UPLC-MS/MS determination of flavokawain B, a novel anti-tumor chemotherapeutic agent in rat plasma and its application to a pharmacokinetic study in rats.

A sensitive, selective and rapid ultra-performance liquid chromatography/tandem mass spectrometry method was developed and validated for the quantification of flavokawain B in rat plasma using myrislignan as an internal standard. Sample preparation was accomplished through a protein precipitation extraction process. Chromatographic resolution of flavokawain B and the IS was achieved on an Agilent XDB-C18 column (2.1 × 100 mm, 1.8 μm) using a gradient mobile phase comprising 0.1% formic acid in water and acetonitrile delivered at a flow rate of 0.5 mL/min. Flavokawain B and the IS eluted at 3.27 and 1.96 min, respectively. The total chromatographic run time was 6.0 min. A linear response function was constructed in the concentration range 0.524-1048 ng/mL. Method validation was performed as per the US Food and Drug Administration guidelines and the results met the acceptance criteria. Intra- and inter-day accuracy and precision were in the ranges of -14.3-13.2 and 3.4-11.8%, respectively. Flavokawain B was demonstrated to be stable under various stability conditions. This method has been applied to a pharmacokinetic study in rats.