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.