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Mechanism of Action
The effects of combined treatment of aliskiren, amlodipine and HCTZ arise from the actions of these three agents on different but complementary mechanisms that regulate blood pressure. Together, inhibition of the renin-angiotensinaldosterone system (RAAS), inhibition of calcium channel-mediated vasoconstriction, and increase of sodium chloride excretion lowers blood pressure to a greater degree than the individual components.
Renin is secreted by the kidney in response to decreases in blood volume and renal perfusion. Renin cleaves angiotensinogen to form the inactive decapeptide angiotensin I (Ang I). Ang I is converted to the active octapeptide angiotensin II (Ang II) by angiotensin-converting enzyme (ACE) and non-ACE pathways. Ang II is a powerful vasoconstrictor and leads to the release of catecholamines from the adrenal medulla and prejunctional nerve endings. It also promotes aldosterone secretion and sodium reabsorption. Together, these effects increase blood pressure. Ang II also inhibits renin release, thus providing a negative feedback to the system. This cycle, from renin through angiotensin to aldosterone and its associated negative feedback loop, is known as the renin-angiotensin-aldosterone system (RAAS). Aliskiren is a direct renin inhibitor, decreasing plasma renin activity (PRA) and inhibiting the conversion of angiotensinogen to Ang I. Whether aliskiren affects other RAAS components, e.g., ACE or non-ACE pathways, is not known.
All agents that inhibit the RAAS, including renin inhibitors, suppress the negative feedback loop, leading to a compensatory rise in plasma renin concentration. When this rise occurs during treatment with ACE inhibitors and ARBs, the result is increased levels of PRA. During treatment with aliskiren, however, the effect of increased renin levels is blocked, so that PRA, Ang I and Ang II are all reduced, whether aliskiren is used as monotherapy or in combination with other antihypertensive agents.
Amlodipine is a dihydropyridine calcium channel blocker that inhibits the transmembrane influx of calcium ions into vascular smooth muscle and cardiac muscle. Experimental data suggest that amlodipine binds to both dihydropyridine and nondihydropyridine binding sites. The contractile processes of cardiac muscle and vascular smooth muscle are dependent upon the movement of extracellular calcium ions into these cells through specific ion channels. Amlodipine inhibits calcium ion influx across cell membranes selectively, with a greater effect on vascular smooth muscle cells than on cardiac muscle cells. Negative inotropic effects can be detected in vitro but such effects have not been seen in intact animals at therapeutic doses. Serum calcium concentration is not affected by amlodipine. Within the physiologic pH range, amlodipine is an ionized compound (pKa=8.6), and its kinetic interaction with the calcium channel receptor is characterized by a gradual rate of association and dissociation with the receptor binding site, resulting in a gradual onset of effect.
The mechanism of action of the antihypertensive effect of thiazides is unknown.
HCTZ is a thiazide diuretic. Thiazides affect the renal tubular mechanisms of electrolyte reabsorption, directly increasing excretion of sodium and chloride in approximately equivalent amounts. Indirectly, the diuretic action of HCTZ reduces plasma volume, with consequent increases in plasma renin activity, increases in aldosterone secretion, increases in urinary potassium loss, and decreases in serum potassium. The renin-aldosterone link is mediated by angiotensin II, so coadministration of agents that block the production or function of angiotensin II tends to reverse the potassium loss associated with these diuretics.
PRA reductions in clinical trials ranged from approximately 50% to 80%, were not dose-related and did not correlate with blood pressure reductions. The clinical implications of the differences in effect on PRA are not known.
Following administration of therapeutic doses to patients with hypertension, amlodipine produces vasodilation resulting in a reduction of supine and standing blood pressures. These decreases in blood pressure are not accompanied by a significant change in heart rate or plasma catecholamine levels with chronic dosing. Although the acute intravenous administration of amlodipine decreases arterial blood pressure and increases heart rate in hemodynamic studies of patients with chronic stable angina, chronic oral administration of amlodipine in clinical trials did not lead to clinically significant changes in heart rate or blood pressures in normotensive patients with angina.
With chronic once-daily administration, antihypertensive effectiveness is maintained for at least 24 hours. Plasma concentrations correlate with effect in both young and elderly patients. The magnitude of reduction in blood pressure with amlodipine is also correlated with the height of pretreatment elevation; thus, individuals with moderate hypertension (diastolic pressure 105-114 mmHg) had about 50% greater response than patients with mild hypertension (diastolic pressure 90-104 mmHg). Normotensive subjects experienced no clinically significant change in blood pressure (+1/-2 mmHg).
In hypertensive patients with normal renal function, therapeutic doses of amlodipine resulted in a decrease in renal vascular resistance and an increase in glomerular filtration rate and effective renal plasma flow without change in filtration fraction or proteinuria.
As with other calcium channel blockers, hemodynamic measurements of cardiac function at rest and during exercise (or pacing) in patients with normal ventricular function treated with amlodipine have generally demonstrated a small increase in cardiac index without significant influence on dP/dt or on left ventricular end diastolic pressure or volume. In hemodynamic studies, amlodipine has not been associated with a negative inotropic effect when administered in therapeutic dose range to intact animals and man, even when co-administered with beta-blockers to man. Similar findings, however, have been observed in normal or well-compensated patients with heart failure with agents possessing significant negative inotropic effects.
