CLINICAL PHARMACOLOGY
Mechanism Of Action
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. Candesartan 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. Candesartan has much greater affinity
( > 10,000-fold) for the AT1 receptor than for the AT2 receptor.
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 candesartan does not inhibit ACE
(kininase II), it does not affect the response to bradykinin. Whether this
difference has clinical relevance is not yet known. Candesartan 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 candesartan on blood pressure.
Pharmacodynamics
Candesartan inhibits the
pressor effects of angiotensin II infusion in a dose-dependent manner. After 1
week of once daily dosing with 8 mg of candesartan cilexetil, the pressor
effect was inhibited by approximately 90% at peak with approximately 50%
inhibition persisting for 24 hours.
Plasma concentrations of
angiotensin I and angiotensin II, and plasma renin activity (PRA), increased in
a dose-dependent manner after single and repeated administration of candesartan
cilexetil to healthy subjects, hypertensive, and heart failure patients. ACE
activity was not altered in healthy subjects after repeated candesartan
cilexetil administration. The once-daily administration of up to 16 mg of
candesartan cilexetil to healthy subjects did not influence plasma aldosterone
concentrations, but a decrease in the plasma concentration of aldosterone was
observed when 32 mg of candesartan cilexetil was administered to hypertensive
patients. In spite of the effect of candesartan cilexetil on aldosterone
secretion, very little effect on serum potassium was observed.
Hypertension
Adults
In multiple-dose studies with
hypertensive patients, there were no clinically significant changes in
metabolic function, including serum levels of total cholesterol, triglycerides,
glucose, or uric acid. In a 12-week study of 161 patients with
non-insulin-dependent (type 2) diabetes mellitus and hypertension, there was no
change in the level of HbA1c.
Heart Failure
In heart failure patients,
candesartan ≥ 8 mg resulted in decreases in systemic vascular resistance
and pulmonary capillary wedge pressure.
Pharmacokinetics
Distribution
The volume of distribution of
candesartan is 0.13 L/kg. Candesartan is highly bound to plasma proteins
( > 99%) and does not penetrate red blood cells. The protein binding is
constant at candesartan plasma concentrations well above the range achieved
with recommended doses. In rats, it has been demonstrated that candesartan
crosses the blood-brain barrier poorly, if at all. It has also been
demonstrated in rats that candesartan passes across the placental barrier and
is distributed in the fetus.
Metabolism and Excretion
Because candesartan is not
significantly metabolized by the cytochrome P450 system and at therapeutic
concentrations has no effects on P450 enzymes, interactions with drugs that
inhibit or are metabolized by those enzymes would not be expected.
Total plasma clearance of candesartan is 0.37 mL/min/kg,
with a renal clearance of 0.19 mL/min/kg. When candesartan is administered
orally, about 26% of the dose is excreted unchanged in urine. Following an oral
dose of 14C-labeled candesartan cilexetil, approximately 33% of
radioactivity is recovered in urine and approximately 67% in feces. Following
an intravenous dose of 14C-labeled candesartan, approximately 59% of
radioactivity is recovered in urine and approximately 36% in feces. Biliary
excretion contributes to the elimination of candesartan.
Adults
Candesartan cilexetil is
rapidly and completely bioactivated by ester hydrolysis during absorption from
the gastrointestinal tract to candesartan, a selective AT1 subtype angiotensin
II receptor antagonist. Candesartan is mainly excreted unchanged in urine and
feces (via bile). It undergoes minor hepatic metabolism by O-deethylation to an
inactive metabolite. The elimination half-life of candesartan is approximately
9 hours. After single and repeated administration, the pharmacokinetics of
candesartan are linear for oral doses up to 32 mg of candesartan cilexetil.
Candesartan and its inactive metabolite do not accumulate in serum upon
repeated once-daily dosing.
Following administration of
candesartan cilexetil, the absolute bioavailability of candesartan was
estimated to be 15%. After tablet ingestion, the peak serum concentration (Cmax)
is reached after 3 to 4 hours. Food with a high fat content does not affect the
bioavailability of candesartan after candesartan cilexetil administration.
