CLINICAL PHARMACOLOGY
Mechanism Of Action
Amturnide
The effects of combined treatment of aliskiren,
amlodipine and HCTZ arise from the actions of these 3 agents on different but
complementary mechanisms that regulate blood pressure. Together, inhibition of
the RAAS, inhibition of calcium channel-mediated vasoconstriction, and increase
of sodium chloride excretion lowers blood pressure to a greater degree than the
individual components.
Aliskiren
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 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
ACEIs 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
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.
Amlodipine is a peripheral arterial vasodilator that acts
directly on vascular smooth muscle to cause a reduction in peripheral vascular
resistance and reduction in blood pressure.
HCTZ
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.
Pharmacodynamics
Amturnide
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.
Aliskiren
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.
Amlodipine
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 mmHg to 114 mmHg) had about 50% greater response than
patients with mild hypertension (diastolic pressure 90 mmHg to 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 coadministered 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.
HCTZ
After oral administration of HCTZ, diuresis begins within
2 hours, peaks in about 4 hours, and lasts about 6 to 12 hours.
Drug Interactions
Hydrochlorothiazide (HCTZ)
Alcohol, barbiturates, or narcotics: Potentiation
of orthostatic hypotension may occur.
Skeletal muscle relaxants: Possible increased
responsiveness to muscle relaxants such as curare derivatives.
Digitalis glycosides: Thiazide-induced hypokalemia
or hypomagnesemia may predispose the patient to digoxin toxicity.
Pharmacokinetics
Absorption and Distribution
Amturnide
Following oral administration of the fixed combination of
aliskiren, amlodipine, and HCTZ, peak concentrations were achieved within 1 to
2 hours, 6 to 12 hours, and 1 to 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
Aliskiren is poorly absorbed (bioavailability about
2.5%). Following oral administration, peak plasma concentrations of aliskiren
are reached within 1 to 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 of aliskiren, it was administered without requiring a fixed relation of
administration to meals.
Amlodipine
Peak plasma concentrations of amlodipine are reached 6 to
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.
The apparent volume of distribution of amlodipine is
about 21 L/kg. Approximately 93% of circulating amlodipine is bound to plasma
proteins in hypertensive patients.
HCTZ
The estimated absolute bioavailability of HCTZ after oral
administration is about 70%. Peak plasma HCTZ concentrations (Cmax) are reached
within 2 to 5 hours after oral administration. There is no clinically
significant effect of food on the bioavailability of HCTZ.
HCTZ binds to albumin (40% to 70%) and distributes into
erythrocytes. Following oral administration, plasma hydrochlorothiazide
concentrations decline bi-exponentially, with a mean distribution half-life of
about 2 hours and an elimination half-life of about 10 hours.
Metabolism and Elimination
Aliskiren
The effective half-life for aliskiren is 24 hours. Steady
state blood levels are reached in about 7 to 8 days. 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 CYP3A4. Aliskiren does not
inhibit the CYP450 isoenzymes (CYP 1A2, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A) or
induce CYP3A4.
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.
Amlodipine
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 to 50 hours. Steady state
plasma levels are reached after once-daily dosing for 7 to 8 days.
HCTZ
About 70% of an orally administered dose of HCTZ is
eliminated in the urine as unchanged drug.
Drug Interactions
Aliskiren
The effects of coadministered 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 coadministered drugs on
aliskiren) and Figure 2 (impact of aliskiren on coadministered drugs).
Figure 1: The Impact of Coadministered Drugs on the
Pharmacokinetics of Aliskiren
*Ketoconazole: A 400 mg once daily dose was not studied,
but would be expected to increase aliskiren blood levels further.
**Ramipril, valsartan, irbesartan: In general, avoid
combined use of aliskiren with ACE inhibitors or ARBs, particularly in patients
with CrCl less than 60 mL/min [see DRUG INTERACTIONS].
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 Coadministered Drugs
*Furosemide: Patients receiving furosemide may find its
effects diminished after starting aliskiren. In patients with heart failure,
coadministration of aliskiren (300 mg/day) reduced plasma AUC and Cmax of oral
furosemide (60 mg/day) by 17% and 27%, respectively, and reduced 24 hour
urinary furosemide excretion by 29%. This change in exposure did not result in
statistically significant difference in total urine volume and urinary sodium
excretion over 24 hours. However, a transient decrease in urinary sodium
excretion and urine volume effects up to 12 hours were observed when furosemide
was coadministered with aliskiren 300 mg/day.
