Effects of quinapril on angiotensin converting enzyme and plasma renin activity as well as pharmacokinetic parameters of quinapril and its active metabolite, quinaprilat, after intravenous and oral administration to mature horses.

This study evaluates the effects of quinapril, a drug used for treating cardiovascular and kidney ailments in humans and small animals, in horses. The researchers sought to understand how this drug impacts equine health, specifically looking at its effects on the enzymes involved in regulating blood pressure and how it is processed in the body of horses.

Study Objective and Design

• The objective of the study was to understand the pharmacokinetics – how the drug moves through the body – of quinapril, and to observe its effects on angiotensin converting enzyme (ACE) and renin, two components important in blood pressure regulation, in horses.
• The study employed a 3-way crossover design, where six healthy mature horses were given quinapril in three different manners – 120mg intravenous, 120mg oral, and 240mg oral.
• The horses’ blood was then tested for quinapril and its active metabolite, quinaprilat, using ultra-high pressure liquid chromatography with mass spectrometry, a method that separates and identifies these substances.
• The blood samples were also tested for ACE and renin activity, using a method known as radioenzymatic assay.
• The researchers also undertook noncompartmental pharmacokinetic modelling and statistical analyses.

Study Results and Conclusion

• No adverse effects were noted in the horses during the study period. Both intravenous and oral administration of quinapril significantly inhibited the ACE activity, and renin concentrations also increased, although not significantly.
• In terms of pharmacokinetic parameters, the average terminal half-life (the time taken for the drug’s concentration in the body to be halved) was 0.694 hours for quinapril and 1.734 hours for quinaprilat, its active metabolite, following intravenous administration.
• The average volume of distribution (how far the drug spreads throughout the body) and clearance (how quickly the drug is eliminated from the body) for quinapril were also reported.
• After oral administration, quinaprilat was detected in all horses; however, its concentration was below the assay’s limit of quantification (the smallest amount that can be quantitively determined) in most horses in the 120mg dosing group.
• Despite low plasma concentrations, the study concluded that quinapril had enough oral absorption to inhibit ACE in healthy horses.
• The researchers suggested that further controlled studies be carried out in horses with real clinical conditions, as quinapril may serve as a potential treatment alternative for horses with cardiovascular and renal disease.