Pediatrics
In children 1 to 17 years of
age, plasma levels are greater than 10–fold higher at peak (approximately 4
hours) than 24 hours after a single dose.
Children 1 to < 6 years of
age, given 0.2 mg/kg had exposure similar to adults given 8 mg.
Children > 6 years of age
had exposure similar to adults given the same dose.
The pharmacokinetics (Cmax and
AUC) were not modified by age, sex or body weight.
Candesartan cilexetil
pharmacokinetics have not been investigated in pediatric patients less than 1
year of age.
From the dose-ranging studies
of candesartan cilexetil, there was a dose related increase in plasma
candesartan concentrations.
The renin-angiotensin system
(RAS) plays a critical role in kidney development. RAS blockade has been shown
to lead to abnormal kidney development in very young mice. Children < 1 year
of age must not receive ATACAND. Administering drugs that act directly on the
renin-angiotensin system (RAS) can alter normal renal development.
Geriatric and Sex
The pharmacokinetics of
candesartan have been studied in the elderly ( ≥ 65 years) and in both
sexes. The plasma concentration of candesartan was higher in the elderly (Cmax was
approximately 50% higher, and AUC was approximately 80% higher) compared to
younger subjects administered the same dose. The pharmacokinetics of
candesartan were linear in the elderly, and candesartan and its inactive
metabolite did not accumulate in the serum of these subjects upon repeated,
once-daily administration. No initial dosage adjustment is necessary [see DOSAGE
AND ADMINISTRATION]. There is no difference in the pharmacokinetics of
candesartan between male and female subjects.
Renal Insufficiency
In hypertensive patients with
renal insufficiency, serum concentrations of candesartan were elevated. After
repeated dosing, the AUC and Cmax were approximately doubled in patients with
severe renal impairment (creatinine clearance < 30 mL/min/1.73m²)
compared to patients with normal kidney function. The pharmacokinetics of
candesartan in hypertensive patients undergoing hemodialysis are similar to
those in hypertensive patients with severe renal impairment. Candesartan cannot
be removed by hemodialysis. No initial dosage adjustment is necessary in
patients with renal insufficiency [see DOSAGE AND ADMINISTRATION].
In heart failure patients with
renal impairment, AUC0-72h was 36% and 65% higher in mild and moderate renal
impairment, respectively. Cmax was 15% and 55% higher in mild and moderate
renal impairment, respectively.
Pediatrics
ATACAND pharmacokinetics have
not been determined in children with renal insufficiency.
Hepatic Insufficiency
The pharmacokinetics of
candesartan were compared in patients with mild and moderate hepatic impairment
to matched healthy volunteers following a single oral dose of 16 mg candesartan
cilexetil. The increase in AUC for candesartan was 30% in patients with mild
hepatic impairment (Child-Pugh A) and 145% in patients with moderate hepatic
impairment (Child-Pugh B). The increase in Cmax for candesartan was 56% in
patients with mild hepatic impairment and 73% in patients with moderate hepatic
impairment. The pharmacokinetics after candesartan cilexetil administration
have not been investigated in patients with severe hepatic impairment. No
initial dosage adjustment is necessary in patients with mild hepatic
impairment. In hypertensive patients with moderate hepatic impairment,
consideration should be given to initiation of ATACAND at a lower dose [see DOSAGE
AND ADMINISTRATION].
Heart Failure
The pharmacokinetics of
candesartan were linear in patients with heart failure (NYHA class II and III)
after candesartan cilexetil doses of 4, 8, and 16 mg. After repeated dosing,
the AUC was approximately doubled in these patients compared with healthy,
younger patients. The pharmacokinetics in heart failure patients is similar to
that in healthy elderly volunteers [see DOSAGE AND ADMINISTRATION].
