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.
Authors: Davis J L, Kruger K, LaFevers D H, Barlow B M, Schirmer J M, Breuhaus B A
Journal: Equine veterinary journal
Summary
# Editorial Summary ACE inhibitors represent a well-established therapeutic option in human and small animal medicine for managing cardiovascular and renal disease, yet their pharmacological properties and clinical efficacy in horses remain poorly characterised. Davis and colleagues administered quinapril to six healthy horses via intravenous injection and oral dosing (120–240 mg) in a crossover design, measuring drug concentrations, ACE inhibition and plasma renin activity using chromatographic and radioenzymatic techniques. Despite quinapril showing poor oral bioavailability (<5%), both intravenous and oral routes significantly suppressed ACE activity; the drug's active metabolite quinaprilat reached peak plasma concentrations of 145 ng/ml within 10 minutes of IV administration and persisted with a half-life of 1.73 hours, whilst renin concentrations increased modestly (though not significantly) across all treatment groups. The clinical significance lies in the finding that meaningful ACE inhibition occurs even at the low systemic concentrations achieved through oral dosing, suggesting quinapril warrants further investigation as a therapeutic tool in horses with cardiac or renal pathology, though controlled studies in affected animals are essential before recommendations can be made regarding optimal dosing protocols and clinical outcomes.
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Practical Takeaways
- •Quinapril may be a viable oral treatment option for horses with cardiovascular and renal disease, as ACE inhibition occurs even with low plasma concentrations
- •Current evidence is limited to healthy horses; clinical efficacy and optimal dosing protocols need to be established in horses with actual cardiovascular or renal disease before widespread adoption
- •The very short half-life of quinapril (0.694 h) and moderate half-life of its active metabolite (1.734 h) suggest multiple daily dosing may be required for sustained therapeutic effect
Key Findings
- •Both intravenous and oral quinapril significantly inhibited ACE activity in healthy horses with no adverse effects observed
- •Quinapril showed very low oral bioavailability (<5%) but still produced measurable ACE inhibition
- •Intravenous quinapril had a terminal half-life of 0.694 h while its active metabolite quinaprilat had a half-life of 1.734 h
- •Quinaprilat was detected in plasma following oral quinapril administration in all horses, despite concentrations being below quantifiable limits in most horses at the 120 mg dose