• Takenori Niioka, Naohito Fujishima, Maiko Abumiya, Takaya Yamashita, Kumi Ubukawa, Miho Nara, Masumi Fujishima, Naoto Takahashi, and Masatomo Miura.
• *Department of Pharmacy, Akita University Hospital; †Division of Blood Transfusion, Akita University Hospital; and ‡Department of Hematology, Nephrology and Rheumatology, Akita University Graduate School of Medicine, Akita, Japan.
• Ther Drug Monit. 2017 Oct 1; 39 (5): 514-521.

BackgroundAlthough voriconazole (VRCZ) is metabolized to VRCZ N-oxide principally by CYP2C19, VRCZ clearance is affected by multiple factors. In this study, we investigated the relationship between the CYP2C19 phenotype using the VRCZ-to-VRCZ N-oxide plasma concentration ratio (VRCZ/N-oxide) and demographic and clinical characteristics of Japanese patients taking VRCZ.MethodsA total of 65 Japanese patients taking VRCZ for prophylaxis or treatment of fungal infection were enrolled in this study. Stepwise selection multiple linear regression analysis was performed to investigate the effect of factors on the VRCZ/N-oxide ratio.ResultsIn patients not undergoing concurrent treatment with a drug influencing CYP2C19 activity (n = 54), the VRCZ/N-oxide ratio with definite thresholds for CYP2C19 genotypes, CYP2C19*1/*1, *1/*2 + *1/*3 + *2/*17, and *2/*2 + *2/*3, was specifically identified in patients taking VRCZ (<0.48, ≥0.48 < and <0.82 and ≥0.82). However, the VRCZ/N-oxide ratio could not be predicted based solely on the CYP2C19 genotype (R = 0.053). The route of VRCZ administration, C-reactive protein concentration determined on the same day as VRCZ plasma concentration measurement, CYP2C19 extensive metabolizer, and patient age were independent factors influencing the VRCZ/N-oxide ratio (R = 0.489, standardized regression coefficient = 0.385, 0.380, -0.231, and 0.231; P = 0.001, 0.001, 0.032, and 0.036, respectively).ConclusionsIt is possible to comprehensively evaluate CYP2C19 activity using the actual measured value of the VRCZ/N-oxide ratio in patients taking VRCZ. The predictive performance of the VRCZ/N-oxide ratio was improved by including the route of administration, C-reactive protein level, and patient age in addition to the CYP2C19 genotype as predictive factors.

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