Amlodipine Besylate and Benazepril Hydrochloride (Page 5 of 7)

12.3 Pharmacokinetics

The rate and extent of absorption of benazepril and amlodipine from amlodipine besylate and benazepril hydrochloride capsules are not significantly different, respectively, from the rate and extent of absorption of benazepril and amlodipine from individual tablet formulations. Absorption from the individual tablets is not influenced by the presence of food in the gastrointestinal tract; food effects on absorption from amlodipine besylate and benazepril hydrochloride capsules have not been studied.

Following oral administration of amlodipine besylate and benazepril hydrochloride capsules, peak plasma concentrations of benazepril are reached in 0.5-2 hours. Cleavage of the ester group (primarily in the liver) converts benazepril to its active metabolite, benazeprilat, which reaches peak plasma concentrations in 1.5-4 hours. The extent of absorption of benazepril is at least 37%.

Peak plasma concentrations of amlodipine are reached 6-12 hours after administration of amlodipine besylate and benazepril hydrochloride capsules; the extent of absorption is 64%-90%.

The apparent volumes of distribution of amlodipine and benazeprilat are about 21 L/kg and 0.7 L/kg, respectively. Approximately 93% of circulating amlodipine is bound to plasma proteins, and the bound fraction of benazeprilat is slightly higher. On the basis of in vitro studies, benazeprilat’s degree of protein binding should be unaffected by age, by hepatic dysfunction, or—over the therapeutic concentration range—by concentration.

Benazeprilat has much greater ACE-inhibitory activity than benazepril, and the metabolism of benazepril to benazeprilat is almost complete. Only trace amounts of an administered dose of benazepril can be recovered unchanged in the urine; about 20% of the dose is excreted as benazeprilat, 8% as benazeprilat glucuronide, and 4% as benazepril glucuronide.

Amlodipine is extensively metabolized in the liver, with 10% of the parent compound and 60% of the metabolites excreted in the urine. In patients with hepatic dysfunction, decreased clearance of amlodipine may increase the area-under-the-plasma-concentration curve by 40%-60%, and dosage reduction may be required [see Dosage and Administratio n (2)]. In patients with renal impairment, the pharmacokinetics of amlodipine are essentially unaffected.

Benazeprilat’s effective elimination half-life is 10-11 hours, while that of amlodipine is about 2 days, so steady-state levels of the two components are achieved after about a week of once-daily dosing. The clearance of benazeprilat from the plasma is primarily renal, but biliary excretion accounts for 11%-12% of benazepril elimination in normal subjects. In patients with severe renal insufficiency (creatinine clearance less than 30 mL/min), peak benazeprilat levels and the time to steady state may be increased [see Dosage and Administratio n (2)]. In patients with hepatic impairment, on the other hand, the pharmacokinetics of benazeprilat are essentially unaffected.

Although the pharmacokinetics of benazepril and benazeprilat are unaffected by age, clearance of amlodipine is decreased in the elderly, with resulting increases of 35%-70% in peak plasma levels, elimination half-life, and area-under-the-plasma-concentration curve. Dose adjustment may be required.

13 NONCLINICAL TOXICOLOGY

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Carcinogenicity and mutagenicity studies have not been conducted with this combination. However, these studies have been conducted with amlodipine and benazepril alone (see below). No adverse effects on fertility occurred when the benazepril:amlodipine combination was given orally to rats of either sex at doses up to 15:7.5 mg (benazepril:amlodipine)/kg/day, prior to mating and throughout gestation.

Benazepril

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 surface area, 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, in an in vitro test for forward mutations in cultured mammalian cells, or in a nucleus anomaly test. At doses of 50-500 mg/kg/day (6-60 times the maximum recommended human dose on a body surface area basis), benazepril had no adverse effect on the reproductive performance of male and female rats.