Amlodipine does not change sinoatrial nodal function or atrioventricular conduction in intact animals or man. In patients with chronic stable angina, intravenous administration of 10 mg did not significantly alter A-H and H-V conduction and sinus node recovery time after pacing. Similar results were obtained in patients receiving amlodipine and concomitant beta-blockers. In clinical studies in which amlodipine was administered in combination with beta-blockers to patients with either hypertension or angina, no adverse effects of electrocardiographic parameters were observed. In clinical trials with angina patients alone, amlodipine therapy did not alter electrocardiographic intervals or produce higher degrees of AV blocks.
Amlodipine has indications other than hypertension, which can be found in the Norvasc® package insert.
After oral administration of HCTZ, diuresis begins within 2 hours, peaks in about 4 hours, and lasts about 6 to 12 hours.
In an active-controlled trial which established the clinical efficacy of Amturnide in hypertensive patients, Amturnide was associated with a 34% reduction in PRA compared to a 63% reduction with aliskiren/amlodipine, 64% reduction with aliskiren/HCTZ and a 170% elevation with amlodipine/HCTZ.
Absorption and Distribution
Following oral administration of the fixed combination of aliskiren, amlodipine, and HCTZ, peak concentrations were achieved within 1-2 hours, 6-12 hours, and 1-4 hours for aliskiren, amlodipine and HCTZ, respectively. The rate and extent of absorption of aliskiren, amlodipine, and HCTZ following administration of the fixed combination are similar to when they are administered as individual dosage forms.
When Amturnide is taken with food, mean AUC and Cmax of aliskiren are decreased by 78% and 89%, respectively. There is no impact of food on the exposures of amlodipine and HCTZ.
Aliskiren is poorly absorbed (bioavailability about 2.5%) with an accumulation half life of about 24 hours. Steady state blood levels are reached in about 7-8 days. Following oral administration, peak plasma concentrations of aliskiren are reached within 1-3 hours. When taken with a high fat meal, mean AUC and Cmax of aliskiren are decreased by 71% and 85% respectively. In the clinical trials, aliskiren was administered without a fixed relation to meals.
Peak plasma concentrations of amlodipine are reached 6-12 hours after an oral administration of amlodipine. Absolute bioavailability has been estimated to be between 64% and 90%. The bioavailability of amlodipine is not altered by the presence of food. Steady state plasma levels of amlodipine are reached after 7 to 8 days of consecutive daily dosing. Approximately 93% of circulating amlodipine is bound to plasma proteins in hypertensive patients.
Metabolism and Elimination
About one-fourth of the absorbed dose appears in the urine as parent drug. How much of the absorbed dose is metabolized is unknown. Based on the in vitro studies, the major enzyme responsible for aliskiren metabolism appears to be CYP 3A4. Aliskiren does not inhibit the CYP450 isoenzymes (CYP 1A2, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A) or induce CYP 3A4.
Transporters: Pgp (MDR1/Mdr1a/1b) was found to be the major efflux system involved in absorption and disposition of aliskiren in preclinical studies. The potential for drug interactions at the Pgp site will likely depend on the degree of inhibition of this transporter.
The effect of co-administered drugs on the pharmacokinetics of aliskiren and vice versa, were studied in several single and multiple dose studies. Pharmacokinetic measures indicating the magnitude of these interactions are presented in Figure 1 (impact of co-administered drugs on aliskiren) and Figure 2 (impact on co-administered drugs).
Figure 1: The impact of co-administered drugs on the pharmacokinetics
Warfarin: There was no clinically significant effect of a single dose of warfarin 25 mg on the pharmacokinetics of aliskiren.
Figure 2: The impact of aliskiren on the pharmacokinetics
of co-administered drugs.
Amlodipine is extensively (about 90%) converted to inactive metabolites via hepatic metabolism, with 10% of the parent compound and 60% of the metabolites excreted in the urine.
Elimination of amlodipine from the plasma is biphasic, with a terminal elimination half-life of about 30-50 hours.
HCTZ is not metabolized but is eliminated rapidly by the kidney. At least 61% of the oral dose is eliminated as unchanged drug within 24 hours. The elimination half-life is between 5.8 and 18.9 hours.
The pharmacokinetics of Amturnide have not been investigated in patients < 18 years of age.
The pharmacokinetics of aliskiren were studied in the elderly ( ≥ 65 years). Exposure (measured by AUC) is increased in elderly patients. Adjustment of the starting dose of aliskiren is not required in these patients [see DOSAGE AND ADMINISTRATION].
Elderly patients have decreased clearance of amlodipine, with a resulting increase in AUC of approximately 40%-60%; therefore, a lower initial dose of amlodipine may be required [see DOSAGE AND ADMINISTRATION].
With Amturnide, pharmacokinetic differences due to race have not been studied. The pharmacokinetic differences among Blacks, Caucasians, and Japanese are minimal with aliskiren therapy.
