BACKGROUND: It has been reported that the protein binding rate of vancomycin (VCM) varies among individual patients. So, the authors investigated relevant factors that may affect free VCM concentration and target attainment of free area under the concentration-time curve (fAUC). METHODS: Thirty-nine patients were included. Multiple regression analysis was performed to determine the valuable factors in the free VCM concentration, and the target attainment of area under the concentration-time curve (AUC) 400-600 mg・h/L and fAUC200-300 mg・h/L was calculated. RESULTS: We found total protein was significant covariate for free VCM. Among 18 patients who were investigated for AUC and fAUC estimation, 9 patients (50.0%) and 12 patients (66.7%) reached AUC >
600 mg・h/L, and fAUC >
300 mg・h/L (p = 0.310), respectively. CONCLUSIONS: Total protein is a significant predictor for free VCM estimation. And the fAUC-guided TDM for VCM TDM may contribute to more strict dosing than the AUC-guided TDM in hyper- or hypo-proteinemic population. TRIAL REGISTRATION: Retrospectively registered.