The aim of this study was to develop and validate a novel bioassay for determining serum voriconazole (VRC) concentrations and to compare its routine clinical performance with that of high-performance liquid chromatography (HPLC). The biological activity of VRC was measured by a plate diffusion assay using a VRC-hypersusceptible Candida kefyr strain. The bioassay's utility was tested by measuring steady-state VRC concentrations in 100 serum probes from VRC-treated patients. The HPLC system used solvent extraction with hexane:dichloromethane followed by reversed-phase HPLC with ultraviolet detection. The intra-day and inter-day accuracy of the bioassay was <5%, while that of HPLC was <1%. The precision (mean coefficient of variation, 3.5%) was equal for both the methods. The limit of quantification was lower for HPLC (0.2 mg l(-1)) than for the bioassay (0.5 mg l(-1)). The result of linear regression analysis was HPLC = 1.0178 (bioassay) + 0.328; R(2) = 0.88; n = 100. Results of the serum panel ranged from 0.5 to more than 8.0 mg l(-1) for the bioassay and from 0.26 to 10.1 mg l(-1) for HPLC. Especially in laboratories without access to HPLC, the bioassay may be a clinically useful tool for therapeutic drug monitoring.
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