In this episode, I’ll discuss a web-based program to estimate vancomycin AUC from a single trough value.
Vancomycin guidelines published in March of 2020 have recommended AUC based monitoring over trough-based monitoring due to a reduction in AKI events when AUC based monitoring is used. However, methods to dose vancomycin by AUC are usually more complicated than trough based dosing, especially when more than 1 level is required. This makes the implementation of the new recommendations challenging for some institutions.
A website called Vancopk.com provides numerous open access vancomycin related calculators, one of which uses a single trough value to estimate vancomycin AUC. The method used is an analytic equation derived from trough-only data. This model assumes the vancomycin trough level is at steady-state and assumes a population based Vd that varies according to the patient’s age and weight. The author of the website has recently published a retrospective, observational study in the American Journal of Health System Pharmacy looking at the accuracy of vancomycin AUC values estimated with trough-only data in a veteran population.
The study looked at over 250 patients from 5 Veterans Affairs hospitals across the US. Patients had to have stable renal function and ICU patients were allowed to be included in the data if they were judged to be clinically stable. The VancoPK model was compared with 3 other methods. The VancoPK model was the most accurate and precise of all methods tested, yielding a mean trough-only AUC of 491, with a correlation coefficient of 0.925.
The mean age of the patients in the study was 68, and there were only 2 patients under 40 so results cannot confidently be extrapolated to younger populations based on this data set. However the VancoPK model did perform very well in patients age 80 or greater with a mean trough-only AUC of 484.
95% of the values from VancoPK calculations were within 82 points of the actual AUC, so the author recommends targeting an AUC of 500 to be within the target range of 400-600, although this does assume a MIC value of 1.
The formula behind VancoPK was published previously in the Journal of Clinical Pharmacy and Therapeutics and is explained by the author at https://www.vancopk.com/vanco-kinetics-review/
The ability to get accurate and precise estimates of AUC based off of a single trough value makes implementing AUC-based vancomycin dosing no more complicated than trough-based dosing. The calculator for estimating vancomycin AUC by VancoPK appears to be a practical solution to the last barrier many hospitals face in order to convert to AUC-based dosing of vancomycin.
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