Mechanism of Action
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.
Valsartan
Angiotensin II is formed from angiotensin I in a reaction catalyzed by angiotensin-converting
enzyme (ACE, kininase 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. Valsartan blocks the vasoconstrictor and aldosterone-secreting 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 pathways for angiotensin
II synthesis.
There is also an AT2 receptor found in many tissues, but AT2
is not known to be associated with cardiovascular homeostasis. Valsartan has
much greater affinity (about 20,000-fold) for the AT1 receptor than
for the AT2 receptor. The increased plasma levels of angiotensin
following AT1 receptor blockade with valsartan may stimulate the
unblocked AT2 receptor. The primary metabolite of valsartan is essentially
inactive with an affinity for the AT1 receptor about one-200th that
of valsartan itself.
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 also catalyzed by ACE. Because valsartan does not inhibit ACE (kininase
II), it does not affect the response to bradykinin. Whether this difference
has clinical relevance is not yet known. Valsartan does not bind to or block
other hormone 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
valsartan on blood pressure.
Pharmacodynamics
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 105-114 mmHg) had about a 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 the therapeutic
dose range to intact animals and man, even when coadministered with beta-blockers
to man. Similar findings, however, have been observed in normals 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.
Valsartan
Valsartan inhibits the pressor effect of angiotensin II infusions. An oral
dose of 80 mg inhibits the pressor effect by about 80% at peak with approximately
30% inhibition persisting for 24 hours. No information on the effect of larger
doses is available.
Removal of the negative feedback of angiotensin II causes a 2- to 3-fold rise
in plasma renin and consequent rise in angiotensin II plasma concentration in
hypertensive patients. Minimal decreases in plasma aldosterone were observed
after administration of valsartan; very little effect on serum potassium was
observed.
In multiple dose studies in hypertensive patients with stable renal insufficiency
and patients with renovascular hypertension, valsartan had no clinically significant
effects on glomerular filtration rate, filtration fraction, creatinine clearance,
or renal plasma flow.
Administration of valsartan to patients with essential hypertension results
in a significant reduction of sitting, supine, and standing systolic blood pressure,
usually with little or no orthostatic change.
Valsartan has indications other than hypertension which can be found in the
Diovan® package insert.
Exforge
Exforge has been shown to be effective in lowering blood pressure. Both amlodipine
and valsartan lower blood pressure by reducing peripheral resistance, but calcium
influx blockade and reduction of angiotensin II vasoconstriction are complementary
mechanisms.
Pharmacokinetics
Amlodipine
Peak plasma concentrations of amlodipine are reached 6-12 hours after administration
of amlodipine alone. 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 21 L/kg. Approximately
93% of circulating amlodipine is bound to plasma proteins in hypertensive patients.
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. Steady state plasma levels of amlodipine are
reached after 7-8 days of consecutive daily dosing.
Valsartan
Following oral administration of valsartan alone peak plasma concentrations
of valsartan are reached in 2-4 hours. Absolute bioavailability is about 25%
(range 10%-35%). Food decreases the exposure (as measured by AUC) to valsartan
by about 40% and peak plasma concentration (Cmax) by about 50%.
The steady state volume of distribution of valsartan after intravenous administration
is 17 L indicating that valsartan does not distribute into tissues extensively.
Valsartan is highly bound to serum proteins (95%), mainly serum albumin.
Valsartan shows bi-exponential decay kinetics following intravenous administration
with an average elimination half-life of about 6 hours. The recovery is mainly
as unchanged drug, with only about 20% of dose recovered as metabolites. The
primary metabolite, accounting for about 9% of dose, is valeryl 4-hydroxy valsartan.
The enzyme(s) responsible for valsartan metabolism have not been identified
but do not seem to be CYP 450 isoenzymes.
Valsartan, when administered as an oral solution, is primarily recovered in
feces (about 83% of dose) and urine (about 13% of dose). Following intravenous
administration, plasma clearance of valsartan is about 2 L/h and its renal clearance
is 0.62 L/h (about 30% of total clearance).
Exforge
Following oral administration of Exforge in normal healthy adults, peak plasma
concentrations of valsartan and amlodipine are reached in 3 and 6-8 hours, respectively.
