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Mechanism of Action
Angiotensin II is formed from angiotensin I in a reaction catalyzed by angiotensin-converting enzymes (ACE, kinase II). Angiotensin II is the principal 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.
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 Edarbi to healthy subjects; no clinically significant effects on serum potassium or sodium were observed.
Effect on Cardiac Repolarization: A thorough QT/QTc study was conducted to assess the potential of azilsartan to prolong the QT/QTc interval in healthy subjects. There was no evidence of QT/QTc prolongation at a dose of 320 mg of Edarbi.
Azilsartan medoxomil is 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.
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.
Metabolism and Elimination
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 Edarbi. 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.
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 1 as change relative to reference (test/reference). Effects are modest and do not call for dosage adjustment.
Figure 1 : Impact of intrinsic factors on the
pharmacokinetics of azilsartan
Animal Toxicology and/or Pharmacology
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.
The antihypertensive effects of Edarbi have been demonstrated in a total of 7 double-blind, randomized studies, which included 5 placebo-controlled and 4 active comparator-controlled studies (not mutually exclusive). The studies ranged from 6 weeks to 6 months in duration, at doses ranging from 20 mg to 80 mg once daily. A total of 5941 patients (3672 given Edarbi, 801 given placebo, and 1468 given active comparator) with mild, moderate or severe hypertension were studied. Overall, 51% of patients were male and 26% were 65 years or older; 67% were white and 19% were black.
Two 6-week randomized, double blind studies compared the effect on blood pressure of Edarbi at doses of 40 mg and 80 mg, with placebo and with active comparators. Blood pressure reductions compared to placebo based on clinic blood pressure measurements at trough and 24 hour mean blood pressure by ambulatory blood pressure monitoring (ABPM) are shown in Table 1 for both studies. Edarbi, 80 mg, was statistically superior to placebo and active comparators for both clinic and 24 hour mean blood pressure measurements.
Table 1: Placebo Corrected Mean Change from Baseline in
Systolic / Diastolic Blood Pressure at 6 Weeks (mm Hg)
|Clinic Blood Pressure (Mean Baseline 157.4 / 92.5)||24 Hour Mean by ABPM (Mean Baseline 144.9 / 88.7)||Clinic Blood Pressure (Mean Baseline 159.0 / 91.8)||24 Hour Mean by ABPM (Mean Baseline 146.2 / 87.6)|
|Edarbi 40 mg||-14.6 / -6.2||-13.2 / -8.6||-12.4 / -7.1||-12.1 / -7.7|
|Edarbi 80 mg||-14.9 / -7.5||-14.3 / -9.4||-15.5 / -8.6||-13.2 / -7.9|
|Olmesartan 40 mg||-11.4 / -5.3||-11.7 / -7.7||-12.8 / -7.1||-11.2 / -7.0|
|Valsartan 320 mg||-9.5 / -4.4||-10.0 / -7.0|
In a study comparing Edarbi to valsartan over 24 weeks, similar results were observed. Most of the antihypertensive effect occurs within the first 2 weeks of dosing. Figure 2 shows the 24-hour ambulatory systolic and diastolic blood pressure profiles at endpoint.
Figure 2: Mean Ambulatory Blood
Pressure at 6 weeks by Dose and Hour
Other studies showed similar 24 hour ambulatory blood pressure profiles.
Edarbi has a sustained and consistent antihypertensive effect during long-term treatment, as shown in a study that randomized patients to placebo or continued Edarbi after 26 weeks. No rebound effect was observed following the abrupt cessation of Edarbi therapy. Edarbi was effective in reducing blood pressure regardless of the age, gender, or race of patients, but the effect, as monotherapy, was smaller, approximately half, in black patients, who tend to have low renin levels. This has been generally true for other angiotensin II antagonists and ACE inhibitors.
Edarbi has about its usual blood pressure lowering effect size when added to a calcium channel blocker (amlodipine) or a thiazide-type diuretic (chlorthalidone).
There are no trials of Edarbi demonstrating reductions in cardiovascular risk in patients with hypertension, but at least one pharmacologically similar drug has demonstrated such benefits.
Last reviewed on RxList: 10/16/2012
This monograph has been modified to include the generic and brand name in many instances.
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