Evaluation of the Association between Trough and Area Under the Curve to Minimum Inhibitory Concentration Ratio (AUC24/MIC) of Vancomycin in Infected Patients with Methicillin Resistant Staphylococcus aureus (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 (AUC24/MIC) ≥400 and serum trough level 15-20 mg /L 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 AUC24/MIC and trough serum level of vancomycin in given patients.

Methods: The patients 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 AUC24. E-TEST determined the MIC of vancomycin.

Results: Thirty-eight patients with an average age of 48.33±16.44 were enrolled in this study. The mean ± SD of MIC was 0.99±0.30 mg/L. Thirty-four patients reached the adequate therapeutic range of AUC24/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/L, respectively. Due to the receiver operating characteristic curve test (ROC test), the trough level after the fourth dose had a strong correlation with target AUC24/MIC with a sensitivity of 94.1%and specificity of 75.0%.

Conclusion: This study concluded using only a trough level is not appropriate for therapeutic drug monitoring (TDM) of vancomycin. In our population, target AUC24/MIC (≥ 400) had a reasonably strong correlation with the trough level before the fifth dose which achieved with trough level ≥10.81 mg/L and MIC< 1 mg/L.