Quantitative determination of regorafenib and its two major metabolites in human plasma with high-performance liquid chromatography and ultraviolet detection

A simple, highly sensitive and specific high-performance liquid chromatography (HPLC) method was developed for the simultaneous quantitation of regorafenib, N-oxidemetabolite (M-2) and the desmethyl N-oxide metabolite (M-5) in human plasma. Regorafenib, M-2, M-5 and the internal standard sorafenib were separated using a mobile phase of 0.5% KH2 PO4 (pH 3.5)-acetonitrile (30:70, v/v), on a Capcell PAK MG II column at a flow rate of 0.5 mL/min and measurement at UV 260 nm. The lower limits of quantification for regorafenib, M-2 and M-5 were 10 ng/mL for each analyte. A procedure using solid-phase extraction required only a small amount of plasma (100 μL) for one analysis while providing high extraction recovery (>81% for all compounds) and good selectivity. Coefficients of variation for intra- and inter-day assays were <12.2% for regorafenib, <12.3% for M-2 and <15.1% for M-5. Accuracies for intra- and inter-day assays were <9.4% for regorafenib, <8.0% for M-2 and <12.8% for M-5 over a linear range from 10 to 10,000 ng/mL. This HPLC assay is suitable for clinical pharmacokinetic studies of regorafenib. The present HPLC method is currently in use for our observational studies of patients under treatment. Copyright © 2016 John Wiley & Sons, Ltd.