CE provides evidence of the stereoselective hydroxylation of norketamine in equines.

The research article investigates the stereoselective hydroxylation of norketamine in equines. It utilizes CE with multiple isomer sulfated-CD to analyze the stereoisomers of ketamine and its metabolites, as well as hydroxylated norketamine metabolites in equine liver microsomes. The results show a major metabolic pathway in equines being the demethylation of ketamine followed by hydroxylation of norketamine at the cyclohexanone ring, with the process being highly stereoselective.

Use of CE with Multiple Isomer Sulfated-CD

• The research made use of Capillary Electrophoresis (CE) in combination with multiple isomer sulfated-CD. This was for the simultaneous analysis of different stereoisomers that include ketamine, norketamine, 5,6-dehydronorketamine as well as the hydroxylated metabolites of norketamine. The metabolites were extracted from the in vitro incubations with ketamine or norketamine and equine liver microsomes.
• CE method was also utilized in the analysis of the plasma and urine of ponies that were given a target-controlled infusion of ketamine under isoflurane anesthesia, providing insight into the metabolism of ketamine in live equine subjects.

Formation of Hydroxynorketamine Metabolites

• Hydroxynorketamine metabolites form with a hydroxy group at the cyclohexanone ring. The research showed that these metabolites are formed stereoselectively, meaning they produce one steroisomer preferentially over the other, both in vitro and in vivo.
• Characterization of collected fractions from urinary extracts, shared through HPLC (High Performance Liquid Chromatography), was followed by the use of CE and LC-MS(n) with 0.7 mmu mass discrimination for further identification.

Identification of Metabolites

• Comparison of LC-MS(n) data from the urinary fractions, in vitro microsomal sample, and pony urine led to the identification of various hydroxylated norketamine and ketamine metabolites. However, due to lower detection sensitivity, only four hydroxynorketamine metabolites with hydroxylation at the cyclohexanone ring were observed by CE.
• The findings suggest that the major metabolic pathway in equines begins with the demethylation of ketamine, followed by hydroxylation of norketamine at the cyclohexanone ring. This metabolism process was found to be highly stereoselective.