Chiral LC-MS/MS method for the simultaneous determination of (R,S)-ketamine, (R,S)-norketamine, and...

A convenient LC-MS/MS assay method to simultaneously and sensitively determine (R,S)-ketamine (Ket), (R,S)-norketamine (NK), and (2R,6R;2S,6S)-hydroxynorketamine (HNK) enantiomers in plasma and brain from mice was developed. This method enables the chiral separations of these six enantiomers in one analysis by constructing a column-switching system composed of one achiral column and two chiral columns with a relatively short analysis time (17 min). The chromatography involves the separation of (2R,6R;2S,6S)-HNK from (R,S)-Ket and (R,S)-NK on an octadecyl-silica column, followed by chiral separations on a CHIRALPAK AY-RH column for (2R,6R;2S,6S)-HNK or on a CHIRALPAK AS-RH column for the other analytes. The calibration curves for plasma and brain showed a good linearity in the range of 3-1000 ng/mL and 1.5-500 ng/g, respectively. The accuracy ranged from 90.0% to 104.0% in within-run and between-run. This validated method was applicable to determine the stereoselective pharmacokinetic profiles of (R,S)-Ket, (R,S)-NK, and (2R,6R;2S,6S)-HNK in plasma and brain collected from individual mice after a single intraperitoneal dosing of racemic Ket at an antidepressant dose. It is hoped that this assay will greatly help for understanding the relationship between the antidepressant actions of (R,S)-Ket enantiomers or their metabolites and their pharmacokinetics.