Pharmacotherapeutic group: Cardiovascular system, ACE inhibitors, plain, benazepril. ATCvet code: QC09AA07
Benazepril hydrochloride is a prodrug hydrolysed in vivo to its active metabolite, benazeprilat.
Benazeprilat is a highly potent and selective inhibitor of ACE, thus preventing the conversion of inactive angiotensin I to active angiotensin II and thereby also reducing synthesis of aldosterone. Therefore, it blocks effects mediated by angiotensin II and aldosterone, including vasoconstriction of both arteries and veins, retention of sodium and water by the kidney and remodelling effects (including pathological cardiac hypertrophy and degenerative renal changes).
The product causes long-lasting inhibition of plasma ACE activity in dogs, with more than 95% inhibition at peak effect and significant activity (>80%) persisting 24 hours after dosing.
The product reduces the blood pressure and volume load on the heart in dogs with congestive heart failure.
After oral administration of benazepril hydrochloride, peak levels of benazepril are attained rapidly (Tmax 0.5 hour) and decline quickly as the active substance is partially metabolised by liver enzymes to benazeprilat. The systemic bioavailability is incomplete (~13%) due to incomplete absorption (38%) and first pass metabolism.
Peak benazeprilat concentrations (Cmax of 30 ng/ml after a dose of 0.5 mg/kg benazepril hydrochloride) are achieved with a Tmax of 1.5 hours.
Benazeprilat concentrations decline biphasically: the initial fast phase (t1/2=1.7 hours) represents elimination of free drug, while the terminal phase (t1/2=19 hours) reflects the release of benazeprilat that was bound to ACE, mainly in the tissues.
Benazepril and benazeprilat are extensively bound to plasma proteins (85-90%), and in tissues are found mainly in the liver and kidney.
There is no significant difference in the pharmacokinetics of benazeprilat when benazepril hydrochloride is administered to fed or fasted dogs. Repeated administration of the product leads to slight bioaccumulation of benazeprilat (R=1.47 with 0.5 mg/kg), steady state being achieved within a few days (4 days).
Benazeprilat is excreted 54% via the biliary and 46% via the urinary route. The clearance of benazeprilat is not affected in dogs with impaired renal function and therefore no adjustment of the product dose is required in cases of renal insufficiency.