Methods of Therapeutic Drug Monitoring to Guide Vancomycin Dosing Regimens: Trough Concentration versus Ratio of Area Under the Curve to Minimum Inhibitory Concentration

Abstract

Background: The most recent vancomycin monitoring guideline recommends targeting a value for area under the curve (AUC) of 400 to 600 mg*h/L, with an assumed minimum inhibitory concentration (MIC) of 1 mg/L. Few studies have investigated the effect of this method on vancomycin dosing regimens, relative to a target trough concentration of 15 to 20 mg/L. Objective: To compare vancomycin dosing regimens generated with the 2 monitoring methods. Methods: This retrospective chart review included hospitalized patients who received vancomycin between May 2019 and April 2020. The dosing regimens were compared, with the paired Student t test, in terms of unit dose, daily dose, and dosing interval. Variables of interest were collected from electronic medical charts. A pharmacy resident used first-order pharmacokinetic equations to determine dosing regimens based on AUC monitoring. Local pharmacists retrospectively determined dosing regimens for trough-based monitoring. Results: Of 100 courses of treatment initially identified, 66 were included in the analysis. The unit dose was similar with the 2 methods (1086 mg with AUC-based monitoring versus 1100 mg with trough-based monitoring; p = 0.62). AUC monitoring was associated with a 12.8% lower daily dose (2294 mg versus 2630 mg; p < 0.001) and a 13.5% longer dosing interval (13.24 h versus 11.67 h; p < 0.001) relative to trough-based monitoring. AUC monitoring also generated a lower extrapolated trough concentration (12.90 mg/L versus 16.22 mg/L; p < 0.001). Conclusions: A target trough concentration of 15 to 20 mg/L was confirmed as being unnecessarily high. AUC monitoring could allow a reduction in daily vancomycin dose and an extension of the dosing interval relative to trough-based monitoring.