Characteristics and calculations of paired vancomycin measurements for determination of 24-h area-under-curve (AUC)

BACKGROUND: Current pharmacy practice guidelines recommend 24-h area-under-curve (AUC(24)) targets for use of vancomycin against methicillin-resistant Staphylococcus aureus (MRSA). AUC protocol-specific vancomycin orders were begun recently (2022) at our institution. We reviewed initial AUC protocol-associated data and calculations. METHODS: AUC(24) calculations are derived from timed, paired measurements of vancomycin (V1,V2). We retrieved paired (V1,V2) measurements for a 90-day interval. Calculations to obtain AUC(24) were performed according to two accepted methods (A, B) that assume first-order kinetics for vancomycin elimination between V1 and V2. RESULTS: 44 (V1,V2) measurement pairs were from among 27 patients. Dosing intervals were 8, 12, or 24 h. The first-order rate constant k was normally distributed (k = 0.096 ± 0.046 1/h); t(1/2) ranged from 3 to 30 h. For target AUC(24) = 400–600 h × μg/mL, 55% of calculated AUC(24) results were within target. Imprecision for calculated k was predicted to be least when V2 is a trough level. Method B results were greater than Method A results by a factor of 1.07. CONCLUSIONS: 45% of AUC(24) results indicated need for change in dosage. Recommendations are that average results from A and B methods of calculation should be used, and that V1 and V2 should be as widely separated as possible.