. However, trough-based monitoring remains more feasible at our site due to the substantial cost and time constraints of Bayesian modelling. Age-related physiological changes put geriatrics at a higher risk of experiencing vancomycin accumulation and subsequent nephrotoxicity. Elderly patients have decreased muscle mass, which results in lower measured serum creatinine, and a higher volume of distribution. These factors lead to a longer half-life and slower clearance when it comes to vancomycin. Despite the altered pharmacokinetics, there is limited evidence available to guide empiric vancomycin dosing strategies in geriatrics. The objective of this study is to evaluate the safety and efficacy of empiric vancomycin dosing frequencies in elderly patients.

Description of Methods & Materials: This study was a single centre, retrospective health record review. Patients included were aged 80 years and older, hospitalized between September 2020 and March 2022, and received intravenous vancomycin therapy for a minimum of 72 hours with at least one trough level recorded at steady state. Patients receiving dialysis or a continuous vancomycin infusion were excluded. The primary objectives were to characterize empiric vancomycin dosing regimens and to determine the proportion of patients achieving subtherapeutic ( < 10 mg/L), therapeutic (10-20 mg/L) and supratherapeutic ( >20 mg/L) trough levels. Secondary objectives were to determine the time to therapeutic range, incidence of acute kidney injury (AKI) as defined by the Kidney Disease Improving Global Outcomes (KDIGO) criteria, incidence of retreatment during admission and the incidence of readmission within 30 days.

Data & Results: This study included 70 patients with mean age 86 ± 4 years, weight 73 ± 21 kg and serum creatinine 108 ± 60 µmol/L. The mean maintenance dose was 19 ± 7 mg/kg/day, with 86% of the study population receiving a mean loading dose of 24 ± 4 mg/kg. Dosing frequencies captured in this study were Q12H (31%), Q24H (66%), Q36H (1%) and Q48H (1%). Therapeutic range was achieved by 8 (36%) patients on Q12H dosing, 28 (61%) patients on Q24H dosing and 1 (100%) patient on Q36H dosing. Mean time to therapeutic range was 79 ± 61 hours. Supratherapeutic levels were seen for 13 (59%) patients on Q12H dosing, 10 (22%) patients on Q24H dosing and 1 (100%) patient on Q48H dosing. Nineteen (27%) patients experienced an AKI. Two (3%) patients experienced a Stage 3 AKI as per KDIGO criteria, which had a higher occurrence on Q12H dosing (5%) compared to Q24H dosing (2%). Five (7%) patients required retreatment during admission and 1 (1%) required readmission within 30 days for the same infection.

Interpretation, Conclusion or Significance: In this geriatric cohort, the most commonly observed vancomycin dosing frequency was Q24H. There was a signal towards supratherapeutic levels and worse nephrotoxic outcomes seen in patients on Q12H dosing. Limited patients were on Q36H and Q48H dosing, which prevented interpretation of these results. Larger prospective studies are warranted to guide empiric vancomycin dosing strategies in geriatric patients.

Disclosures: