Mechanism of Action
Eprosartan: Angiotensin II (formed from angiotensin I in a reaction
catalyzed by angiotensin-converting enzyme [kininase II]), a potent vasoconstrictor,
is the principal pressor agent of the renin-angiotensin system. Angiotensin
II also stimulates aldosterone synthesis and secretion by the adrenal cortex,
cardiac contraction, renal resorption of sodium, activity of the sympathetic
nervous system, and smooth muscle cell growth. Eprosartan blocks the vasoconstrictor
and aldosterone-secreting effects of angiotensin II by selectively blocking
the binding of angiotensin II to the AT1 receptor found in many tissues
(e.g., vascular smooth muscle, adrenal gland). There is also an AT2
receptor found in many tissues but it is not known to be associated with cardiovascular
homeostasis. Eprosartan does not exhibit any partial agonist activity at the
AT1 receptor. Its affinity for the AT1 receptor is 1,000
times greater than for the AT2 receptor. In vitro binding
studies indicate that eprosartan is a reversible, competitive inhibitor of the
AT1 receptor. Blockade of the AT1 receptor removes the negative feedback of angiotensin II on renin secretion, but the resulting increased
plasma renin activity and circulating angiotensin II do not overcome the effect
of eprosartan on blood pressure. TEVETEN® HCT does not inhibit kininase
II, the enzyme that converts angiotensin I to angiotensin II and degrades bradykinin;
whether this has clinical relevance is not known. It does not bind to or block
other hormone receptors or ion channels known to be important in cardiovascular
regulation.
Hydrochlorothiazide: Hydrochlorothiazide 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 hydrochlorothiazide 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 an angiotensin II receptor antagonist tends to reverse the potassium loss
associated with these diuretics. The mechanism of the antihypertensive effect
of thiazides is unknown.
Pharmacokinetics
General
Eprosartan: Absolute bioavailability following a single 300-mg
oral dose of eprosartan is approximately 13%. Eprosartan plasma concentrations
peak at 1 to 2 hours after an oral dose in the fasted state. Administering eprosartan
with food delays absorption, and causes variable changes ( < 25%) in Cmax and
AUC values which do not appear clinically important. Plasma concentrations of
eprosartan increase in a slightly less than dose-proportional manner over the
100 mg to 800 mg dose range. The mean terminal elimination half-life of eprosartan
following multiple oral doses of 600 mg was approximately 20 hours. Eprosartan
does not significantly accumulate with chronic use.
Hydrochlorothiazide: When hydrochlorothiazide plasma levels have
been followed for at least 24 hours, the plasma half-life has been observed
to vary between 5.6 and 14.8 hours.
Metabolism and Excretion
Eprosartan: Eprosartan is eliminated by biliary and renal excretion,
primarily as unchanged compound. Less than 2% of an oral dose is excreted in
the urine as a glucuronide. There are no active metabolites following oral and
intravenous dosing with [14C] eprosartan in human subjects. Eprosartan
was the only drug-related compound found in the plasma and feces. Following
intravenous [14C] eprosartan, about 61% of the material is recovered
in the feces and about 37% in the urine. Following an oral dose of [14C]
eprosartan, about 90% is recovered in the feces and about 7% in the urine. Approximately
20% of the radioactivity excreted in the urine was an acyl glucuronide of eprosartan
with the remaining 80% being unchanged eprosartan. Eprosartan is not metabolized
by cytochrome P450 enzymes.
Hydrochlorothiazide: Hydrochlorothiazide is not metabolized but
is eliminated rapidly by the kidney. At least 61% of the oral dose is eliminated
unchanged within 24 hours.
Distribution
Eprosartan: Plasma protein binding of eprosartan is high (approximately
98%) and constant over the concentration range achieved with therapeutic doses.
The pooled population pharmacokinetic analysis from two Phase 3 trials of 299
men and 172 women with mild to moderate hypertension (aged 20 to 93 years) showed
that eprosartan exhibited a population mean oral clearance (CL/F) for an average
60-year-old patient of 48.5 L/hr. The population mean steady-state volume of
distribution (Vss/F) was 308 L. Eprosartan pharmacokinetics were not influenced
by weight, race, gender or severity of hypertension at baseline. Oral clearance
was shown to be a linear function of age with CL/F decreasing 0.62 L/hr for
every year increase.
Hydrochlorothiazide: Hydrochlorothiazide crosses the placental
but not the blood-brain barrier and it is excreted in breast milk.
Special Populations
Pediatric:Eprosartan pharmacokinetics have not been investigated
in patients younger than 18 years of age.
