Enantioselective determination of ketamine in dog plasma by chiral liquid chromatography-tandem mass spectrometry.

ABSTRACT

Ketamine is an N-methyl-d-aspartate receptor antagonist that is usually used clinically as a racemic mixture. Its two enantiomers exhibit different pharmacological activities. To determine whether the enantiomers have different pharmacokinetic profiles, a chiral liquid chromatography-tandem mass spectrometry method was developed and validated for the determination of ketamine enantiomers in dog plasma. The enantiomers of ketamine were extracted from 50 µL of plasma by methyl tert-butyl ether. Adequate chromatographic retention and baseline resolution of the enantiomers were achieved within a runtime of 5 min on a chiral column coated with polysaccharide derivatives, using a gradient mobile phase of acetonitrile and 10 mm ammonium bicarbonate aqueous solution. Ketamine enantiomers were detected by mass spectrometry with multiple reaction monitoring mode using the transitions of m/z 238.3 → 125.9 for the analytes and m/z 237.1 → 194.1 for carbamazepine (internal standard). The method was linear over the concentration range from 0.5 to 500 ng/mL for each enantiomer. The lower limit of quantification (LLOQ) for each enantiomer was 0.5 ng/mL. The intra- and inter-day precision was <7.3% and 8.5% for R- and S-ketamine, respectively. The accuracy was 92.9-110.4% for R-ketamine and 99.8-102.4% for S-ketamine. The method was successfully applied to characterize the stereoselective pharmacokinetic profiles of ketamine in beagle dogs.