Pharmacokinetics and pharmacodynamics of acepromazine in horses.

The research article presents a detailed study on the drug acepromazine and its impact on horses in terms of pharmacodynamics and pharmacokinetics, investigating the relationship between dosage and effect, as well as multiple impacts such as sedation, blood pressure, and respiration function.

Methodology

• The researchers utilized a reverse-phase high-performance liquid chromatographic assay for acepromazine, a technique specific and sensitive enough to detect the presence of the drug as low as 5 ng/ml in horse plasma.
• The electrochemical detection employed had an oxidation potential of 0.7 V.
• The team administered doses of acepromazine at 0.15mg/kg of body weight, examining multiple parameters that included blood pressure, pulse, PCV, respiration function measures, and sedation effects.

Results

• Administered intravenously, acepromazine showcased a biphasic concentration decay pattern. The alpha-phase distribution half-life was less than 3 minutes, while the beta-phase half-life varied between 50 to 150 minutes.
• Within 20 minutes of administering the drug, peak CNS effects were noted. Hemodynamic effects peaked around 100 minutes.
• Most notable was the effect on the PCV – it dropped by up to 20% in all the horses (P<0.0001).
• Statistically significant drops in systolic, diastolic, and mean blood pressures were observed while heart rates remained unchanged. Blood gas tensions and blood pH also showed no noticeable change.
• A significant sedative effect, observed via the horse’s posture and alertness, was recorded in all horses.

Findings and Implications

• Despite the diverse effects of acepromazine on the studied horses, these observed pharmacodynamic effects did not correlate well with the plasma concentration of the drug.
• These effects persisted even after the acepromazine concentration was undetectable. This led the researchers to hypothesize that these extended effects may be due to active metabolites of the drug or complex pharmacokinetic compartment influences.
• This study therefore contributes significantly to our understanding of the behavior and impacts of acepromazine on the equine body, informing further research efforts and refining its clinical application in horse medicine.