The rate and extent of absorption of valsartan and amlodipine from Exforge are
the same as when administered as individual tablets.
Special Populations
Geriatric
Studies with Amlodipine: 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.
Studies with Valsartan: Exposure (measured by AUC) to valsartan
is higher by 70% and the half-life is longer by 35% in the elderly than in the
young. No dosage adjustment is necessary.
Gender
Studies with Valsartan: Pharmacokinetics of valsartan does not
differ significantly between males and females.
Renal Insufficiency
Studies with Amlodipine: The pharmacokinetics of amlodipine is
not significantly influenced by renal impairment. Patients with renal failure
may therefore receive the usual initial dose.
Studies with Valsartan: There is no apparent correlation between
renal function (measured by creatinine clearance) and exposure (measured by
AUC) to valsartan in patients with different degrees of renal impairment. Consequently,
dose adjustment is not required in patients with mild-to-moderate renal dysfunction.
No studies have been performed in patients with severe impairment of renal function
(creatinine clearance < 10 mL/min). Valsartan is not removed from the plasma
by hemodialysis. In the case of severe renal disease, exercise care with dosing
of valsartan.
Hepatic Insufficiency
Studies with Amlodipine: Patients with hepatic insufficiency
have decreased clearance of amlodipine with resulting increase in AUC of approximately
40%-60%; therefore, a lower initial dose of amlodipine may be required.
Studies with Valsartan: On average, patients with mild-to-moderate
chronic liver disease have twice the exposure (measured by AUC values) to valsartan
of healthy volunteers (matched by age, sex and weight). In general, no dosage
adjustment is needed in patients with mild-to-moderate liver disease. Care should
be exercised in patients with liver disease.
Animal Toxicology and/or Pharmacology
Reproductive Toxicology Studies
Valsartan had no adverse effects on the reproductive performance of male or
female rats at oral doses of up to 200 mg/kg/day. This dose is about 6 times
the maximum recommended human dose on a mg/m² basis.
Studies with 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 mg/m² 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.
Studies with Valsartan
No teratogenic effects were observed when valsartan was administered to pregnant
mice and rats at oral doses of up to 600 mg/kg/day and to pregnant rabbits at
oral doses of up to 10 mg/kg/day. However, significant decreases in fetal weight,
pup birth weight, pup survival rate, and slight delays in developmental milestones
were observed in studies in which parental rats were treated with valsartan
at oral, maternally toxic (reduction in body weight gain and food consumption)
doses of 600 mg/kg/day during organogenesis or late gestation and lactation.
In rabbits, fetotoxicity (i.e., resorptions, litter loss, abortions, and low
body weight) associated with maternal toxicity (mortality) was observed at doses
of 5 and 10 mg/kg/day. The no observed adverse effect doses of 600, 200 and
2 mg/kg/day in mice, rats and rabbits, respectively, are about 9, 6 and 0.1
times the MRHD of 320 mg/day on a mg/m² basis. (Calculations based on a
patient weight of 60 kg.)
Studies with Amlodipine Besylate and Valsartan
In the oral embryo-fetal development study in rats using amlodipine besylate
plus valsartan at doses equivalent to 5 mg/kg/day amlodipine plus 80 mg/kg/day
valsartan, 10 mg/kg/day amlodipine plus 160 mg/kg/day valsartan, and 20 mg/kg/day
amlodipine plus 320 mg/kg/day valsartan, treatment-related maternal and fetal
effects (developmental delays and alterations noted in the presence of significant
maternal toxicity) were noted with the high dose combination. The no-observed-adverse-effect
level (NOAEL) for embryo-fetal effects was 10 mg/kg/day amlodipine plus 160
mg/kg/day valsartan. On a systemic exposure [AUC(0-∞)] basis,
these doses are, respectively, 4.3 and 2.7 times the systemic exposure [AUC(0-∞)]
in humans receiving the MRHD (10/320 mg/60 kg).
