Benazepril Hydrochloride

BENAZEPRIL HYDROCHLORIDE — benazepril hydrochloride tablet, film coated
Greenstone LLC

USE IN PREGNANCY

When used in pregnancy, ACE inhibitors can cause injury and even death to the developing fetus. When pregnancy is detected, benazepril should be discontinued as soon as possible. See WARNINGS, Fetal/Neonatal Morbidity and Mortality.

DESCRIPTION

Benazepril hydrochloride is a white to off-white crystalline powder, soluble (>100 mg/mL) in water, in ethanol, and in methanol. Its chemical name is 3-[[1-(ethoxy-carbonyl)-3-phenyl-(1S)-propyl]amino]-2,3,4,5-tetrahydro-2-oxo-1H -1-(3S)-benzazepine-1-acetic acid monohydrochloride; its structural formula is

Benazepril Chemical Structure
(click image for full-size original)

Its molecular formula is C24 H28 N2 O5 •HCl, and its molecular weight is 460.96.

Benazeprilat, the active metabolite of benazepril, is a non-sulfhydryl angiotensin-converting enzyme inhibitor. Benazepril is converted to benazeprilat by hepatic cleavage of the ester group.

Benazepril hydrochloride is supplied as tablets containing 10 mg, 20 mg, and 40 mg of benazepril hydrochloride for oral administration. The inactive ingredients are microcrystalline cellulose, lactose monohydrate, pregelatinised starch, crospovidone, colloidal silicon dioxide, magnesium stearate, hypromellose, titanium dioxide, polyethylene glycol 400, polysorbate 80, iron oxide yellow (10 mg) and iron oxide red (20 mg and 40 mg).

CLINICAL PHARMACOLOGY

Mechanism of Action

Benazepril and benazeprilat inhibit angiotensin-converting enzyme (ACE) in human subjects and animals. ACE is a peptidyl dipeptidase that catalyzes the conversion of angiotensin I to the vasoconstrictor substance, angiotensin II. Angiotensin II also stimulates aldosterone secretion by the adrenal cortex.

Inhibition of ACE results in decreased plasma angiotensin II, which leads to decreased vasopressor activity and to decreased aldosterone secretion. The latter decrease may result in a small increase of serum potassium. Hypertensive patients treated with benazepril alone for up to 52 weeks had elevations of serum potassium of up to 0.2 mEq/L. Similar patients treated with benazepril and hydrochlorothiazide for up to 24 weeks had no consistent changes in their serum potassium (see PRECAUTIONS).

Removal of angiotensin II negative feedback on renin secretion leads to increased plasma renin activity. In animal studies, benazepril had no inhibitory effect on the vasopressor response to angiotensin II and did not interfere with the hemodynamic effects of the autonomic neurotransmitters acetylcholine, epinephrine, and norepinephrine.

ACE is identical to kininase, an enzyme that degrades bradykinin. Whether increased levels of bradykinin, a potent vasodepressor peptide, play a role in the therapeutic effects of benazepril remains to be elucidated.

INDICATIONS AND USAGE).

Pharmacokinetics and Metabolism

Following oral administration of benazepril, peak plasma concentrations of benazepril are reached within 0.5 to 1 hours. The extent of absorption is at least 37% as determined by urinary recovery and is not significantly influenced by the presence of food in the GI tract.

Cleavage of the ester group (primarily in the liver) converts benazepril to its active metabolite, benazeprilat. Peak plasma concentrations of benazeprilat are reached 1 to 2 hours after drug intake in the fasting state and 2 to 4 hours after drug intake in the nonfasting state. 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, which has much greater ACE inhibitory activity than benazepril, and to the glucuronide conjugates of benazepril and benazeprilat. Only trace amounts of an administered dose of benazepril can be recovered in the urine as unchanged benazepril, while about 20% of the dose is excreted as benazeprilat, 4% as benazepril glucuronide, and 8% as benazeprilat glucuronide.

The kinetics of benazepril are approximately dose-proportional within the dosage range of 10 to 80 mg.

In adults, the effective half-life of accumulation of benazeprilat following multiple dosing 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.

The kinetics did not change, and there was no significant accumulation during chronic administration (28 days) of once-daily doses between 5 mg and 20 mg. Accumulation ratios based on AUC and urinary recovery of benazeprilat were 1.19 and 1.27, respectively.

Benazepril and benazeprilat are cleared predominantly by renal excretion in healthy subjects with normal renal function. Nonrenal (i.e., biliary) excretion accounts for approximately 11% to 12% of benazeprilat excretion in healthy subjects. In patients with renal failure, biliary clearance may compensate to an extent for deficient renal clearance.

In patients with renal insufficiency, the disposition of 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).

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 and benazeprilat do not appear to be influenced by age.

(N=45) hypertensive, age 6 to 16 years, given multiple daily doses of benazepril (0.1 to 0.5 mg/kg), the clearance of benazeprilat for children 6 to 12 years old was 0.35 L/hr/kg, more than twice that of healthy adults receiving a single dose of 10 mg (0.13 L/hr/kg). In adolescents, it was 0.17 L/hr/kg, 27% higher than that of healthy adults. The terminal elimination half-life of benazeprilat in pediatric patients was around 5 hours, one-third that observed in adults.

Pharmacodynamics

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.

Hypertension

Adult

Administration of benazepril to patients with mild-to-moderate hypertension results in a reduction of both supine and standing blood pressure to about the same extent with no compensatory tachycardia. Symptomatic postural hypotension is infrequent, although it can occur in patients who are salt- and/or volume-depleted (see WARNINGS).

In single-dose studies, benazepril lowered blood pressure within 1 hour, with peak reductions achieved 2 to 4 hours after dosing. The antihypertensive effect of a single dose persisted for 24 hours. In multiple-dose studies, once-daily doses of 20 to 80 mg decreased seated pressure (systolic/diastolic) 24 hours after dosing by about 6 to 12/4 to 7 mmHg. 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.

During chronic therapy, the maximum reduction in blood pressure with any dose is generally achieved after 1 to 2 weeks. The antihypertensive effects of benazepril have continued during therapy for at least two years. Abrupt withdrawal of benazepril has not been associated with a rapid increase in blood pressure.

In patients with mild-to-moderate hypertension, benazepril 10 to 20 mg was similar in effectiveness to captopril, hydrochlorothiazide, nifedipine SR, and propranolol.

The antihypertensive effects of benazepril were not appreciably different in patients receiving high- or low-sodium diets.

In hemodynamic studies in dogs, blood pressure reduction was accompanied by a reduction in peripheral arterial resistance, with an increase in cardiac output and renal blood flow and little or no change in heart rate. In normal human volunteers, single doses of benazepril caused an increase in renal blood flow but had no effect on glomerular filtration rate.

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