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. Diovan (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 II 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
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.
In multiple-dose studies in hypertensive patients, valsartan
had no notable effects on total cholesterol, fasting triglycerides, fasting
serum glucose, or uric acid.
Pharmacokinetics
Valsartan peak plasma concentration is reached 2 to 4 hours after dosing. Valsartan
shows bi-exponential decay kinetics following intravenous administration, with
an average elimination half-life of about 6 hours. Absolute bioavailability
for Diovan is about 25% (range 10%-35%). The bioavailability of the suspension
(see DOSAGE AND ADMINISTRATION; Pediatric
Hypertension) is 1.6 times greater than with the tablet. With the tablet,
food decreases the exposure (as measured by AUC) to valsartan by about 40% and
peak plasma concentration (Cmax) by about 50%. AUC and Cmax values of valsartan
increase approximately linearly with increasing dose over the clinical dosing
range. Valsartan does not accumulate appreciably in plasma following repeated
administration.
Metabolism and Elimination
Valsartan, when administered as an oral solution, is
primarily recovered in feces (about 83% of dose) and urine (about 13% of dose).
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 isozymes.
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).
Distribution
The steady state volume of distribution of valsartan after
intravenous administration is small (17 L), indicating that valsartan does not
distribute into tissues extensively. Valsartan is highly bound to serum
proteins (95%), mainly serum albumin.
Special Populations
Pediatric: In a study of pediatric
hypertensive patients (n=26, 1-16 years of age) given single doses of a
suspension of Diovan (mean: 0.9 to 2 mg/kg), the clearance (L/h/kg) of
valsartan for children was similar to that of adults receiving the same
formulation.
Geriatric: 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 [see DOSAGE AND
ADMINISTRATION].
Gender: Pharmacokinetics of valsartan does not
differ significantly between males and females.
Heart Failure: The average time to peak
concentration and elimination half-life of valsartan in heart failure patients
are similar to that observed in healthy volunteers. AUC and Cmax values of
valsartan increase linearly and are almost proportional with increasing dose
over the clinical dosing range (40 to 160 mg twice a day). The average
accumulation factor is about 1.7. The apparent clearance of valsartan following
oral administration is approximately 4.5 L/h. Age does not affect the apparent
clearance in heart failure patients.
Renal Insufficiency: 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 [see DOSAGE AND ADMINISTRATION].
Hepatic Insufficiency: 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 [see DOSAGE AND ADMINISTRATION].
Clinical Studies
Hypertension
Adult Hypertension
The antihypertensive effects of Diovan (valsartan) were
demonstrated principally in 7 placebo-controlled, 4- to 12-week trials (one in
patients over 65) of dosages from 10 to 320 mg/day in patients with baseline
diastolic blood pressures of 95-115. The studies allowed comparison of
once-daily and twice-daily regimens of 160 mg/day; comparison of peak and
trough effects; comparison (in pooled data) of response by gender, age, and
race; and evaluation of incremental effects of hydrochlorothiazide.
Administration of valsartan to patients with essential
hypertension results in a significant reduction of sitting, supine, and
standing systolic and diastolic blood pressure, usually with little or no
orthostatic change.
In most patients, after administration of a single oral
dose, onset of antihypertensive activity occurs at approximately 2 hours, and
maximum reduction of blood pressure is achieved within 6 hours. The
antihypertensive effect persists for 24 hours after dosing, but there is a
decrease from peak effect at lower doses (40 mg) presumably reflecting loss of
inhibition of angiotensin II. At higher doses, however (160 mg), there is
little difference in peak and trough effect. During repeated dosing, the
reduction in blood pressure with any dose is substantially present within 2
weeks, and maximal reduction is generally attained after 4 weeks. In long-term
follow-up studies (without placebo control), the effect of valsartan appeared
to be maintained for up to two years. The antihypertensive effect is
independent of age, gender or race. The latter finding regarding race is based
on pooled data and should be viewed with caution, because antihypertensive
drugs that affect the renin-angiotensin system (that is, ACE inhibitors and
angiotensin-II blockers) have generally been found to be less effective in
low-renin hypertensives (frequently blacks) than in high-renin hypertensives
(frequently whites). In pooled, randomized, controlled trials of Diovan that
included a total of 140 blacks and 830 whites, valsartan and an ACE-inhibitor
control were generally at least as effective in blacks as whites. The
explanation for this difference from previous findings is unclear.
Abrupt withdrawal of valsartan has not been associated with
a rapid increase in blood pressure.
The blood pressure lowering effect of valsartan and
thiazide-type diuretics are approximately additive.
The 7 studies of valsartan monotherapy included over 2,000
patients randomized to various doses of valsartan and about 800 patients
randomized to placebo. Doses below 80 mg were not consistently distinguished
from those of placebo at trough, but doses of 80, 160 and 320 mg produced
dose-related decreases in systolic and diastolic blood pressure, with the
difference from placebo of approximately 6-9/3-5 mmHg at 80-160 mg and 9/6 mmHg
at 320 mg. In a controlled trial the addition of HCTZ to valsartan 80 mg
resulted in additional lowering of systolic and diastolic blood pressure by
approximately 6/3 and 12/5 mmHg for 12.5 and 25 mg of HCTZ, respectively,
compared to valsartan 80 mg alone.
