Prospective Analysis of Factors Influencing Inter-Individual Variation in Trough Plasma Voriconazole Concentrations in Older Patients—Impact of High <i>α</i>1-Acid Glycoprotein Levels

Voriconazole (VRCZ), an azole-based, deep-seated antifungal agent, is used as a 1st-line treatment for aspergillosis in Japan. VRCZ exhibits nonlinear pharmacokinetic (PK) behavior with relatively large inter-individual variability in plasma concentration. Additionally, genetic polymorphisms of CYP2C19 have been reported to influence the metabolic variability of VRCZ. The purpose of this study was to search for and identify clinically relevant potential factors influencing the PK and plasma concentration of VRCZ to better inform VRCZ dosing regimens. Thirty patients receiving VRCZ were enrolled. Total (C_t) and unbound (C_u) trough plasma concentrations of VRCZ were determined by the HPLC-UV method. Univariate and multivariate correlation analyses were used to evaluate the relationships between C_t or C_t/dose per body weight (C_t/D) and individual demographic and laboratory characteristics. Since the increasing trend of C-reactive protein (CRP) inversely correlated with the classification of CYP2C19 gene polymorphisms, it was suggested that the inflammation counteracted the trend of C_t according to CYP2C19 gene polymorphisms. Spearman's rank-order correlation analysis showed significant correlations between C_t and dose per body weight, CRP, and α1-acid glycoprotein (α1-AGP). Multivariate linear regression analysis showed that age, dose per body weight, CRP, and α1-AGP were significant explanatory factors for C_t. In particular, elevated α1-AGP levels were found to have significant explanatory value for decreased C_t. Although the present study has critical limitations, such as the patient sample was small in size and being limited to a single medical institution, this finding may explain some of the inter-individual variability in plasma VRCZ concentration.