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) 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 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 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 was normally distributed ( = 0.096 ± 0.046 1/h); t ranged from 3 to 30 h. For target AUC = 400-600 h × μg/mL, 55% of calculated AUC results were within target. Imprecision for calculated 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 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.