Single and multiple doses of 10 mg or more of benazepril cause inhibition of plasma ACE activity by at least 80% to 90% for at least 24 hours after dosing. Pressor responses to exogenous angiotensin I were inhibited by 60% to 90% (up to 4 hours post-dose) at the 10 mg dose.
Benazepril has been used concomitantly with beta-adrenergic-blocking agents, calcium-channel-blocking agents, diuretics, digoxin, and hydralazine, without evidence of clinically important adverse interactions. Benazepril, like other ACE inhibitors, has had less than additive effects with beta-adrenergic blockers, presumably because both drugs lower blood pressure by inhibiting parts of the renin-angiotensin system.
The pharmacokinetics of benazepril are approximately dose-proportional within the dosage range of 10 to 80 mg.
Following oral administration of benazepril, peak plasma concentrations of benazepril, and its active metabolite benazeprilat are reached within 0.5 to 1 hours and 1 to 2 hours, respectively. While the bioavailability of benazepril is not affected by food, time to peak plasma concentrations of benazeprilat is delayed to 2 to 4 hours.
The serum protein binding of benazepril is about 96.7% and that of benazeprilat about 95.3%, as measured by equilibrium dialysis; on the basis of in vitro studies, the degree of protein binding should be unaffected by age, hepatic dysfunction, or concentration (over the concentration range of 0.24 to 23.6 μmol/L).
Benazepril is almost completely metabolized to benazeprilat by cleavage of the ester group (primarily in liver). Both benazepril and benazeprilat undergo glucuronidation.
Benazepril and benazeprilat are cleared predominantly by renal excretion. About 37% of an orally administered dose was recovered in urine as benazeprilat (20%), benazeprilat glucuronide (8%), benazepril glucuronide (4%) and as trace amounts of benazepril. Nonrenal (i.e., biliary) excretion accounts for approximately 11% to 12% of benazeprilat excretion. The effective half-life of benazeprilat following once daily repeat oral administration of benazepril hydrochloride is 10 to 11 hours. Thus, steady-state concentrations of benazeprilat should be reached after 2 or 3 doses of benazepril hydrochloride given once daily.
Accumulation ratio based on AUC of benazeprilat was 1.19 following once daily administration.
The pharmacokinetics of systemic exposure to benazepril and benazeprilat in patients with mild-to-moderate renal insufficiency (creatinine clearance > 30 mL/min) is similar to that in patients with normal renal function. In patients with creatinine clearance ≤ 30 mL/min, peak benazeprilat levels and the initial (alpha phase) half-life increase, and time to steady-state may be delayed [see Dosage and Administration (2)].
When dialysis was started 2 hours after ingestion of 10 mg of benazepril, approximately 6% of benazeprilat was removed in 4 hours of dialysis. The parent compound, benazepril, was not detected in the dialysate.
In patients with hepatic insufficiency (due to cirrhosis) , the pharmacokinetics of benazeprilat are essentially unaltered.
The pharmacokinetics of benazepril are not affected by the following drugs: hydrochlorothiazide, furosemide, chlorthalidone, digoxin, propranolol, atenolol, nifedipine, amlodipine, naproxen, acetylsalicylic acid, or cimetidine. Likewise the administration of benazepril does not substantially affect the pharmacokinetics of these medications (cimetidine kinetics were not studied).
The pharmacokinetics of benazeprilat, evaluated in pediatric patients with hypertension following oral administration of a single dose is presented in table below.
|Age group||C max (ng/mL)||T max * (h)||AUC 0-inf (ng/mL*h)||CL/F/wt (L/h/Kg)||T 1/2 (h)|
|> 1 to ≤ 24 months n=5||277 (192, 391)||1 (0.6, 2)||1328 (773, 2117)||0.26 (0.18, 0.4)||5 (4, 5.8)|
|> 2 to ≤ 6 years n=7||200 (168, 244)||2 (1.4, 2.4)||978 (842, 1152)||0.36 (0.31, 0.42)||5.5 (4.7, 6.5)|
|> 6 to ≤ 12 years n=7||221 (194, 258)||2 (1.2, 2.2)||1041 (855, 1313)||0.25 (0.21, 0.31)||5.5 (4.7, 6.5)|
|> 12 to ≤ 17 years n=8||287 (217, 420)||2 (1.3, 2.3)||1794 (1478, 2340)||0.16 (0.13, 0.21)||5.1 (4.2, 5.7)|
No evidence of carcinogenicity was found when benazepril was administered to rats and mice for up to two years at doses of up to 150 mg/kg/day. When compared on the basis of body weights, this dose is 110 times the maximum recommended human dose. When compared on the basis of body surface areas, this dose is 18 and 9 times (rats and mice, respectively) the maximum recommended human dose (calculations assume a patient weight of 60 kg). No mutagenic activity was detected in the Ames test in bacteria (with or without metabolic activation), in an in vitro test for forward mutations in cultured mammalian cells, or in a nucleus anomaly test. In doses of 50 to 500 mg/kg/day (6 to 60 times the maximum recommended human dose based on mg/m 2 comparison and 37 to 375 times the maximum recommended human dose based on a mg/kg comparison), benazepril had no adverse effect on the reproductive performance of male and female rats.
In single-dose studies, benazepril lowered blood pressure within 1 hour, with peak reductions achieved between 2 and 4 hours after dosing. The antihypertensive effect of a single dose persisted for 24 hours. In multiple-dose studies, once-daily doses of between 20 mg and 80 mg decreased seated pressure 24 hours after dosing by about 6 to 12 mm Hg systolic and 4 to 7 mm Hg diastolic. The trough values represent reductions of about 50% of that seen at peak.
Four dose-response studies using once-daily dosing were conducted in 470 mild-to-moderate hypertensive patients not using diuretics. The minimal effective once-daily dose of benazepril was 10 mg; but further falls in blood pressure, especially at morning trough, were seen with higher doses in the studied dosing range (10 to 80 mg). In studies comparing the same daily dose of benazepril given as a single morning dose or as a twice-daily dose, blood pressure reductions at the time of morning trough blood levels were greater with the divided regimen.
The antihypertensive effects of benazepril were not appreciably different in patients receiving high- or low-sodium diets.
In normal human volunteers, single doses of benazepril caused an increase in renal blood flow but had no effect on glomerular filtration rate.
Use of benazepril in combination with thiazide diuretics gives a blood-pressure-lowering effect greater than that seen with either agent alone. By blocking the renin-angiotensin-aldosterone axis, administration of benazepril tends to reduce the potassium loss associated with the diuretic.
In a clinical study of 107 pediatric patients, 7 to 16 years of age, with either systolic or diastolic pressure above the 95th percentile, patients were given 0.1 or 0.2 mg/kg then titrated up to 0.3 or 0.6 mg/kg with a maximum dose of 40 mg once daily. After four weeks of treatment, the 85 patients whose blood pressure was reduced on therapy were then randomized to either placebo or benazepril and were followed up for an additional two weeks. At the end of two weeks, blood pressure (both systolic and diastolic) in children withdrawn to placebo rose by 4 to 6 mm Hg more than in children on benazepril. No dose-response was observed.
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