Geriatric:Following single oral dose administration of eprosartan
to healthy elderly men, (aged 68 to 78 years), AUC, Cmax, and Tmax eprosartan
values increased, on average, by approximately twofold, compared to healthy
young men (aged 20 to 38 years) who received the same dose. The extent of plasma
protein binding is not influenced by age.
Gender:There was no difference in the pharmacokinetics and plasma
protein binding between men and women following single oral dose administration
of eprosartan.
Race:A pooled population pharmacokinetic analysis of 442 Caucasian
and 29 non-Caucasian hypertensive patients showed that oral clearance and steady-state
volume of distribution were not influenced by race.
Renal Insufficiency: Following administration of 600 mg once
daily, there was a 70-90% increase in AUC, and a 30-50% increase in Cmax in
moderate or severe renal impairment. The unbound eprosartan fractions increased
by 35% and 59% in patients with moderate and severe renal impairment, respectively.
No initial dosing adjustment is generally necessary in patients with moderate
or severe renal impairment, with maximum dose not exceeding 600 mg daily. Eprosartan
was poorly removed by hemodialysis (CLHD < 1L/hr) (see DOSAGE AND ADMINISTRATION).
Hepatic Insufficiency: Eprosartan AUC (but not Cmax) values increased,
on average, by approximately 40% in men with decreased hepatic function compared
to healthy men after a single 100 mg oral dose of eprosartan. The extent of
eprosartan plasma protein binding was not influenced by hepatic dysfunction.
No dosage adjustment is necessary for patients with hepatic impairment.
Drug Interactions
Eprosartan: Concomitant administration of eprosartan with digoxin
had no effect on a single oral-dose digoxin pharmacokinetics. Concomitant administration
of eprosartan and warfarin had no effect on steady-state prothrombin time ratios
(INR) in healthy volunteers. Concomitant administration of eprosartan and glyburide
in diabetic patients did not affect 24-hour plasma glucose profiles. Eprosartan
pharmacokinetics were not affected by concomitant administration of ranitidine.
Eprosartan did not inhibit human cytochrome P450 enzymes CYP1A, 2A6, 2C9/8,
2C19, 2D6, 2E, and 3A in vitro. Eprosartan steady-state plasma concentrations
were not affected by concomitant administration of ketoconazole or fluconazole,
potent inhibitors of CYP3A and 2C9, respectively.
Eprosartan-Hydrochlorothiazide:There is no pharmacokinetic
interaction between 600 mg eprosartan and 12.5 mg hydrochlorothiazide.
Pharmacodynamics and Clinical Effects
Eprosartan: Eprosartan inhibits the pharmacologic effects of
angiotensin II infusions in healthy adult men. Single oral doses of eprosartan
from 10 mg to 400 mg have been shown to inhibit the vasopressor, renal vasoconstrictive
and aldosterone secretory effects of infused angiotensin II with complete inhibition
evident at doses of 350 mg and above. Eprosartan inhibits the pressor effects
of angiotensin II infusions. A single oral dose of 350 mg of eprosartan inhibits
pressor effects by approximately 100% at peak, with approximately 30% inhibition
persisting for 24 hours. The absence of angiotensin II AT1 agonist
activity has been demonstrated in healthy adult men. In hypertensive patients
treated chronically with eprosartan, there was a twofold rise in angiotensin
II plasma concentration and a twofold rise in plasma renin activity, while plasma
aldosterone levels remained unchanged. Serum potassium levels also remained
unchanged in these patients. Achievement of maximal blood pressure response
to a given dose in most patients may take2 to 3 weeks of treatment. Onset of
blood pressure reduction is seen within 1 to 2 hours of dosing with few instances
of orthostatic hypotension. Blood pressure control is maintained with once-
or twice-daily dosing over a 24-hour period. Discontinuing treatment with eprosartan
does not lead to a rapid rebound increase in blood pressure. There was no change
in mean heart rate in patients treated with eprosartan in controlled clinical
trials. Eprosartan increases mean effective renal plasma flow (ERPF) in salt-replete
and salt-restricted normal subjects. A dose-related increase in ERPF of 25%
to 30% occurred in salt-restricted normal subjects, with the effect plateauing
between 200 mg and 400 mg doses. There was no change in ERPF in hypertensive
patients and patients with renal insufficiency on normal salt diets. Eprosartan
did not reduce glomerular filtration rate in patients with renal insufficiency
or in patients with hypertension, after 7 days and 28 days of dosing, respectively.
In hypertensive patients and patients with chronic renal insufficiency, eprosartan
did not change fractional excretion of sodium and potassium. Eprosartan (1200
mg once daily for 7 days or 300 mg twice daily for 28 days) had no effect on
the excretion of uric acid in healthy men, patients with essential hypertension
or those with varying degrees of renal insufficiency. There were no effects
on mean levels of fasting triglycerides, total cholesterol, HDL cholesterol,
LDL cholesterol or fasting glucose.
Clinical Trials
Eprosartan Mesylate: The safety and efficacy of TEVETEN®
(eprosartan mesylate) has been evaluated in controlled clinical trials worldwide
that enrolled predominantly hypertensive patients with sitting DBP ranging from
95 mmHg to =115 mmHg. There is also some experience with use of eprosartan together
with other antihypertensive drugs in more severe hypertension. The antihypertensive
effects of TEVETEN® were demonstrated principally in five placebo-controlled
trials (4 to 13 weeks' duration) including dosages of 400 mg to 1200 mg given
once daily (two studies), 25 mg to 400 mg twice daily (two studies), and one
study comparing total daily doses of 400 mg to 800 mg given once daily or twice
daily. The five studies included 1,111 patients randomized to eprosartan and
395 patients randomized to placebo. The studies showed dose-related anti-hypertensive
responses. At study endpoint, patients treated with TEVETEN® at doses of
600 mg to 1200 mg given once daily experienced significant decreases in sitting
systolic and diastolic blood pressure at trough, with differences from placebo
of approximately 5-10/3-6 mmHg. Limited experience is available with the dose
of 1200 mg administered once daily. In a direct comparison of 200 mg to 400
mg b.i.d. with 400 mg to 800 mg q.d. of TEVETEN® , effects at trough were
similar. Patients treated with TEVETEN® at doses of 200 mg to 400 mg given
twice daily experienced significant decreases in sitting systolic and diastolic
blood pressure at trough, with differences from placebo of approximately 7-10/4-6
mmHg. Peak (1 to 3 hours) effects were uniformly, but moderately, larger than
trough effects with b.i.d. dosing, with the trough-to-peak ratio for diastolic
blood pressure 65% to 80%. In the once-daily dose-response study, trough-to-peak
responses of =50% were observed at some doses (including 1200 mg), suggesting
attenuation of effect at the end of the dosing interval. The antihypertensive
effect of TEVETEN® was similar in men and women, but was somewhat smaller
in patients over 65. There were too few black subjects to determine whether
their response was similar to Caucasians. In general, blacks (usually a low
renin population) have had smaller responses to ACE inhibitors and angiotensin
II inhibitors than Caucasian populations. Angiotensin-converting enzyme (ACE)
inhibitor-induced cough (a dry, persistent cough) can lead to discontinuation
of ACE inhibitor therapy. In one study, patients who had previously coughed
while taking an ACE inhibitor were treated with eprosartan, an ACE inhibitor
(enalapril) or placebo for six weeks. The incidence of dry, persistent cough
was 2.2% on eprosartan, 4.4% on placebo, and 20.5% on the ACE inhibitor; p=0.008
for the comparison of eprosartan with enalapril. In a second study comparing
the incidence of cough in 259patients treated with eprosartan to 261 patients
treated with the ACE inhibitor enalapril, the incidence of dry, persistent cough
in eprosartan-treated patients (1.5%) was significantly lower (p=0.018)
than that observed in patients treated with the ACE inhibitor (5.4%). In addition,
analysis of overall data from six double-blind clinical trials involving 1,554
patients showed an incidence of spontaneously reported cough in patients treated
with eprosartan of 3.5%, similar to placebo (2.6%).
Hydrochlorothiazide: After oral administration of hydrochlorothiazide,
diuresis begins within 2 hours, peaks in about 4 hours, and lasts about 6 to
12 hours.
Eprosartan Mesylate - Hydrochlorothiazide: Four adequate and
well-controlled studies were conducted to assess the antihypertensive effectiveness
of TEVETEN® HCT (eprosartan mesylate/hydrochlorothiazide) in 1457 patients
with mild-to-moderate essential hypertension. In a 2x2 factorial study with
112-119 hypertensive patients per arm, the mean baseline- and placebo-subtracted
reductions in blood pressure at 8 weeks were 3.6/2.1 mmHg on eprosartan 600
mg, 5.6/1.9 mmHg on hydrochlorothiazide 12.5 mg, and 10.0/5.0 mmHg on the combination.
Last updated on RxList: 7/16/2008