Patients with an inadequate response to 80 mg once daily
were titrated to either 160 mg once daily or 80 mg twice daily, which resulted
in a comparable response in both groups.
In controlled trials, the antihypertensive effect of
once-daily valsartan 80 mg was similar to that of once-daily enalapril 20 mg or
once-daily lisinopril 10 mg.
There was essentially no change in heart rate in
valsartan-treated patients in controlled trials.
Pediatric Hypertension
The antihypertensive effects of Diovan were evaluated in two
randomized, double-blind clinical studies.
In a clinical study involving 261 hypertensive pediatric
patients 6 to 16 years of age, patients who weighed < 35 kg received 10, 40
or 80 mg of valsartan daily (low, medium and high doses), and patients who
weighed ≥ 35 kg received 20, 80, and 160 mg of valsartan daily (low,
medium and high doses). Renal and urinary disorders, and essential hypertension
with or without obesity were the most common underlying causes of hypertension
in children enrolled in this study. At the end of 2 weeks, valsartan reduced
both systolic and diastolic blood pressure in a dose-dependent manner. Overall,
the three dose levels of valsartan (low, medium and high) significantly reduced
systolic blood pressure by -8, -10, -12 mm Hg from the baseline, respectively.
Patients were re-randomized to either continue receiving the same dose of
valsartan or were switched to placebo. In patients who continued to receive the
medium and high doses of valsartan, systolic blood pressure at trough was -4
and -7 mm Hg lower than patients who received the placebo treatment. In
patients receiving the low dose of valsartan, systolic blood pressure at trough
was similar to that of patients who received the placebo treatment. Overall,
the dose-dependent antihypertensive effect of valsartan was consistent across
all the demographic subgroups.
In a clinical study involving 90 hypertensive pediatric
patients 1 to 5 years of age with a similar study design, there was some
evidence of effectiveness, but safety findings for which a relationship to
treatment could not be excluded mitigate against recommending use in this age
group. [see ADVERSE REACTIONS].
Heart Failure
The Valsartan Heart Failure Trial (Val-HeFT) was a
multinational, double-blind study in which 5,010 patients with NYHA class II
(62%) to IV (2%) heart failure and LVEF < 40%, on baseline therapy chosen by
their physicians, were randomized to placebo or valsartan (titrated from 40 mg
twice daily to the highest tolerated dose or 160 mg twice daily) and followed
for a mean of about 2 years. Although Val-HeFT's primary goal was to examine
the effect of valsartan when added to an ACE inhibitor, about 7% were not
receiving an ACE inhibitor. Other background therapy included diuretics (86%),
digoxin (67%), and beta-blockers (36%). The population studied was 80% male,
46% 65 years or older and 89% Caucasian. At the end of the trial, patients in
the valsartan group had a blood pressure that was 4 mmHg systolic and 2 mmHg
diastolic lower than the placebo group. There were two primary end points, both
assessed as time to first event: all-cause mortality and heart failure
morbidity, the latter defined as all-cause mortality, sudden death with
resuscitation, hospitalization for heart failure, and the need for intravenous
inotropic or vasodilatory drugs for at least 4 hours. These results are
summarized in the table below.
| |
Placebo
(N=2,499) |
Valsartan
(N=2,511) |
Hazard Ratio
(95% CI*) |
Nominal
p-value |
| All-cause mortality |
484 |
495 |
1.02 |
0.8 |
| (19.4%) |
(19.7%) |
(0.90-1.15) |
|
| HF morbidity |
801 |
723 |
0.87 |
0.009 |
| (32.1%) |
(28.8%) |
(0.79-0.97) |
|
| * CI = Confidence Interval |
Although the overall morbidity result favored valsartan, this result was largely
driven by the 7% of patients not receiving an ACE inhibitor, as shown in the
following table.
| |
Without ACE Inhibitor |
With ACE Inhibitor |
Placebo
(N=181) |
Valsartan
(N=185) |
Placebo
(N=2,318) |
Valsartan
(N=2,326) |
| Events (%) |
77 (42.5%) |
46 (24.9%) |
724 (31.2%) |
677 (29.1%) |
| Hazard ratio (95% CI) |
0.51 (0.35, |
0.73) |
0.92 (0.82, |
1.02) |
| p-value |
0.0002 |
0.0965 |
The modest favorable trend in the group receiving an ACE
inhibitor was largely driven by the patients receiving less than the
recommended dose of ACE inhibitor. Thus, there is little evidence of further
clinical benefit when valsartan is added to an adequate dose of ACE inhibitor.
