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 (AUC24) 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: AUC24 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 AUC24 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); t1/2 ranged from 3 to 30 h. For target AUC24 = 400–600 h × μg/mL, 55% of calculated AUC24 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 AUC24 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.