Quantification of the Plasma Concentration of Vadadustat by High-Performance Liquid Chromatography with Ultraviolet Detection and Ultra-Performance Liquid Chromatography-Tandem Mass Spectrometry

Background: An inexpensive, simple, and accurate plasma concentration measurement system is needed to actively conduct pharmacokinetic and pharmacodynamic analyses of vadadustat, hypoxia-inducible factor-prolyl hydroxylase inhibitor, in clinical settings. In this study, the authors aimed to develop a method for measuring vadadustat in human plasma that could be applied for therapeutic drug monitoring using high-performance liquid chromatography with ultraviolet detection (HPLC-UV) in a clinical setting. Methods: Plasma samples (100 mu L) were pretreated with acetonitrile using butyl paraoxybenzoate as an internal standard. Chromatographic separation was performed on a SunShell PFP C18 column (2.6 mu m, 4.6 mm x 150 mm). The mobile phase consisted of (A) 20 mM of phosphate buffer (pH 2.4) and (B) acetonitrile (60:40, v/v), delivered isocratically at a flow rate of 1 mL/min. The analytes were detected by UV absorbance at a wavelength of 220 nm, and the column temperature was 40 degrees C. To evaluate the applicability of HPLC-UV in a clinical setting, blood samples were collected at 19 time points from 7 patients who had been taking vadadustat. Results: The calibration curve was linear over the concentration range of 0.2-150 mcg/mL (R2 > 0.99). Intra-assay and interassay accuracy, precision, and stability met the Food and Drug Administration recommendations. The vadadustat plasma concentrations of patients analyzed using the current HPLC-UV method were almost equal to those measured using ultra-performance liquid chromatography-tandem mass spectrometry (mean difference: 0.13 mcg/mL). Large variability in the dose-adjusted plasma concentrations of vadadustat at 12 hours after administration was observed between patients (coefficient of variation = 57.6%). Conclusions: This HPLC-UV method is a simple, accurate quantification method for evaluating plasma concentrations in patients taking vadadustat in a clinical setting.