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Mechanism Of Action
The active ingredients of Edarbyclor target two separate mechanisms involved in blood pressure regulation. Azilsartan blocks the vasoconstriction and sodium retaining effects of angiotensin II on cardiac, vascular smooth muscle, adrenal and renal cells. Chlorthalidone produces diuresis with increased excretion of sodium and chloride at the cortical diluting segment of the ascending limb of Henle's loop of the nephron.
Angiotensin II is formed from angiotensin I in a reaction catalyzed by angiotensin-converting enzymes (ACE, kinase II). Angiotensin II is the principle pressor agent of the renin-angiotensin system, with effects that include vasoconstriction, stimulation of synthesis and release of aldosterone, cardiac stimulation, and renal reabsorption of sodium. Azilsartan blocks the vasoconstrictor and aldosteronesecreting effects of angiotensin II by selectively blocking the binding of angiotensin II to the AT1 receptor in many tissues, such as vascular smooth muscle and the adrenal gland. Its action is, therefore, independent of the pathway for angiotensin II synthesis.
An AT2 receptor is also found in many tissues, but this receptor is not known to be associated with cardiovascular homeostasis. Azilsartan has more than a 10,000-fold greater affinity for the AT1 receptor than for the AT2 receptor.
Blockade of the renin-angiotensin system with ACE inhibitors, which inhibit the biosynthesis of angiotensin II from angiotensin I, is widely used in the treatment of hypertension. ACE inhibitors also inhibit the degradation of bradykinin, a reaction catalyzed by ACE. Because azilsartan does not inhibit ACE (kinase II), it should not affect bradykinin levels. Whether this difference has clinical relevance is not yet known. Azilsartan does not bind to or block other receptors or ion channels known to be important in cardiovascular regulation.
Blockade of the angiotensin II receptor inhibits the negative regulatory feedback of angiotensin II on renin secretion, but the resulting increased plasma renin activity and angiotensin II circulating levels do not overcome the effect of azilsartan on blood pressure.
Chlorthalidone produces diuresis with increased excretion of sodium and chloride. The site of action appears to be the cortical diluting segment of the ascending limb of Henle's loop of the nephron. The diuretic effects of chlorthalildone lead to decreased extracellular fluid volume, plasma volume, cardiac output, total exchangeable sodium, glomerular filtration rate, and renal plasma flow. Although the mechanism of action of chlorthalidone and related drugs is not wholly clear, sodium and water depletion appear to provide a basis for its antihypertensive effect.
Edarbyclor tablets have been shown to be effective in lowering blood pressure. Both azilsartan medoxomil and chlorthalidone lower blood pressure by reducing peripheral resistance but through complementary mechanisms.
Azilsartan inhibits the pressor effects of an angiotensin II infusion in a dose-related manner. An azilsartan single dose equivalent to 32 mg azilsartan medoxomil inhibited the maximal pressor effect by approximately 90% at peak, and approximately 60% at 24 hours. Plasma angiotensin I and II concentrations and plasma renin activity increased while plasma aldosterone concentrations decreased after single and repeated administration of azilsartan medoxomil to healthy subjects; no clinically significant effects on serum potassium or sodium were observed.
The diuretic effect of chlorthalidone occurs in approximately 2.6 hours and continues for up to 72 hours.
Following oral administration of Edarbyclor, peak plasma concentrations of azilsartan and chlorthalidone are reached at 3 and 1 hours, respectively. The rate (Cmax and Tmax) and extent (AUC) of absorption of azilsartan are similar when it is administered alone or with chlorthalidone. The extent (AUC) of absorption of chlorthalidone is similar when it is administered alone or with azilsartan medoxomil; however, the Cmax of chlorthalidone from Edarbyclor was 47% higher. The elimination half-lives of azilsartan and chlorthalidone are approximately 12 hours and 45 hours, respectively.
There is no clinically significant effect of food on the bioavailability of Edarbyclor.
Azilsartan medoxomil is rapidly hydrolyzed to azilsartan, the active metabolite, in the gastrointestinal tract during absorption. Azilsartan medoxomil is not detected in plasma after oral administration. Dose proportionality in exposure was established for azilsartan in the azilsartan medoxomil dose range of 20 mg to 320 mg after single or multiple dosing.
The estimated absolute bioavailability of azilsartan following administration of azilsartan medoxomil is approximately 60%. After oral administration of azilsartan medoxomil, peak plasma concentrations (Cmax) of azilsartan are reached within 1.5 to 3 hours. Food does not affect the bioavailability of azilsartan.
