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 Lotensin alone for up to 52 weeks had elevations of serum potassium
of up to 0.2 mEq/L. Similar patients treated with Lotensin 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 Lotensin remains to be elucidated.
While the mechanism through which benazepril lowers blood pressure is believed
to be primarily suppression of the renin-angiotensin-aldosterone system, benazepril
has an antihypertensive effect even in patients with low-renin hypertension
(see INDICATIONS).
Pharmacokinetics and Metabolism
Following oral administration of Lotensin, peak plasma concentrations of benazepril
are reached within 0.5-1.0 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 1-2 hours after drug intake in the fasting state and 2-4 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 0.24-23.6 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
Lotensin 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 10-80 mg.
In adults, the effective half-life of accumulation of benazeprilat
following multiple dosing of benazepril hydrochloride is 10-11 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%-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.
In pediatric patients, (N=45) hypertensive, age 6 to 16 years,
given multiple daily doses of Lotensin (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 Lotensin cause inhibition of plasma ACE activity by at least 80%-90% for at least 24 hours after dosing. Pressor responses to exogenous angiotensin I were inhibited by 60%-90% (up to 4 hours post-dose) at the 10-mg dose.
Hypertension
Adult
Administration of Lotensin 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, Lotensin lowered blood pressure within 1 hour, with
peak reductions achieved 2-4 hours after dosing. The antihypertensive effect
of a single dose persisted for 24 hours. In multiple-dose studies, once-daily
doses of 20-80 mg decreased seated pressure (systolic/diastolic) 24 hours after
dosing by about 6 -12 /4-7 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 Lotensin was 10 mg; but further falls in blood pressure, especially
at morning trough, were seen with higher doses in the studied dosing range (10-80
mg). In studies comparing the same daily dose of Lotensin 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 1-2 weeks. The antihypertensive effects of Lotensin
have continued during therapy for at least two years. Abrupt withdrawal of Lotensin
has not been associated with a rapid increase in blood pressure.
In patients with mild-to-moderate hypertension, Lotensin 10-20 mg was similar
in effectiveness to captopril, hydrochlorothiazide, nifedipine SR, and propranolol.
The antihypertensive effects of Lotensin 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.
Use of Lotensin 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 Lotensin tends to reduce the potassium loss associated
with the diuretic.
Pediatric
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 mmHg more than in children on benazepril. No dose-response was observed for the three doses.
Last updated on RxList: 8/27/2008