**Ramipril, valsartan: In general, avoid combined use of
aliskiren with ACE inhibitors or ARBs, particularly in patients with CrCl less
than 60 mL/min [see DRUG INTERACTIONS].
Amlodipine
In vitro data in human plasma indicate that amlodipine
has no effect on the protein binding of digoxin, phenytoin, warfarin, and
indomethacin.
Cimetidine: Coadministration of amlodipine with
cimetidine did not alter the pharmacokinetics of amlodipine.
Grapefruit juice: Coadministration of 240 mL of
grapefruit juice with a single oral dose of amlodipine 10 mg in 20 healthy
volunteers had no significant effect on the pharmacokinetics of amlodipine.
Maalox® (antacid): Coadministration of the antacid
Maalox with a single dose of amlodipine had no significant effect on the
pharmacokinetics of amlodipine.
Sildenafil: A single 100 mg dose of sildenafil in
subjects with essential hypertension had no effect on the pharmacokinetic
parameters of amlodipine. When amlodipine and sildenafil were used in
combination, each agent independently exerted its own blood pressure lowering
effect.
Atorvastatin: Coadministration of multiple 10 mg
doses of amlodipine with 80 mg of atorvastatin resulted in no significant
change in the steady-state pharmacokinetic parameters of atorvastatin.
Digoxin: Coadministration of amlodipine with
digoxin did not change serum digoxin levels or digoxin renal clearance in
normal volunteers.
Ethanol (alcohol): Single and multiple 10 mg doses
of amlodipine had no significant effect on the pharmacokinetics of ethanol.
Warfarin: Coadministration of amlodipine with
warfarin did not change the warfarin prothrombin response time.
Simvastatin: Coadministration of multiple doses of
10 mg of amlodipine with 80 mg simvastatin resulted in a 77% increase in
exposure to simvastatin compared to simvastatin alone.
CYP3A inhibitors: Coadministration of a 180 mg
daily dose of diltiazem with 5 mg amlodipine in elderly hypertensive patients
resulted in a 60% increase in amlodipine systemic exposure. Erythromycin
coadministration in healthy volunteers did not significantly change amlodipine
systemic exposure. However, strong inhibitors of CYP3A4 (e.g., ketoconazole,
itraconazole, ritonavir) may increase the plasma concentrations of amlodipine
to a greater extent.
Hydrochlorothiazide (HCTZ)
Drugs that alter gastrointestinal motility: The
bioavailability of thiazide-type diuretics may be increased by anticholinergic
agents (e.g. atropine, biperiden), apparently due to a decrease in
gastrointestinal motility and the stomach emptying rate. Conversely,
pro-kinetic drugs may decrease the bioavailability of thiazide diuretics.
Cholestyramine: In a dedicated drug interaction
study, administration of cholestyramine 2 hours before HCTZ resulted in a 70%
reduction in exposure to HCTZ. Further, administration of HCTZ 2 hours before
cholestyramine, resulted in 35% reduction in exposure to hydrochlorothiazide.
Antineoplastic agents (e.g., cyclophosphamide,
methotrexate): Concomitant use of thiazide diuretics may reduce renal
excretion of cytotoxic agents and enhance their myelosuppressive effects.
Special Populations
Pediatric Patients
The pharmacokinetics of Amturnide have not been
investigated in patients younger than 18 years of age.
Geriatric Patients
Impact of aging on aliskiren pharmacokinetics has been
assessed. When compared to young adults (18 to 40 years), aliskiren mean AUC
and Cmax in elderly subjects (65 years and older) are increased by 57% and 28%,
respectively. In the elderly, clearance of amlodipine is decreased with
resulting increases in peak plasma levels, elimination half-life and
area-under-the-plasma-concentration curve. Limited data suggest that the
systemic clearance of HCTZ is reduced in both healthy and hypertensive elderly
subjects compared to young healthy volunteers [see Use in Specific
Populations].
Race
With Amturnide, pharmacokinetic differences due to race
have not been studied. The pharmacokinetic differences among blacks,
Caucasians, and Japanese are minimal with aliskiren therapy.