Azilsartan medoxomil: The volume of distribution of azilsartan is approximately 16L. Azilsartan is highly bound to human plasma proteins ( > 99%), mainly serum albumin. Protein binding is constant at azilsartan plasma concentrations well above the range achieved with recommended doses.
In rats, minimal azilsartan-associated radioactivity crossed the blood-brain barrier. Azilsartan passed across the placental barrier in pregnant rats and was distributed to the fetus. Chlorthalidone: In whole blood, chlorthalidone is predominantly bound to erythrocyte carbonic anhydrase. In the plasma, approximately 75% of chlorthalidone is bound to plasma proteins, 58% of the drug being bound to albumin.
Metabolism and Elimination
Azilsartan medoxomil: Azilsartan is metabolized to two primary metabolites. The major metabolite in plasma is formed by O-dealkylation, referred to as metabolite M-II, and the minor metabolite is formed by decarboxylation, referred to as metabolite M-I. Systemic exposures to the major and minor metabolites in humans were approximately 50% and less than 1% of azilsartan, respectively. M-I and MII do not contribute to the pharmacologic activity of azilsartan medoxomil. The major enzyme responsible for azilsartan metabolism is CYP2C9.
Following an oral dose of 14C-labeled azilsartan medoxomil, approximately 55% of radioactivity was recovered in feces and approximately 42% in urine, with 15% of the dose excreted in urine as azilsartan. The elimination half-life of azilsartan is approximately 11 hours and renal clearance is approximately 2.3 mL/min. Steady-state levels of azilsartan are achieved within 5 days and no accumulation in plasma occurs with repeated once-daily dosing.
Chlorthalidone: The major portion of the drug is excreted unchanged by the kidneys. Nonrenal routes of elimination have yet to be clarified. Data are not available regarding percentage of dose as unchanged drug and metabolites, concentration of the drug in body fluids, degree of uptake by a particular organ or in the fetus, or passage across the blood-brain barrier.
Azilsartan medoxomil: The effect of demographic and functional factors on the pharmacokinetics of azilsartan was studied in single and multiple dose studies. Pharmacokinetic measures indicating the magnitude of the effect on azilsartan are presented in Figure 2 as change relative to reference (test/reference).
Figure 2: Impact of intrinsic factors on the
pharmacokinetics of azilsartan
Animal Toxicology And/Or Pharmacology
The safety profiles of azilsartan medoxomil and chlorthalidone monotherapy have been individually established. To characterize the toxicological profile for Edarbyclor, a 13-week repeat-dose toxicity study was conducted in rats. The results of this study indicated that the combined administration of azilsartan medoxomil, M-II, and chlorthalidone resulted in increased exposures to chlorthalidone. Pharmacologically-mediated toxicity, including suppression of body weight gain and decreased food consumption in male rats, and increases in blood urea nitrogen in both sexes, was enhanced by coadministration of azilsartan medoxomil, M-II, and chlorthalidone. With the exception of these findings, there were no toxicologically synergistic effects in this study.
In an embryo-fetal developmental study in rats, there was no teratogenicity or increase in fetal mortality in the litters of dams receiving azilsartan medoxomil, M-II and chlorthalidone concomitantly at maternally toxic doses.
In peri-and postnatal rat development studies, adverse effects on pup viability, delayed incisor eruption and dilatation of the renal pelvis along with hydronephrosis were seen when azilsartan medoxomil was administered to pregnant and nursing rats at 1.2 times the MRHD on a mg/m² basis. Reproductive toxicity studies indicated that azilsartan medoxomil was not teratogenic when administered at oral doses up to 1000 mg azilsartan medoxomil/kg/day to pregnant rats (122 times the MRHD on a mg/m² basis) or up to 50 mg azilsartan medoxomil/kg/day to pregnant rabbits (12 times the MRHD on a mg/m² basis). M-II also was not teratogenic in rats or rabbits at doses up to 3000 mg MII/kg/day. Azilsartan crossed the placenta and was found in the fetuses of pregnant rats and was excreted into the milk of lactating rats.
Reproduction studies have been performed in the rat and the rabbit at doses up to 420 times the human dose and have revealed no evidence of harm to the fetus. Thiazides cross the placental barrier and appear in cord blood.
Biochemical studies in animals have suggested reasons for the prolonged effect of chlorthalidone. Absorption from the gastrointestinal tract is slow because of its low solubility. After passage to the liver, some of the drug enters the general circulation, while some is excreted in the bile, to be reabsorbed later. In the general circulation, it is distributed widely to the tissue, but is taken up in highest concentrations by the kidneys, where amounts have been found 72 hours after ingestion, long after it has disappeared from other tissues. The drug is excreted unchanged in the urine.
