Pharmacokinetics and pharmacodynamics of intravenous medetomidine in the horse.

The study describes the behavior and bodily effects of intravenous medication, medetomidine, on horses, alongside the drug’s pharmacokinetics, or how the body responds to and metabolizes the drug.

Objective and Methodology

• The research was a prospective experimental trial conducted on eight healthy, mature horses with an average age of 11.7 years.
• Medetomidine, in a bolus dose, was administered intravenously to the horses and blood samples were taken at fixed points. This was done from before drug administration until 48 hours post-administration.
• Researchers also documented behavioral, physiological, and biochemical data at predetermined times, from zero to 24 hours post-administration.
• To measure pain thresholds, an algometer was used. This tool can measure the horse’s responses to pain-inducing stimuli.
• Medetomidine concentration in the blood samples was calculated using liquid chromatography-Mass Spectrometry and noncompartmental and compartmental analysis.

Results

• Medetomidine showed peak concentration in the bloodstream around 6.4 minutes after administration.
• The last detection of the drug was at approximately 165 minutes post administration.
• The drug had a clearance rate of 39.6 mL kg(-1) minute(-1) and a volume of distribution of 1854 mL kg(-1).
• The elimination half-life of the drug was approximately 29.1 minutes.
• The glucose concentration in the horses increased to a maximum of about 176 mg dL(-1) roughly 1 hour after administration.
• A decrease was observed in heart rate, respiratory rate, borborygmi (rumbling or gurgling noise in the stomach), packed cell volume, and total protein concentration post drug administration.
• Behavioral changes were also documented, including the lowering of the horses’ heads and decreased mobility following the drug administration.
• The drug had an analgesic or pain-relieving effect, as demonstrated by increased mechanical thresholds and decreased sensitivity to sound. However, this analgesic effect was short-lived, lasting only from 10 to 45 minutes after the injection.

Conclusion

• The study concludes that the behavioral and physiological effects observed post drug administration correspond with the pharmacokinetic profiles, derived from plasma medetomidine concentrations.
• A transitory increase in glucose concentration was noted following the administration of medetomidine.
• The analgesic effect of medetomidine, however, was found to have a very short duration.