Therapeutic Drug Monitoring of Voriconazole: Comparison of Bioassay with High-Performance Liquid Chromatography

Background Voriconazole is a triazole antifungal agent with considerable inter and intra-individual variability in plasma concentrations. Therapeutic drug monitoring of voriconazole plays an important role in optimizing the efficacy and safety of the drug in patients. Objectives This study aimed at evaluating the performance of a simple agar well diffusion bioassay and comparing its utility with high-performance liquid chromatography (HPLC). Methods The clinical isolate of voriconazole hyper susceptible Candida kefyr was used for a simple agar well diffusion bioassay method. Acetonitrile precipitations followed by reverse-phase HPLC on C18 column, with ultra violet detection, were used for HPLC. Cross validation was done by evaluating the accuracy and precision of both methods in a large cohort of 180 samples from 60 voriconazole-treated patients. Results The validated bioassay method and HPLC, as a reference method, were found to be accurate and precise. A good correlation was found between the 2 methods with similar analytical range (0.25 – 16 µg/mL). The result of linear regression analysis revealed bioassay = 0.961 (HPLC) +0.148; R² = 0.965; correlation coefficient = 0.982; n = 180. Voriconazole serum concentration of patients ranged from 0.25 µg/mL to 5.41 µg/mL when using HPLC, and from 0.25 µg/mL to 5.71 µg/mL when using the bioassay method. Conclusions When laboratories are not equipped with HPLC, bioassay may be a reliable technique with sufficient accuracy and precision for monitoring voriconazole plasma concentration.