Evaluation of the association between trough and area under the curve to minimum inhibitory concentration ratio(AUC24/MIC) of vancomycin in infected patients with MRSA

Background: The recent studies emphasized on the correlation of vancomycin antibacterial effect with pharmacokinetics properties such as the area under the curve/minimum inhibitory concentration (AUC/MIC) ≥400 and serum trough level 15-20 mg /dl in the patients with severe infection with methicillin-resistant Staphylococcus aureus (MRSA). The purpose is to assay the vancomycin pharmacokinetic properties in our population and evaluates the correlation between AUC/MIC and trough serum level of vancomycin in given patients. Method: The inpatients with a positive MRSA culture, treated with vancomycin, were enrolled in this cross-sectional study. Three plasma samples were obtained during the study including 30 min before fourth and the fifth dose as trough levels and 1 hour after the fourth dose as peak level to determine AUC. E-TEST determined the MIC of vancomycin. Result: 38 patients with average age of 48.33 (SD 16.44) were enrolled in this study. The mean ± SD of MIC was reported as 0.99±0.30 mg/L. 34 patients reached the adequate therapeutic range of AUC/MIC ≥ 400 due to the standard vancomycin dosing method. In comparison, only 7 and 10 patients had the first and second trough levels in target intervals of 15-20 mg/dl, respectively. Due to the receiver operating characteristic curve test (ROC test), the trough level after the fourth dose had a strong correlation with target AUC/MIC with a sensitivity of 94.10% and specificity of 75.00%. Conclusion: This study concluded using only a trough level is not appropriate for therapeutic drug monitoring (TDM) of the vancomycin. In our population, target AUC/MIC (≥ 400) had a reasonably strong correlation with the trough level before the fifth dose which achieved with trough level ≥10.81 mg/dl and MIC< 1 mg/L.