CLINICAL PHARMACOLOGY
Mechanism Of Action
Amlodipine is a dihydropyridine
calcium antagonist (calcium ion antagonist or slow-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.
The precise mechanisms by which
amlodipine relieves angina have not been fully delineated, but are thought to
include the following:
Exertional Angina
In patients with exertional
angina, amlodipine reduces the total peripheral resistance (afterload) against
which the heart works and reduces the rate pressure product, and thus
myocardial oxygen demand, at any given level of exercise.
Vasospastic Angina
Amlodipine has been
demonstrated to block constriction and restore blood flow in coronary arteries
and arterioles in response to calcium, potassium epinephrine, serotonin, and
thromboxane A2 analog in experimental animal models and in human coronary
vessels in vitro. This inhibition of coronary spasm is responsible for the
effectiveness of amlodipine in vasospastic (Prinzmetal's or variant) angina.
Pharmacodynamics
Hemodynamics
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 oral 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
pressures (+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 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.
Electrophysiologic 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 on 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.
Pharmacokinetics
The exposure (Cmax and AUC) of KATERZIA oral suspension
is similar to that of Norvasc® tablet.
Absorption
After oral administration of therapeutic doses of
amlodipine, absorption produces peak plasma concentrations between 6 and 12
hours. Absolute bioavailability has been estimated to be between 64 and 90%.
Effect Of Food
Compared to fasted state administration, standard
high-fat, high-calorie breakfast did not have a significant effect on the
absorption of KATERZIA.
Distribution
Ex vivo studies have shown that approximately 93% of the
circulating drug is bound to plasma proteins in hypertensive patients.
Metabolism
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.
Excretion
Elimination 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 to 8 days of consecutive daily dosing.
Specific Populations
Pediatric Patients
Sixty-two hypertensive patients aged 6 to 17 years
received doses of amlodipine between 1.25 mg and 20 mg. Weight-adjusted
clearance and volume of distribution were similar to values in adults.
Renal Impairment
The pharmacokinetics of amlodipine are not significantly
influenced by renal impairment. Patients with renal failure may therefore
receive the usual initial dose.
Hepatic Impairment
Elderly patients and patients with hepatic insufficiency
have decreased clearance of amlodipine with a resulting increase in AUC of
approximately 40–60%, and a lower initial dose may be required. A similar
increase in AUC was observed in patients with moderate to severe heart failure.
Drug Interactions
In vitro data indicate that amlodipine has no effect on
the human plasma 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 co-administration 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
Amlodipine is a weak inhibitor of CYP3A and may increase
exposure to CYP3A substrates.
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].
Clinical Studies
Effects In Hypertension
Adult Patients
The antihypertensive efficacy of amlodipine has been
demonstrated in a total of 15 double-blind, placebo-controlled, randomized
studies involving 800 patients on amlodipine and 538 on placebo. Once daily
administration produced statistically significant placebo-corrected reductions
in supine and standing blood pressures at 24 hours postdose, averaging about
12/6 mmHg in the standing position and 13/7 mmHg in the supine position in
patients with mild to moderate hypertension. Maintenance of the blood pressure
effect over the 24-hour dosing interval was observed, with little difference in
peak and trough effect. Tolerance was not demonstrated in patients studied for
up to 1 year. The 3 parallel, fixed dose, dose response studies showed that the
reduction in supine and standing blood pressures was dose-related within the
recommended dosing range. Effects on diastolic pressure were similar in young
and older patients. The effect on systolic pressure was greater in older
patients, perhaps because of greater baseline systolic pressure. Effects were
similar in black patients and in white patients.
Pediatric Patients
Two hundred sixty-eight hypertensive patients aged 6 to
17 years were randomized first to amlodipine 2.5 or 5 mg once daily for 4 weeks
and then randomized again to the same dose or to placebo for another 4 weeks.
Patients receiving 2.5 mg or 5 mg at the end of 8 weeks had significantly lower
systolic blood pressure than those secondarily randomized to placebo. The
magnitude of the treatment effect is difficult to interpret, but it is probably
less than 5 mmHg systolic on the 5 mg dose and 3.3 mmHg systolic on the 2.5 mg
dose. Adverse events were similar to those seen in adults.
Effects In Chronic Stable Angina
The effectiveness of 5–10 mg/day of amlodipine in
exercise-induced angina has been evaluated in 8 placebo-controlled,
double-blind clinical trials of up to 6 weeks duration involving 1038 patients
(684 amlodipine, 354 placebo) with chronic stable angina. In 5 of the 8
studies, significant increases in exercise time (bicycle or treadmill) were
seen with the 10 mg dose. Increases in symptom-limited exercise time averaged
12.8% (63 sec) for amlodipine 10 mg, and averaged 7.9% (38 sec) for amlodipine
5 mg. Amlodipine 10 mg also increased time to 1 mm ST segment deviation in
several studies and decreased angina attack rate. The sustained efficacy of
amlodipine in angina patients has been demonstrated over long-term dosing. In
patients with angina, there were no clinically significant reductions in blood
pressures (4/1 mmHg) or changes in heart rate (+0.3 bpm).
