To clarify whether the new Japanese glomerular filtration rate (eGFR) equation was able to accurately determine the initial and individualized dosage adjustment concentrations of vancomycin (VCM), the predictive performance for VCM concentrations using the eGFR and Cockcroft-Gault (CG) equations was compared. Data were retrospectively collected from clinical records of 90 patients with MRSA infection whose trough and peak VCM concentrations had been determined. The predicted VCM initial and individualized dosage adjustment concentrations were performed with the 2-compartment linear model using pharmacokinetic parameter means and their individual values via Bayesian estimation, respectively. The prediction error (PE) and its absolute value (APE) between the observed and predicted VCM concentrations were calculated as indices of bias and accuracy in predictive performance, respectively. In the initial dosage adjustment of VCM, the PE value, calculated with the eGFR equation in trough and peak VCM concentrations of patients whose BMI were 18.5 kg/m(2) and higher, was significantly smaller than that calculated with the CG equation. In particular, both PE and APE values obtained from the eGFR calculated concentrations from nonelderly patients (younger than 65 years old) were significantly improved compared with those from the CG equation. In the individualized dosage adjustment of VCM, the eGFR equation gave a significantly smaller PE value in nonelderly patients' trough concentrations than the CG equation. These findings provide useful information for adjusting the VCM dosage to achieve optimal therapeutic efficacy in patients with MRSA infection.