A Prospective Study on the Usefulness of Initial Voriconazole Dose Adjustment Based on CYP2C19 Gene Polymorphism...

Genetic polymorphism exists for CYP2C19, a dominant metabolic enzyme of voriconazole (VRCZ), and VRCZ pharmacokinetics has been shown to fluctuate according to the CYP2C19 phenotype. Although dosages for different phenotypes have been recommended in various retrospective studies, few reports have adjusted the initial VRCZ dose based on CYP2C19 phenotype determined prior to administration. In this study, we prospectively evaluated the usefulness of CYP2C19 polymorphism analysis in adjusting the initial VRCZ maintenance dose. The study enrolled 19 patients who underwent analysis of CYP2C19 polymorphism prior to VRCZ administration. Subjects were classified into 3 phenotype subgroups: extensive metabolizer (EM), intermediate metabolizer (IM), and poor metabolizer (PM). The initial VRCZ maintenance doses given twice daily were proposed as follows: approximately 8, 6, and 4 mg/kg/day for EM, IM and PM, respectively, according to previous reports. In EM, the initial maintenance dose was 8.0 ± 0.5 mg/kg/day, and trough level was 6.6 ± 2.4 μg/mL. By contrast, the initial maintenance doses in IM and PM were 5.5 ± 0.7 and 4.1 ± 0.3 mg/kg/day, and the initial trough concentrations were 2.9 ± 1.2 and 2.6 ± 0.4 μg/mL, respectively. The attainment rate of target trough concentration of 1-6 μg/mL was 50% in EM, and was 100% in IM and PM. Determining the initial dose of VRCZ only by phenotype based on CYP2C19 gene polymorphism was found to be challenging. However, decreasing the initial maintenance dose in IM and PM may be important for adjusting the initial trough level to target range.