Clinical Evaluation of a Two-Point First-Order Pharmacokinetic Method for Vancomycin Therapeutic Drug Monitoring

Background: This study aims to validate the two-point first-order pharmacokinetic (PK) method for vancomycin therapeutic drug monitoring (TDM) by comparing it to the two-point Bayesian method for potential clinical implementation.Methods: Since September 2023, a two-point (trough and peak) first-order PK method has been implemented in a secondary teaching hospital for vancomycin monitoring.Only cases in which vancomycin was administered at least three times were included in the study.All interpretation reports were cross-validated using the web-based two-point Bayesian method program, TDMx.A retrospective review of all vancomycin monitoring reports over 1 year was conducted to compare estimations from both methods.Results: A total of 34 vancomycin monitoring reports were submitted for 21 inpatients.One case submitted before reaching steady state was excluded.The mean difference in expected area under the curve over 24 hr (AUC24) between the two methods was 0.2% (-16.1% to 16.4%) at the current dose and -3.1% (-18.5% to 8.2%) at the recommended dose.Compared with the Bayesian method, the first-order PK method showed discrepancies in two cases regarding optimality: one where the estimated half-life exceeded 24 hr and another where monitoring was performed after the third dose following a dose adjustment.At the recommended dose, no differences in optimality were found between the two methods.Conclusions: The first-order PK method produced reliable results in 93.9% of cases compared with the Bayesian method.However, caution is necessary, especially when fewer than four doses have been administered or when the estimated half-life exceeds 24 hr.