The pharmacokinetics of aliskiren were evaluated in patients with varying degrees of renal impairment. Rate and extent of exposure (AUC and Cmax) of aliskiren in subjects with renal impairment did not show a consistent correlation with the severity of renal impairment. Adjustment of the starting dose is not required in patients with mild to moderate renal impairment, but Amturnide is not recommended in patients with severe renal impairment [see DOSAGE AND ADMINISTRATION and WARNINGS AND PRECAUTIONS].
The pharmacokinetics of amlodipine is not significantly influenced by renal impairment. Patients with renal failure may therefore receive the usual initial dose [see DOSAGE AND ADMINISTRATION].
The pharmacokinetics of aliskiren were not significantly affected in patients with mild-to-severe liver disease. Consequently, adjustment of the starting dose is not required in these patients [see DOSAGE AND ADMINISTRATION].
Patients with hepatic insufficiency have decreased clearance of amlodipine with resulting increase in AUC of approximately 40%-60%. A lower initial dose of amlodipine is required for patients with severe hepatic impairment [see DOSAGE AND ADMINISTRATION].
Animal Toxicology and/or Pharmacology
Reproductive Toxicology Studies
[See Use In Specific Populations.]
Amturnide was studied in a double-blind, active-controlled study in 1181 treated hypertensive patients, of whom 773 were classified as moderately hypertensive (SBP 160-180 mmHg) and 408 as severely hypertensive (SBP 180-200 mmHg) at baseline. The mean baseline systolic/diastolic blood pressure for all randomized patients was approximately 173/105 mmHg. A total of 61% of patients were male, 19% were 65 years or older, 84% were Caucasian, and 10% were Black.
At study initiation, patients assigned to the dual combination treatments received lower doses of their treatment combination (aliskiren 150 mg plus amlodipine 5 mg, aliskiren 150 mg plus HCTZ 12.5 mg, or amlodipine 5 mg plus HCTZ 12.5 mg), while patients assigned to the Amturnide arm received aliskiren/HCTZ 150/12.5 mg. After 3 days, Amturnide patients were titrated to aliskiren/amlodipine/HCTZ 150/5/12.5 mg, while all other patients continued receiving their initial doses. After 4 weeks, all patients were titrated to their full target doses of aliskiren/amlodipine/HCTZ 300/10/25 mg, aliskiren/amlodipine 300/10, aliskiren/HCTZ 300/25 mg, or amlodipine/HCTZ 10/25 mg.
Amturnide produced greater reductions in blood pressure than did any of the 3 dual combination treatments (p < 0.001 for both diastolic and systolic blood pressure reductions). The reductions in systolic/diastolic blood pressure with Amturnide were 9.9/6.3 mmHg greater than with aliskiren/HCTZ, 7.2/3.6 mmHg greater than with amlodipine/HCTZ, and 6.6/2.6 mmHg greater than with aliskiren/amlodipine.
In the severe hypertensive patients, Amturnide produced greater reductions in blood pressure than each of the 3 dual combination treatments (p < 0.001 for both diastolic and systolic blood pressure reductions). The reductions in systolic/diastolic blood pressure with Amturnide were 16.3/8.2 mmHg greater than with aliskiren/HCTZ, 9.6/4.8 mmHg greater than with amlodipine/HCTZ, and 11.4/4.9 mmHg greater than with aliskiren/amlodipine.
The distribution of reductions in blood pressure on each treatment are shown in Figure 3 for diastolic blood pressure and in Figure 4 for systolic blood pressure. For example, Figure 3 shows that 50% of patients on Amturnide had more than 20.2 mmHg reduction in diastolic blood pressure compared to 18.7 mmHg on aliskiren/amlodipine combination, 12.7 mmHg on aliskiren/HCTZ combination, and 15.3 mmHg on amlodipine/HCTZ combination. Similarly, Figure 4 shows that 50% of patients on Amturnide had more than 36.3 mmHg reduction in systolic blood pressure compared to 30.8 mmHg on aliskiren/amlodipine combination, 28.3 mmHg on aliskiren/HCTZ combination, and 31.0 mmHg on amlodipine/HCTZ combination. The time course over which blood pressure effects developed is shown in Figures 5 and 6. As the trial had no placebo control, the treatment effects shown in Figures 3-6 include a placebo effect of unknown size.
Figure 3: Distribution of diastolic blood pressure
responses on Amturnide and combinations of two drugs.
Figure 4: Distribution of systolic blood pressure
responses on Amturnide and combinations of two drugs.
Figure 5: Mean Ambulatory Diastolic Blood Pressure at
Endpoint by Treatment and Clock Hour
Figure 6: Mean Ambulatory Systolic Blood Pressure at
Endpoint by Treatment and Clock Hour
There are no trials of the Amturnide triple combination tablet demonstrating reductions in cardiovascular risk in patients with hypertension, but two of the components, amlodipine and hydrochlorothiazide, have demonstrated such benefits.
Last reviewed on RxList: 2/15/2012
This monograph has been modified to include the generic and brand name in many instances.
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