Amlodipine

Rats and mice treated with amlodipine maleate in the diet for up to two years, at concentrations calculated to provide daily dosage levels of 0.5, 1.25, and 2.5 mg amlodipine/kg/day, showed no evidence of a carcinogenic effect of the drug. For the mouse, the highest dose was, on a body surface area basis, similar to the maximum recommended human dose [MRHD] of 10 mg amlodipine/day. For the rat, the highest dose was, on a body surface area basis, about two and a half times the MRHD. (Calculations based on a 60 kg patient.) Mutagenicity studies conducted with amlodipine maleate revealed no drug-related effects at either the gene or chromosome level. There was no effect on the fertility of rats treated orally with amlodipine maleate (males for 64 days and females for 14 days prior to mating) at doses of up to 10 mg amlodipine/kg/day (about 10 times the MRHD of 10 mg/day on a body surface area basis).

13.3 Reproductive Toxicity

When rats received benazepril:amlodipine at doses ranging from 5:2.5 to 50:25 mg/kg/day, dystocia was observed at an increasing dose-related incidence at all doses tested. On a body surface area basis, the 2.5 mg/kg/day dose of amlodipine is 3.6 times the amlodipine dose delivered when the maximum recommended dose of amlodipine besylate and benazepril hydrochloride is given to a 50-kg woman. Similarly, the 5 mg/kg/day dose of benazepril is approximately twice the benazepril dose delivered when the maximum recommended dose of amlodipine besylate and benazepril hydrochloride is given to a 50-kg woman. No teratogenic effects were seen when benazepril and amlodipine were administered in combination to pregnant rats or rabbits. Rats received doses of up to 50:25 mg (benazepril:amlodipine)/kg/day (24 times the maximum recommended human dose on a body surface area basis, assuming a 50-kg woman). Rabbits received doses of up to 1.5:0.75 mg/kg/day (equivalent to the maximum recommended dose of amlodipine besylate and benazepril hydrochloride given to a 50-kg woman).

Benazepril

No teratogenic effects of benazepril were seen in studies of pregnant rats, mice, and rabbits. On a body surface area basis, the maximum doses used in these studies were 60 times (in rats), 9 times (in mice), and about equivalent to (in rabbits) the maximum recommended human dose (assuming a 50-kg woman).

Amlodipine

No evidence of teratogenicity or other embryo/fetal toxicity was found when pregnant rats and rabbits were treated orally with amlodipine maleate at doses of up to 10 mg amlodipine/kg/day (respectively, about 10 and 20 times the maximum recommended human dose [MRHD] of 10 mg amlodipine on a body surface area basis) during their respective periods of major organogenesis. (Calculations based on a patient weight of 60 kg.) However, litter size was significantly decreased (by about 50%) and the number of intrauterine deaths was significantly increased (about 5-fold) for rats receiving amlodipine maleate at a dose equivalent to 10 mg amlodipine/kg/day for 14 days before mating and throughout mating and gestation. Amlodipine maleate has been shown to prolong both the gestation period and the duration of labor in rats at this dose. There are no adequate and well-controlled studies in pregnant women. Amlodipine should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

14 CLINICAL STUDIES

Over 950 patients received amlodipine besylate and benazepril hydrochloride once daily in six double-blind, placebo-controlled studies. The antihypertensive effect of a single dose persisted for 24 hours, with peak reductions achieved 2-8 hours after dosing.

Once-daily doses of benazepril/amlodipine using benazepril doses of 10-20 mg and amlodipine doses of 2.5-10 mg decreased seated pressure (systolic/diastolic) 24 hours after dosing by about 10-25/6-13 mmHg.

In two studies in patients not adequately controlled on either benazepril 40 mg alone (n=329) or amlodipine 10 mg alone (n=812) once daily doses of amlodipine besylate and benazepril hydrochloride 10/40 mg further decreased seated blood pressure compared to the respective monotherapy alone.

Combination therapy was effective in blacks and nonblacks. Both components contributed to the antihypertensive efficacy in nonblacks, but virtually all of the antihypertensive effect in blacks could be attributed to the amlodipine component. Among nonblack patients in placebo-controlled trials comparing amlodipine besylate and benazepril hydrochloride to the individual components, the blood pressure lowering effects of the combination were shown to be additive and in some cases synergistic.

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