Secondary end points in the subgroup not receiving ACE
inhibitors were as follows.
| |
Placebo
(N=181) |
Valsartan
(N=185) |
Hazard Ratio
(95% CI) |
| Components of HF morbidity |
| All-cause mortality |
49 (27.1%) |
32 (17.3%) |
0.59 (0.37, 0.91) |
| Sudden death with resuscitation |
2 (1.1%) |
1 (0.5%) |
0.47 (0.04, 5.20) |
| CHF therapy |
1 (0.6%) |
0 (0.0%) |
– |
| CHF hospitalization |
48 (26.5%) |
24 (13.0%) |
0.43 (0.27, 0.71) |
| Cardiovascular mortality |
40 (22.1%) |
29 (15.7%) |
0.65 (0.40, 1.05) |
| Non-fatal morbidity |
49 (27.1%) |
24 (13.0%) |
0.42 (0.26, 0.69) |
In patients not receiving an ACE inhibitor,
valsartan-treated patients had an increase in ejection fraction and reduction
in left ventricular internal diastolic diameter (LVIDD).
Effects were generally consistent across subgroups defined
by age and gender for the population of patients not receiving an ACE
inhibitor. The number of black patients was small and does not permit a
meaningful assessment in this subset of patients.
Post-Myocardial Infarction
The VALsartan In Acute myocardial iNfarcTion trial (VALIANT)
was a randomized, controlled, multinational, double-blind study in 14,703
patients with acute myocardial infarction and either heart failure (signs,
symptoms or radiological evidence) or left ventricular systolic dysfunction
(ejection fraction ≤ 40% by radionuclide ventriculography or ≤ 35% by
echocardiography or ventricular contrast angiography). Patients were randomized
within 12 hours to 10 days after the onset of myocardial infarction symptoms to
one of three treatment groups: valsartan (titrated from²0 or 40 mg twice daily
to the highest tolerated dose up to a maximum of 160 mg twice daily), the ACE
inhibitor, captopril (titrated from 6.25 mg three times daily to the highest
tolerated dose up to a maximum of 50 mg three times daily), or the combination
of valsartan plus captopril. In the combination group, the dose of valsartan
was titrated from²0 mg twice daily to the highest tolerated dose up to a
maximum of 80 mg twice daily; the dose of captopril was the same as for
monotherapy. The population studied was 69% male, 94% Caucasian, and 53% were
65 years of age or older. Baseline therapy included aspirin (91%),
beta-blockers (70%), ACE inhibitors (40%), thrombolytics (35%) and statins
(34%). The mean treatment duration was two years. The mean daily dose of Diovan
in the monotherapy group was 217 mg.
The primary endpoint was time to all-cause mortality.
Secondary endpoints included (1) time to cardiovascular (CV) mortality, and (2)
time to the first event of cardiovascular mortality, reinfarction, or
hospitalization for heart failure. The results are summarized in the table
below:
| |
Valsartan (N=4,909)
vs.
Captopril (N=4,909) |
Valsartan +(N=4,885)
vs.
Captopril Captopril (N=4,909) |
No. of Deaths
Valsartan/Captopril |
Hazard Ratio CI |
p-value |
No. of Deaths
Comb/Captopril |
Hazard Ratio
CI |
p-value |
| All-cause mortality |
979 (19.9%)/ 958 (19.5%) |
1.001 (0.902, 1.111) |
0.98 |
941 (19.3%)/ 958 (19.5%) |
0.984 (0.886, 1.093) |
0.73 |
| CV mortality |
827 (16.8%)/ 830 (16.9%) |
0.976 (0.875, 1.090) |
|
|
|
|
| CV mortality, hospitalization for HF, and recurrent non-fatal MI |
1,529 (31.1%)/ 1,567 (31.9%) |
0.955 (0.881, 1.035) |
|
|
|
|
There was no difference in overall mortality among the three
treatment groups. There was thus no evidence that combining the ACE inhibitor
captopril and the angiotensin II blocker valsartan was of value.
The data were assessed to see whether the effectiveness of
valsartan could be demonstrated by showing in a non-inferiority analysis that
it preserved a fraction of the effect of captopril, a drug with a demonstrated
survival effect in this setting. A conservative estimate of the effect of
captopril (based on a pooled analysis of 3 post-infarction studies of captopril
and 2 other ACE inhibitors) was a 14-16% reduction in mortality compared to
placebo. Valsartan would be considered effective if it preserved a meaningful
fraction of that effect and unequivocally preserved some of that effect. As
shown in the table, the upper bound of the CI for the hazard ratio
(valsartan/captopril) for overall or CV mortality is 1.09-1.11, a difference of
about 9-11%, thus making it unlikely that valsartan has less than about half of
the estimated effect of captopril and clearly demonstrating an effect of
valsartan. The other secondary endpoints were consistent with this conclusion.
Effects on Mortality Amongst Subgroups in VALIANT
There were no clear differences in all-cause mortality based
on age, gender, race, or baseline therapies, as shown in the figure above.
Last updated on RxList: 7/6/2009