CLINICAL PHARMACOLOGY
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 normal or well-compensated patients
with heart failure with agents possessing significant negative inotropic
effects.
Amlodipine does not change sinoatrial nodal function or
atrioventricular (AV) 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 (ECG) 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.
Drug Interactions
Sildenafil
When amlodipine and sildenafil were used in combination,
each agent independently exerted its own blood pressure lowering effect [see
DRUG INTERACTIONS].
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 to
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 to 50 hours. Steady state
plasma levels of amlodipine are reached after 7 to 8 days of consecutive daily
dosing.
Valsartan
Following oral administration of valsartan alone peak
plasma concentrations of valsartan are reached in 2 to 4 hours. Absolute
bioavailability is about 25% (range 10% to 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 biexponential 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. In vitro metabolism studies involving
recombinant CYP 450 enzymes indicated that the CYP 2C9 isoenzyme is responsible
for the formation of valeryl-4-hydroxy valsartan. Valsartan does not inhibit
CYP 450 isozymes at clinically relevant concentrations. CYP 450 mediated drug
interaction between valsartan and coadministered drugs are unlikely because of
the low extent of metabolism.
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 to 8 hours, respectively. The rate and extent of absorption
of valsartan and amlodipine from Exforge are the same as when administered as
individual tablets. The bioavailabilities of amlodipine and valsartan are not
altered by the coadministration of food.
Special Populations
Geriatric
Amlodipine: Elderly patients have decreased
clearance of amlodipine with a resulting increase in peak plasma levels,
elimination half-life and AUC.
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
Valsartan: Pharmacokinetics of valsartan does not
differ significantly between males and females.
Renal Insufficiency
Amlodipine: The pharmacokinetics of amlodipine is
not significantly influenced by renal impairment.
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
Amlodipine: Patients with hepatic insufficiency
have decreased clearance of amlodipine with resulting increase in AUC of
approximately 40% to 60%.
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.
Drug Interactions
In vitro data in human plasma indicate that amlodipine
has no effect on the protein binding of digoxin, phenytoin, warfarin and
indomethacin.
Impact of Other Drugs on Amlodipine
Co-administered cimetidine, magnesium-and aluminum
hydroxide antacids, sildenafil, and grapefruit juice have no impact on the
exposure to amlodipine.
CYP3A inhibitors: Co-administration 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 CYP3A (e.g., itraconazole,
clarithromycin) may increase the plasma concentrations of amlodipine to a
greater extent [see DRUG INTERACTIONS].
Impact of Amlodipine on Other Drugs
Co-administered amlodipine does not affect the exposure
to atorvastatin, digoxin, ethanol and the warfarin prothrombin response time.
Simvastatin: Co-administration 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 [see DRUG INTERACTIONS].
Cyclosporine: A prospective study in renal
transplant patients (N=11) showed on an average of 40% increase in trough
cyclosporine levels when concomitantly treated with amlodipine [see DRUG
INTERACTIONS].
Tacrolimus: A prospective study in healthy Chinese
volunteers (N=9) with CYP3A5 expressers showed a 2.5-to 4-fold increase in
tacrolimus exposure when concomitantly administered with amlodipine compared to
tacrolimus alone. This finding was not observed in CYP3A5 non-expressers (N=
6). However, a 3-fold increase in plasma exposure to tacrolimus in a renal
transplant patient (CYP3A5 non-expresser) upon initiation of amlodipine for the
treatment of post-transplant hypertension resulting in reduction of tacrolimus
dose has been reported. Irrespective of the CYP3A5 genotype status, the
possibility of an interaction cannot be excluded with these drugs [see DRUG
INTERACTIONS].
Developmental Toxicity Studies
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 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.
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.)
Amlodipine Besylate and Valsartan
In the oral embryofetal 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 embryofetal
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 3 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 2 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 |
Valsartan dosage |
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 |
Valsartan dosage |
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 2 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* |
Treatment Difference** |
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 to 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 1 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.
There are no trials of the Exforge combination tablet
demonstrating reductions in cardiovascular risk in patients with hypertension,
but the amlodipine component and several ARBs, which are the same pharmacological
class as the valsartan component, have demonstrated such benefits.