Pharmacokinetics and pharmacodynamics of detomidine following sublingual administration to horses.

The study documents the analysis of the effects, detection, and elimination of the drug detomidine in the system after it’s been administered to horses. The aim is to help establish the necessary withdrawal time before competition and ensure the welfare of the animal.

Methods Used in the Research

• The research was carried out on 12 adult racehorses, where each received a single sublingual administration of 0.04 mg of detomidine/kg.
• Blood and urine samples were collected from the horses at specific intervals to determine the concentration of the drug and its metabolites in their system.
• The blood samples were collected before the detomidine administration and for up to 72 hours afterward.
• Urine samples were instead taken for 5 days after the drug administration.
• These samples were then analyzed using liquid chromatography-mass spectrometry, a technology that enables the separation and quantification of substances within a sample.
• Apart from sample collection, several physiological parameters were also monitored after detomidine administration. These included chin-to-ground distance, heart rate and rhythm, glucose concentration, packed cell volume (PCV), and plasma protein concentration.

Findings of the Research

• The study found that the mean terminal elimination half-life of detomidine was approximately 1.5 hours. In simpler terms, detomidine’s concentration in the body decreases by half every 1.5 hours.
• By 24 hours post-administration, concentrations of detomidine and its metabolites in the plasma were minimal and below the detection limit.
• In urine, detomidine and its metabolites were undetectable by the third day after administration.
• Immediately after administration, the horses showed varying degrees of sedation. The onset was within 40 minutes, and the sedation lasted around 2 hours.
• Physiological parameters also changed with detomidine administration. There were significant decreases in the horses’ chin-to-ground distance and heart rate, and an increased incidence of preexisting atrioventricular blocks, which indicate disruptions in heart rhythms.

Conclusion of the Study

• Based on the research findings, it is recommended that a 48-hour and 3-day withdrawal period should be followed for detection in plasma and urine samples, respectively, after the sublingual administration of detomidine gel to horses.
• This withdrawal period ensures that the drug and its metabolites are no longer detectable in the system before the horse participates in a competition. It safeguards both the fairness of the competition and the welfare of the horse.