The antihypertensive effects of Edarbyclor have been demonstrated in a total of 5 randomized controlled studies, which included 4 double-blind, active-controlled studies and 1 open-label, long-term active-controlled study. The studies ranged from 8 weeks to 12 months in duration, at doses ranging from 20/12.5 mg to 80/25 mg once daily. A total of 5310 patients (3082 given Edarbyclor and 2228 given active comparator) with moderate or severe hypertension were studied. Overall, randomized patients had a mean age of 57 years, and included 52% males, 72% whites, 21% blacks, 15% with diabetes, 70% with mild or moderate renal impairment, and a mean BMI of 31.6 kg/m² .
An 8-week, multicenter, randomized, double-blind, active-controlled, parallel group factorial trial in patients with moderate to severe hypertension compared the effect on blood pressure of Edarbyclor with the respective monotherapies. The trial randomized 1714 patients with baseline systolic blood pressure between 160 and 190 mm Hg (mean 165 mm Hg) and a baseline diastolic blood pressure < 119 mm Hg (mean 95 mm Hg) to one of the 11 active treatment arms.
The 6 treatment combinations of azilsartan medoxomil 20, 40, or 80 mg and chlorthalidone 12.5 or 25 mg resulted in statistically significant reduction in systolic and diastolic blood pressure as determined by ambulatory blood pressure monitoring (ABPM) (Table 2) and clinic measurement (Table 3) at trough compared with the respective individual monotherapies. The clinic blood pressure reductions appear larger than those observed with ABPM, because the former include a placebo effect, which was not directly measured. Most of the antihypertensive effect of Edarbyclor occurs within 1-2 weeks of dosing. The blood pressure lowering effect was maintained throughout the 24-hour period (Figure 3).
Table 2: Mean Change from Baseline in
Systolic/Diastolic Blood Pressure (mm Hg) as Measured by ABPM at Trough (22-24
Hours Post-Dose) at Week 8: Combination Therapy vs Monotherapy
|Chlorthalidone, mg||Azilsartan Medoxomil, mg|
|0||N/A||-12 / -8||-13 / -7||-15 / -9|
|12.5||-13 / -7||-23 / -13||-24 / -14||-26 / -17|
|25||-16 / -8||-26 / -15||-30 / -17||-28 / -16|
Table 3: Mean Change from
Baseline in Clinic Systolic/Diastolic Blood Pressure (mm Hg) at Week 8:
Combination Therapy vs Monotherapy
|Chlorthalidone, mg||Azilsartan Medoxomil, mg|
|0||N/A||-20 / -7||-23 / -9||-24 / -10|
|12.5||-21 / -7||-34 / -14||-37 / -16||-37 / -17|
|25||-27 / -9||-37 / -16||-40 / -17||-40 / -19|
Figure 3:Mean Change from
Baseline at Week 8 in Ambulatory Systolic Blood Pressure (mm Hg) by Treatment
Edarbyclor was effective in reducing blood pressure regardless of age, gender, or race.
Edarbyclor was effective in treating black patients (usually a low-renin population).
In a 12-week, double-blind forced-titration trial, Edarbyclor 40/25 mg was statistically superior (P < 0.001) to olmesartan medoxomil – hydrochlorothiazide (OLM/HCTZ) 40/25 mg in reducing systolic blood pressure in patients with moderate to severe hypertension (Table 4). Similar results were observed in all subgroups, including age, gender, or race of patients.
Table 4: Mean Change in
Systolic/Diastolic Blood Pressure (mm Hg) at Week 12
|Edarbyclor 40/25 mg
|OLM/HCTZ 40/25 mg
|Clinic (Mean Baseline 165/96 mm Hg)||-43 / -19||-37 / -16|
|Trough by ABPM (22-24 hours) (Mean Baseline 153/92 mm Hg)||-33 / -20||-26 / -16|
Edarbyclor lowered blood pressure more effectively than OLM/HCTZ at each hour of the 24-hour interdosing period as measured by ABPM.
There are no trials of Edarbyclor demonstrating reductions in cardiovascular risk in patients with hypertension; however, trials with chlorthalidone and at least one drug pharmacologically similar to azilsartan medoxomil have demonstrated such benefits.
Last reviewed on RxList: 8/4/2014
This monograph has been modified to include the generic and brand name in many instances.
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