Clinical Studies
Exforge was studied in 2 placebo-controlled and 4 active-controlled trials
in hypertensive patients. In a double-blind, placebo controlled study, a total
of 1012 patients with mild-to-moderate hypertension received treatments of three
combinations of amlodipine and valsartan (5/80, 5/160, 5/320 mg) or amlodipine
alone (5 mg), valsartan alone (80, 160, or 320 mg) or placebo. All doses with
the exception of the 5/320 mg dose were initiated at the randomized dose. The
high dose was titrated to that dose after a week at a dose of 5/160 mg. At week
8, the combination treatments were statistically significantly superior to their
monotherapy components in reduction of diastolic and systolic blood pressures.
Table 1: Effect of Exforge on Sitting Diastolic Blood Pressure
| Amlodipine dosage |
Valsartan dosage |
| 0 mg |
80 mg |
160 mg |
320 mg |
| Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
| 0 mg |
-6.4 |
|
-9.5 |
-3.1 |
-10.9 |
-4.5 |
-13.2 |
-6.7 |
| 5 mg |
-11.1 |
-4.7 |
-14.2 |
-7.8 |
-14.0 |
-7.6 |
-15.7 |
-9.3 |
| *Mean Change and Placebo-Subtracted Mean
Change from Baseline (mmHg) at Week 8 in Sitting Diastolic Blood Pressure.
Mean baseline diastolic BP was 99.3 mmHg. |
Table 2: Effect of Exforge on Sitting Systolic Blood Pressure
| Amlodipine dosage |
Valsartan dosage |
| 0 mg |
80 mg |
160 mg |
320 mg |
| Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
| 0 mg |
-6.2 |
- |
-12.9 |
-6.8 |
-14.3 |
-8.2 |
-16.3 |
-10.1 |
| 5 mg |
-14.8 |
-8.6 |
-20.7 |
-14.5 |
-19.4 |
-13.2 |
-22.4 |
-16.2 |
| *Mean Change and Placebo-Subtracted Mean
Change from Baseline (mmHg) at Week 8 in Sitting Systolic Blood Pressure.
Mean baseline systolic BP was 152.8 mmHg. |
In a double-blind, placebo controlled study, a total of 1246 patients with
mild to moderate hypertension received treatments of two combinations of amlodipine
and valsartan (10/160, 10/320 mg) or amlodipine alone (10 mg), valsartan alone
(160 or 320 mg) or placebo. With the exception of the 10/320 mg dose, treatment
was initiated at the randomized dose. The high dose was initiated at a dose
of 5/160 mg and titrated to the randomized dose after 1 week. At week 8, the
combination treatments were statistically significantly superior to their monotherapy
components in reduction of diastolic and systolic blood pressures.
Table 3: Effect of Exforge on Sitting Diastolic Blood Pressure
| Amlodipine dosage |
Valsartandosage |
| 0 mg |
160 mg |
320 mg |
| Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
| 0 mg |
-8.2 |
-- |
-12.8 |
- 4.5 |
-12.8 |
-4.5 |
| 10 mg |
-15.0 |
-6.7 |
- 17.2 |
- 9.0 |
-18.1 |
-9.9 |
| *Mean Change and Placebo-Subtracted Mean
Change from Baseline (mmHg) at Week 8 in Sitting Diastolic Blood Pressure.
Mean baseline diastolic BP was 99.1 mmHg. |
Table 4: Effect of Exforge on Sitting Systolic Blood Pressure
| Amlodipine dosage |
Valsartandosage |
| 0 mg |
160 mg |
320 mg |
| Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
Mean Change* |
Placebo- subtracted |
| 0 mg |
-11.0 |
|
-18.1 |
-7.0 |
-18.5 |
-7.5 |
| 10 mg |
-22.2 |
-11.2 |
-26.6 |
-15.5 |
-26.9 |
-15.9 |
| *Mean Change and Placebo-Subtracted Mean
Change from Baseline (mmHg) at Week 8 in Sitting Systolic Blood Pressure.
Mean baseline systolic BP was 156.7 mmHg. |
In a double-blind, active-controlled study, a total of 947 patients with mild
to moderate hypertension who were not adequately controlled on valsartan 160
mg received treatments of two combinations of amlodipine and valsartan (10/160,
5/160 mg), or valsartan alone (160 mg). At week 8, the combination treatments
were statistically significantly superior to the monotherapy component in reduction
of diastolic and systolic blood pressures.
