Are All Pharmacokinetic Equations Created Equal? A Comparative Analysis of Trapezoidal and Non-Trapezoidal Methods for Estimating Day 1 Area Under the Curve in Adult Hospitalized Patients with Staphylococcus aureus Bacteremia

This study compared the calculated vancomycin area under the curve (AUC 0–24 ) using trapezoidal and non-trapezoidal first-order pharmacokinetic equations. This retrospective observational study included adult patients with documented MRSA bacteremia who received ≥ 48 h of intravenous vancomycin and had two consecutive serum levels after the first dose. AUC 0–24 was calculated using trapezoidal and non-trapezoidal equations. Correlation and agreement between methods were assessed using Pearson’s correlation coefficient ( r ) and Bland–Altman plots. Significant predictors ( p < 0.05) from simple linear regression were included in a multiple linear regression model to evaluate their impact on AUC 0–24 for both methods. Fifty-two patients were included. The median age was 63 years (interquartile range [IQR]: 50–73), and the median vancomycin clearance was 4 l/h (IQR: 2–6). Median vancomycin AUC 0-24 was 399 mg∙h/l (IQR: 257–674) for the trapezoidal method and 572 mg∙h/l (IQR: 466–807) for the non-trapezoidal method. There was a strong correlation between the methods ( r = 0.87 [95% CI, 0.79–1]; P < 0.01), but Bland–Altman analysis showed poor agreement, with a bias of – 198 mg∙h/l and 95% limits of agreement from – 482 to 86 mg∙h/l. In multiple linear regression, total daily dose and vancomycin clearance were independent predictors of AUC 0–24 for both methods, with a stronger impact on non-trapezoidal AUC 0-24 (adjusted R 2 = 0.70) than trapezoidal AUC 0–24 (adjusted R 2 = 0.59). Trapezoidal and non-trapezoidal equations are not interchangeable for estimating vancomycin AUC 0–24 . The trapezoidal method consistently results in lower AUC 0–24 estimates than the non-trapezoidal method.