Simultaneous determination of idelalisib and its metabolite GS-563117 in dog plasma by LC-MS/MS: Application to a pharmacokinetic study.

The purpose of this study was to develop and validate an LC-MS/MS method for simultaneous determination of idelalisib and GS-563117 in dog plasma. The analytes were extracted using ethyl acetate and then separated on a Waters Acquity UPLC BEH C18 column (50 × 2.1 mm, i. d., 1.7 μm) using 0.1% formic acid in water and acetonitrile as mobile phase at a flow rate of 0.3 mL/min in gradient elution mode. The analytes were quantified using selected reaction monitoring with precursor-to-product transitions at m/z 416.2 → 176.1, m/z 432.2 → 192.1 and m/z 421.2 → 176.1 for idelalisib, GS-563117 and [2 H5 ]-idelalisib (internal standard). The assay showed good linearity (r > 0.9992) over the tested concentration range of 0.1-600 ng/mL for idelalisib and 0.1-300 ng/mL for GS-563117. The intra- and inter-day RSD values for idelalisib and GS-563117 were <8.84 and 12.41%, respectively. The intra- and inter-day RE values were within the range of -7.21-8.52%, and -6.44-14.23%, respectively. The extraction recovery was found to be >84.59% and no matrix effects were observed. The validated LC-MS/MS method has been successfully applied for the simultaneous determination of idelalisib and GS-563117 in a pharmacokinetic study in dogs. Our results suggested that idelalisib was rapidly metabolized into its metabolite GS-563117 in dog and the in vivo exposure of GS-563117 was 17.59% of that of idelalisib.