Hepatic Impairment
The pharmacokinetics of aliskiren is not significantly
affected in patients with mild-to-severe liver disease. Patients with hepatic
insufficiency have decreased clearance of amlodipine with resulting increase in
AUC of approximately 40% to 60% [see WARNINGS AND PRECAUTIONS and Use
in Specific Populations].
Renal Impairment
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.
The pharmacokinetics of aliskiren following
administration of a single oral dose of 300 mg was evaluated in patients with
End Stage Renal Disease (ESRD) undergoing hemodialysis. When compared to
matched healthy subjects, changes in the rate and extent of aliskiren exposure
(Cmax and AUC) in ESRD patients undergoing hemodialysis were not clinically
significant. Timing of hemodialysis did not significantly alter the pharmacokinetics
of aliskiren in ESRD patients.
The pharmacokinetics of amlodipine is not significantly
influenced by renal impairment.
In a study in individuals with impaired renal function,
the mean elimination half-life of HCTZ was doubled in individuals with
mild/moderate renal impairment (30 < CrCl < 90 mL/min) and tripled in
severe renal impairment (CrCl less than or equal to 30 mL/min), compared to
individuals with normal renal function (CrCl greater than 90 mL/min) [see WARNINGS
AND PRECAUTIONS and Use In Specific Populations].
Animal Toxicology And/Or Pharmacology
Reproductive Toxicology Studies
[See Use In Specific Populations]
Clinical Studies
Amturnide
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 to 180 mmHg) and 408 as severely
hypertensive (SBP 180 to 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 value less than 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 value less than 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.
The antihypertensive effect of Amturnide was similar in
patients with and without diabetes, obese and non-obese patients, in patients
65 years of age and older and less than 65 years of age, and in women and men.
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 2 of the components, amlodipine and HCTZ, have demonstrated such benefits.
Aliskiren In Patients With Diabetes treated With ARB Or ACEI
(ALTITUDE study)
Patients with diabetes with renal disease (defined either
by the presence of albuminuria or reduced GFR) were randomized to aliskiren 300
mg daily (n=4296) or placebo (n=4310). All patients were receiving background
therapy with an ARB or ACEI. The primary efficacy outcome was the time to the
first event of the primary composite endpoint consisting of cardiovascular
death, resuscitated sudden death, nonfatal myocardial infarction, nonfatal
stroke, unplanned hospitalization for heart failure, onset of end stage renal
disease, renal death, and doubling of serum creatinine concentration from
baseline sustained for at least 1 month. After a median follow up of about 32
months, the trial was terminated early for lack of efficacy. Higher risk of
renal impairment, hypotension and hyperkalemia was observed in aliskiren
compared to placebo treated patients, as shown in Table 2.
Table 2: Incidence of Selected Adverse Events During
the Treatment Phase in ALTITUDE
|
Aliskiren
N=4272 |
Placebo
N=4285 |
Serious Adverse Events* (%) |
Adverse Events (%) |
Serious Adverse Events* (%) |
Adverse Events (%) |
Renal impairment † |
5.7 |
14.5 |
4.3 |
12.4 |
Hypotension †† |
2.3 |
19.9 |
1.9 |
16.3 |
Hyperkalemia††† |
1.0 |
38.9 |
0.5 |
28.8 |
†renal failure, renal failure acute, renal failure chronic,
renal impairment
††dizziness, dizziness postural, hypotension, orthostatic hypotension,
presyncope, syncope
††† Given the variable baseline potassium levels of patients with renal
insufficiency on dual RAAS therapy, the reporting of adverse event of
hyperkalemia was at the discretion of the investigator.
* A Serious Adverse Event (SAE) is defined as: an event which is fatal or
life-threatening, results in persistent or significant disability/incapacity,
constitutes a congenital anomaly/birth defect, requires inpatient
hospitalization or prolongation of existing hospitalization, or is medically
significant (i.e., defined as an event that jeopardizes the patient or may
require medical or surgical intervention to prevent one of the outcomes
previously listed). |
The risk of stroke (3.4% aliskiren versus 2.7% placebo)
and death (8.4% aliskiren versus 8.0% placebo) were also numerically higher in
aliskiren treated patients.