Effects In Vasospastic Angina
In a double-blind, placebo-controlled clinical trial of 4
weeks duration in 50 patients, amlodipine therapy decreased attacks by
approximately 4/week compared with a placebo decrease of approximately 1/week
(p<0.01). Two of 23 amlodipine and 7 of 27 placebo patients discontinued
from the study due to lack of clinical improvement.
Effects In Documented Coronary Artery Disease
In PREVENT, 825 patients with angiographically documented
coronary artery disease were randomized to amlodipine (5–10 mg once daily) or
placebo and followed for 3 years. Although the study did not show significance
on the primary objective of change in coronary luminal diameter as assessed by
quantitative coronary angiography, the data suggested a favorable outcome with
respect to fewer hospitalizations for angina and revascularization procedures in
patients with CAD.
CAMELOT enrolled 1318 patients with CAD recently
documented by angiography, without left main coronary disease and without heart
failure or an ejection fraction <40%. Patients (76% males, 89% Caucasian,
93% enrolled at US sites, 89% with a history of angina, 52% without PCI, 4%
with PCI and no stent, and 44% with a stent) were randomized to double-blind
treatment with either amlodipine (5–10 mg once daily) or placebo in addition to
standard care that included aspirin (89%), statins (83%), beta-blockers (74%),
nitroglycerin (50%), anti-coagulants (40%), and diuretics (32%), but excluded
other calcium channel blockers. The mean duration of follow-up was 19 months.
The primary endpoint was the time to first occurrence of one of the following
events: hospitalization for angina pectoris, coronary revascularization,
myocardial infarction, cardiovascular death, resuscitated cardiac arrest,
hospitalization for heart failure, stroke/TIA, or peripheral vascular disease.
A total of 110 (16.6%) and 151 (23.1%) first events occurred in the amlodipine
and placebo groups, respectively, for a hazard ratio of 0.691 (95% CI:
0.540–0.884, p = 0.003). The primary endpoint is summarized in Figure 1 below.
The outcome of this study was largely derived from the prevention of
hospitalizations for angina and the prevention of revascularization procedures
(see Table 1). Effects in various subgroups are shown in Figure 2.
In an angiographic substudy (n=274) conducted within
CAMELOT, there was no significant difference between amlodipine and placebo on
the change of atheroma volume in the coronary artery as assessed by
intravascular ultrasound.
Figure 1 : Kaplan-Meier Analysis of Composite Clinical
Outcomes for Amlodipine versus Placebo
Figure 2 : Effects on
Primary Endpoint of Amlodipine versus Placebo across Sub-Groups
Table 4 below summarizes the
significant composite endpoint and clinical outcomes from the composites of the
primary endpoint. The other components of the primary endpoint including
cardiovascular death, resuscitated cardiac arrest, myocardial infarction,
hospitalization for heart failure, stroke/TIA, or peripheral vascular disease
did not demonstrate a significant difference between amlodipine and placebo.
Table 4: Incidence of Significant Clinical Outcomes
Clinical Outcomes N (%) |
Amlodipine
(N=663) |
Placebo
(N=655) |
Risk Reduction (p-value) |
Composite CV Endpoint |
110 (16.6) |
151 (23.1) |
31% (0.003) |
Hospitalization for Angina* |
51 (7.7) |
84 (12.8) |
42% (0.002) |
Coronary Revascularization* |
78 (11.8) |
103 (15.7) |
27% (0.033) |
* Total patients with these
events |
Studies In Patients With Heart
Failure
Amlodipine has been compared to
placebo in four 8–12 week studies of patients with NYHA Class II/III heart
failure, involving a total of 697 patients. In these studies, there was no
evidence of worsened heart failure based on measures of exercise tolerance,
NYHA classification, symptoms, or left ventricular ejection fraction. In a
long-term (follow-up at least 6 months, mean 13.8 months) placebo-controlled
mortality/morbidity study of amlodipine 5–10 mg in 1153 patients with NYHA
Classes III (n=931) or IV (n=222) heart failure on stable doses of diuretics,
digoxin, and ACE inhibitors, amlodipine had no effect on the primary endpoint
of the study which was the combined endpoint of all-cause mortality and cardiac
morbidity (as defined by life-threatening arrhythmia, acute myocardial
infarction, or hospitalization for worsened heart failure), or on NYHA
classification, or symptoms of heart failure. Total combined all-cause
mortality and cardiac morbidity events were 222/571 (39%) for patients on
amlodipine and 246/583 (42%) for patients on placebo; the cardiac morbid events
represented about 25% of the endpoints in the study.
In another study, (PRAISE-2)
randomized patients with NYHA Class III (80%) or IV (20%) heart failure without
clinical symptoms or objective evidence of underlying ischemic disease, on
stable doses of ACE inhibitors (99%), digitalis (99%), and diuretics (99%), to
placebo (n=827) or amlodipine (n=827) and followed them for a mean of 33
months. There was no statistically significant difference between amlodipine
and placebo in the primary endpoint of all-cause mortality (95% confidence
limits from 8% reduction to 29% increase on amlodipine). With amlodipine there
were more reports of pulmonary edema.