Characterization of the stereoselective biotransformation of ketamine to norketamine via determination of their enantiomers in equine plasma by capillary electrophoresis.

The research study demonstrates a reliable laboratory process, using capillary electrophoresis, for detecting different forms of the drugs ketamine and norketamine in horse blood. The study also reveals how the body metabolizes ketamine differently based on the presence of another drug, xylazine.

Method Description

• The research outlines a robust analytical method, known as capillary electrophoresis (CE), for the simultaneous detection of the enantiomers (mirror-image forms) of ketamine and norketamine in equine plasma (horse blood).
• This method is based on liquid-liquid extraction of ketamine and norketamine at alkaline pH from 1 milliliter of plasma. This is followed by an analysis of the reconstituted extract using CE.
• The CE process uses a pH 2.5 Tris-phosphate buffer containing 10 mg/mL of highly sulfated beta-CD (a type of carbohydrate molecule) as the chiral selector, which separates different forms of a molecule based on their shape.
• The method’s sensitivity allows detection of enantiomer plasma levels between 0.04 and 2.5 micrograms per mL.
• Accuracy checks showed that the method identifies ketamine consistently, with only small variations in results when tested multiple times across different days.

Testing the Method

• This method was validated on plasma samples from ponies under isoflurane anesthesia and ponies premedicated with xylazine, as well as a horse that received several medications.
• The researchers delivered a dose of 2.2 milligrams per kilogram of racemic ketamine (a mixture containing equal amounts of two enantiomers) to the animals.

Findings

• The study found that the ketamine’s biotransformation process (how the body breaks down the drug) is stereoselective (preferential to one type of enantiomer over another) unless xylazine is present.
• In the absence of xylazine, S-norketamine levels in plasma were higher than R-norketamine levels. Norketamine is a metabolite, a substance the body produces when it breaks down ketamine.
• However, for the group premedicated with xylazine, this stereoselectivity was not observed.