Table 5: Effect of Exforge on Sitting Diastolic/Systolic
Blood Pressure
| Treatment Group |
Diastolic BP |
Systolic BP |
| Mean change* |
Treatment Difference** |
Mean change* Difference** |
Treatment |
| Exforge 10/160 mg |
-11.4 |
-4.8 |
-13.9 |
-5.7 |
| Exforge 5/160 mg |
-9.6 |
-3.1 |
-12.0 |
-3.9 |
| Valsartan 160 mg |
-6.6 |
|
-8.2 |
-- |
*Mean Change from Baseline at Week 8 in
Sitting Diastolic/Systolic Blood Pressure. Mean baseline BP was 149.5/
96.5 (systolic/diastolic) mmHg
**Treatment Difference = difference in mean BP reduction between Exforge
and the control group (Valsartan 160 mg) |
In a double-blind, active-controlled study, a total of 944 patients with mild
to moderate hypertension who were not adequately controlled on amlodipine 10
mg received a combination of amlodipine and valsartan (10/160 mg), or amlodipine
alone (10 mg). At week 8, the combination treatment was statistically significantly
superior to the monotherapy component in reduction of diastolic and systolic
blood pressures.
Table 6: Effect of Exforge on Sitting Diastolic/Systolic
Blood Pressure
| Treatment Group |
Diastolic BP |
Systolic BP |
| Mean change* |
Treatment Difference** |
Mean change* |
Treatment Difference** |
| Exforge 10/160 mg |
-11.8 |
-1.8 |
-12.7 |
-1.9 |
| Amlodipine 10 mg |
-10.0 |
-- |
-10.8 |
-- |
*Mean Change from Baseline at Week 8 in
Sitting Diastolic/Systolic Blood Pressure. Mean baseline BP was 147.0/
95.1 (systolic/diastolic) mmHg
**Treatment Difference = difference in mean BP reduction between Exforge
and the control group (Amlodipine 10 mg) |
Exforge was also evaluated for safety in a 6-week, double-blind, active-controlled
trial of 130 hypertensive patients with severe hypertension (mean baseline BP
of 171/113 mmHg). Adverse events were similar in patients with severe hypertension
and mild/moderate hypertension treated with Exforge.
A wide age range of the adult population, including the elderly was studied
(range 19-92 years, mean 54.7 years). Women comprised almost half of the studied
population (47.3%). Of the patients in the studied Exforge group, 87.6% were
Caucasian. Black and Asian patients each represented approximately 4% of the
population in the studied Exforge group.
Two additional double-blind, active-controlled studies were conducted in which
Exforge was administered as initial therapy. In one study, a total of 572 Black
patients with moderate to severe hypertension were randomized to receive either
combination amlodipine/valsartan or amlodipine monotherapy for 12 weeks. The
initial dose of amlodipine/valsartan was 5/160 mg for 2 weeks with forced titration
to 10/160 mg for 2 weeks, followed by optional titration to 10/320 mg for 4
weeks and optional addition of HCTZ 12.5 mg for 4 weeks. The initial dose of
amlodipine was 5 mg for 2 weeks with forced titration to 10 mg for 2 weeks,
followed by optional titration to 10 mg for 4 weeks and optional addition of
HCTZ 12.5 mg for 4 weeks. At the primary endpoint of 8 weeks, the treatment
difference between amlodipine/valsartan and amlodipine was 6.7/2.8 mmHg.
In the other study of similar design, a total of 646 patients with moderate
to severe hypertension (MSSBP of ≥ 160 mmHg and < 200 mmHg) were randomized
to receive either combination amlodipine/valsartan or amlodipine monotherapy
for 8 weeks. The initial dose of amlodipine/valsartan was 5/160 mg for 2 weeks
with forced titration to 10/160 mg for 2 weeks, followed by the optional addition
of HCTZ 12.5 mg for 4 weeks. The initial dose of amlodipine was 5 mg for 2 weeks
with forced titration to 10 mg for 2 weeks, followed by the optional addition
of HCTZ 12.5 mg for 4 weeks. At the primary endpoint of 4 weeks, the treatment
difference between amlodipine/valsartan and amlodipine was 6.6/3.9 mmHg.
Last updated on RxList: 9/2/2008