Clinical Studies
Hypertension
Adult
The antihypertensive effects of
ATACAND were examined in 14 placebo-controlled trials of 4-to 12-weeks
duration, primarily at daily doses of 2 to 32 mg per day in patients with
baseline diastolic blood pressures of 95 to 114 mm Hg. Most of the trials were
of candesartan cilexetil as a single agent, but it was also studied as add-on
to hydrochlorothiazide and amlodipine. These studies included a total of 2350
patients randomized to one of several doses of candesartan cilexetil and 1027
to placebo. Except for a study in diabetics, all studies showed significant
effects, generally dose related, of 2 to 32 mg on trough (24 hour) systolic and
diastolic pressures compared to placebo, with doses of 8 to 32 mg giving
effects of about 8-12/4-8 mm Hg. There were no exaggerated first-dose effects
in these patients. Most of the antihypertensive effect was seen within 2 weeks
of initial dosing and the full effect in 4 weeks. With once-daily dosing, blood
pressure effect was maintained over 24 hours, with trough to peak ratios of
blood pressure effect generally over 80%. Candesartan cilexetil had an
additional blood pressure lowering effect when added to hydrochlorothiazide.
The antihypertensive effects of
candesartan cilexetil and losartan potassium at their highest recommended doses
administered once-daily were compared in two randomized, double-blind trials.
In a total of 1268 patients with mild to moderate hypertension who were not
receiving other antihypertensive therapy, candesartan cilexetil 32 mg lowered
systolic and diastolic blood pressure by 2 to 3 mm Hg on average more than
losartan potassium 100 mg, when measured at the time of either peak or trough
effect. The antihypertensive effects of twice daily dosing of either
candesartan cilexetil or losartan potassium were not studied.
The antihypertensive effect was
similar in men and women and in patients older and younger than 65. Candesartan
was effective in reducing blood pressure regardless of race, although the
effect was somewhat less in blacks (usually a lowrenin population). This has
been generally true for angiotensin II antagonists and ACE inhibitors.
In long-term studies of up to 1
year, the antihypertensive effectiveness of candesartan cilexetil was
maintained, and there was no rebound after abrupt withdrawal.
There were no changes in the
heart rate of patients treated with candesartan cilexetil in controlled trials.
Pediatric
The antihypertensive effects of
ATACAND were evaluated in hypertensive children 1 to < 6 years old and 6 to
< 17 years of age in two randomized, double-blind multicenter, 4-week dose
ranging studies. There were 93 patients 1 to < 6 years of age, 74% of whom
had renal disease, that were randomized to receive an oral dose of candesartan
cilexetil suspension 0.05, 0.20 or 0.40 mg/kg once daily. The primary method of
analysis was slope of the change in systolic blood pressure (SBP) as a function
of dose. Since there was no placebo group, the change from baseline likely
overestimates the true magnitude of blood pressure effect. Nevertheless, SBP
and diastolic blood pressure (DBP) decreased 6.0/5.2 to 12.0/11.1 mmHg from
baseline across the three doses of candesartan.
In children 6 to < 17 years,
240 patients were randomized to receive either placebo or low, medium, or high
doses of ATACAND in a ratio of 1: 2: 2: 2. For children who weighed < 50 kg
the doses of ATACAND were 2, 8, or 16 mg once daily. For those > 50 kg the
ATACAND doses were 4, 16 or 32 mg once daily. Those enrolled were 47% Black and
29% were female; mean age +/-SD was 12.9 +/-2.6 years.
The placebo subtracted effect
at trough for sitting systolic blood pressure/sitting diastolic blood pressure
for the different doses were from 4.9/3.0 to 7.5/6.2 mmHg.
In children 6 to < 17 years
there was a trend for a lesser blood pressure effect for Blacks compared to
other patients. There were too few individuals in the age group of 1 -6 years
old to determine whether Blacks respond differently than other patients to
ATACAND.
