Stereoselective pharmacokinetics of ketamine and norketamine after racemic ketamine or S-ketamine administration in Shetland ponies sedated with xylazine.

The research article investigates the differences in how the bodies of sedated Shetland ponies process two versions of ketamine (racemic ketamine and S-ketamine) and its metabolite, norketamine. The researchers also measured how long it took the ponies to recover from the sedation.

Study Design

In the study, ketamine and norketamine’s pharmacokinetics were studied in five Shetland ponies. The ponies were sedated with xylazine, then given either intravenous raemic ketamine or S-ketamine. Pharmacokinetics is a branch of pharmacology that studies how an organism affects a drug. Studied parameters here encompass how fast and how completely the bodies of the ponies absorbed, distributed, biotransformed, and eliminated the drugs.

• The ponies’ recovery from sedation was also tracked by noting the time intervals they took to resume sternal (lying on their chest) and standing positions.
• Arterial blood samples were drawn at several intervals before and after the administration of ketamine for testing.
• Arterial blood gases were also evaluated five minutes post-injection for hypoxia (low oxygen) and hypercarbia (excessive carbon dioxide), reflecting the ponies’ respiratory responses to ketamine.

Results Interpretation

The tests performed on the blood samples revealed differences in how the ponies’ bodies processed the two different versions of ketamine.

• The S-ketamine was eliminated from the body more quickly than the racemic ketamine, indicated by a significantly higher elimination rate constant for the former. Thus, the half-life (the time it takes for half the drug to be eliminated from the body) and mean residence time (average time the drug molecule is in the body) were shorter for S-ketamine than for racemic ketamine.
• The maximum concentration of S-norketamine, a metabolite of ketamine, was higher after S-ketamine administration, indicating a greater conversion rate of S-ketamine to S-norketamine.
• The ponies recovered faster from the sedation after receiving S-ketamine compared to racemic ketamine, as evident from the significantly shorter time they took to return to a standing position.
• The evaluation of blood gases showed signs of mild hypoxaemia and hypercarbia after ketamine injection. These indications suggest a minor impact of the drugs on the ponies’ respiratory function.

Through these findings, the study provides useful insights into the varied impacts of different forms of ketamine on the body of sedated ponies. This information may have significant implications for veterinary anesthesia and post-surgery monitoring protocols.