Determination of total and free voriconazole in human plasma: Application to pharmacokinetic study and therapeutic monitoring

Abstract

•Voriconazole (VCZ) is highly efficient in the treatment of invasive fungal infections. However, the therapy requires the monitoring of VCZ plasma concentration, due to a narrow therapeutic index and large inter-individual variability of pharmacokinetics of VCZ, which often exhibits nonlinearity. Total plasma concentration of VCZ does not always provide sufficient information, especially in hemato-oncology patients, who often show significant fluctuations in plasma protein concentration. Therefore, the monitoring of free drug seems crucial for a complete understanding of the ongoing antifungal therapy.•The study aimed to develop an HPLC-FLD method for the determination of total and free VCZ in clinical samples.•The analysis of total VCZ comprised the one-step samples preparation by plasma protein precipitation. The free drug was isolated from plasma by ultrafiltration. The non-specific bindings (NSB) between the drug and filter membranes were comprehensively evaluated.•The elaborated method fulfilled the validation requirements for bioanalytical methods. The ultrafiltration technique is recommended for the analysis of free VCZ, but requires a preconditioning step. Ultrafiltration was impacted with adsorption of the drug on the filter membrane, which was as high as 61–82% and was found to decrease after pretreatment of the membranes with 5% Tween 80. The method was applied for the quantification of plasma VCZ in patients undergoing antifungal therapy. Total and free VCZ concentrations ranged from 0.21 to 4.92 μg/mL and from 0.07 to 1.28 μg/mL, respectively; the mean protein binding was 47%.