Heart Failure
Candesartan was studied in two
heart failure outcome studies: 1. The Candesartan in Heart failure: Assessment
of Reduction in Mortality and morbidity trial in patients intolerant of ACE
inhibitors (CHARM–Alternative), 2. CHARM– Added in patients already receiving
ACE inhibitors. Both studies were international double-blind,
placebo-controlled trials in patients with NYHA class II -IV heart failure and
LVEF ≤ 40%. In both trials, patients were randomized to placebo or ATACAND
(initially 4-8 mg once daily, titrated as tolerated to 32 mg once daily) and
followed for up to 4 years. Patients with serum creatinine > 3 mg/dL, serum
potassium > 5.5 mEq/L, symptomatic hypotension or known bilateral renal
artery stenosis were excluded. The primary end point in both trials was time to
either cardiovascular death or hospitalization for heart failure.
CHARM–Alternative included 2028
subjects not receiving an ACE inhibitor due to intolerance. The mean age was 67
years and 32% were female, 48% were NYHA II, 49% were NYHA III, 4% were NYHA
IV, and the mean ejection fraction was 30%. Sixty-two percent had a history of
myocardial infarction, 50% had a history of hypertension, and 27% had diabetes.
Concomitant drugs at baseline were diuretics (85%), digoxin (46%),
beta-blockers (55%), and spironolactone (24%). The mean daily dose of ATACAND
was approximately 23 mg and 59% of subjects on treatment received 32 mg once
daily.
After a median follow-up of 34
months, there was a 23% reduction in the risk of cardiovascular death or heart
failure hospitalization on ATACAND (p < 0.001), with both components
contributing to the overall effect (Table 1).
Table 1: CHARM—Alternative: Primary Endpoint and its
Components
Endpoint (time to first event) |
ATACAND
(n= 1013) |
Placebo
(n=1015) |
Hazard Ratio (95% CI) |
p-value (logrank) |
CV death or heart failure hospitalization |
334 |
406 |
0.77
(0.67-0.89) |
< 0.001 |
CV death |
219 |
252 |
0.85
(0.71-1.02) |
0.072 |
Heart failure hospitalization |
207 |
286 |
0.68
(0.57-0.81) |
< 0.001 |
In CHARM–Added, 2548 subjects
receiving an ACE inhibitor were randomized to ATACAND or placebo. The specific
ACE inhibitor and dose were at the discretion of the investigators, who were
encouraged to titrate patients to doses known to be effective in clinical
outcome trials, subject to patient tolerability. Forced titration to maximum
tolerated doses of ACE inhibitor was not required.
The mean age was 64 years and
21% were female, 24% were NYHA II, 73% were NYHA III, 3% were NYHA IV, and the
mean ejection fraction was 28%. Fifty-six percent had a history of myocardial
infarction, 48% had a history of hypertension, and 30% had diabetes.
Concomitant drugs at baseline in addition to ACE inhibitors were diuretics
(90%), digoxin (58%), beta-blockers (55%), and spironolactone (17%). The mean
daily dose of ATACAND was approximately 24 mg and 61% of subjects on treatment
received 32 mg once daily.
After a median follow-up of 41
months, there was a 15% reduction in the risk of cardiovascular death or heart
failure hospitalization on ATACAND (p=0.011), with both components contributing
to the overall effect (Table 2). There was no evident relationship between dose
of ACE inhibitor and the benefit of ATACAND.
Table 2: CHARM—Added:
Primary Endpoint and its Components
Endpoint (time to first event) |
ATACAND
(n=1276) |
Placebo
(n=1272) |
Hazard Ratio (95% CI) |
p-value (logrank) |
CV death or heart failure hospitalization |
483 |
538 |
0.85
(0.75-0.96) |
0.011 |
CV death |
302 |
347 |
0.84
(0.72-0.98) |
0.029 |
Heart failure hospitalization |
309 |
356 |
0.83
(0.71-0.96) |
0.014 |
In these two studies, the
benefit of ATACAND in reducing the risk of CV death or heart failure
hospitalization (18% p < 0.001) was evident in major subgroups (see Figure),
and in patients on other combinations of cardiovascular and heart failure
treatments, including ACE inhibitors and beta-blockers.
Figure: CV Death or Heart
Failure Hospitalization in Subgroups – LV Systolic Dysfunction Trials