Comparison of area under the concentration-time curve estimations between Practical Antimicrobial Therapeutic Drug Monitoring (PAT) versions 3 and 4 for vancomycin using two-point sampling.

Practical Antimicrobial Therapeutic Drug Monitoring (PAT) for vancomycin using Bayesian estimation is recommended for calculating the area under the concentration-time curve (AUC). In 2025, PAT was updated from version 3 to version 4, but differences in AUC estimations between these versions have not been examined. This study aimed to compare AUC estimations from both versions in the same patients. We conducted a multicenter, retrospective, observational study involving adult patients who received vancomycin treatment between September 2020 and December 2023, who underwent two-point sampling for initial TDM. AUC was calculated using both versions in three phases: 0-24 h (AUC0-24), 24-48 h (AUC24-48), and at steady state (AUCss). The sample included 894 cases. AUC values from versions 3 and 4 showed a high correlation (r = 0.947-0.964), but phase-related differences emerged. Version 4 yielded significantly lower AUC0-24 and AUC24-48 values (median: 420.7 μg h/mL vs 373.5 μg h/mL, p < 0.001; 398.9 μg h/mL vs 379.8 μg h/mL, p < 0.001), while AUCss was significantly higher in version 4 (448.4 μg h/mL vs 498.2 μg h/mL, p < 0.001). Since differences in population pharmacokinetic models can affect estimation results, clinicians should be aware that AUC estimations may vary depending on the PAT version used, and the results should be interpreted with caution.