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. 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
For an equivalent dose, PREXXARTAN has 86% higher peak
concentration (Cmax) and 25% higher area under the plasma concentration over
time curve (AUC) for valsartan compared to Diovan. AUC and Cmax of valsartan
increase approximately linearly with increasing dose over the clinical dosing
range. Valsartan does not accumulate appreciably in plasma following repeated
administration.
Absorption
PREXXARTAN Cmax is achieved 0.7 to 3.7 hours after
dosing.
Effect Of Food
High-fat, high-calorie meal decreased the AUC of
PREXXARTAN by about 8% and Cmax by about 44%.
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.
Elimination
Following intravenous administration, plasma clearance of
valsartan is about 2 L/h. Renal clearance of valsartan is 0.62 L/h (about 30%
of total body clearance). Valsartan shows bi-exponential decay kinetics
following intravenous administration, with an average elimination half-life of
about 6 hours.
Metabolism
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-4hydroxy valsartan. Valsartan does not inhibit CYP
450 isozymes at clinically relevant concentrations. CYP 450 mediated drug
interaction between valsartan and co-administered drugs are unlikely because of
the low extent of metabolism.
Excretion
When administered as an oral solution, 83% of the dose is
recovered in feces and about 13% is recovered in urine. The recovery is mainly
as unchanged drug, with only about 20% of dose recovered as metabolites.
Specific Populations
Geriatric Patients
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.
Pediatric Patients
In a study of pediatric hypertensive patients (n=26, 1 to
16 years of age) given single doses of a suspension of valsartan (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.
Male And Female Patients
Pharmacokinetics of valsartan does not differ
significantly between males and females.
Heart Failure Patients
The average time to peak concentration and elimination
half-life of valsartan in heart failure patients are similar to those 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.
Patients With Renal Impairment
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, monitor
closely [see DOSAGE AND ADMINISTRATION].
Patients With Hepatic Impairment
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. Monitor
closely patients with liver disease [see DOSAGE AND ADMINISTRATION].
Drug Interactions
No clinically significant pharmacokinetic interactions
were observed when valsartan was coadministered with nebivolol, amlodipine,
atenolol, cimetidine, digoxin, furosemide, glyburide, hydrochlorothiazide, or
indomethacin.
Co-administration of valsartan and warfarin did not
change the pharmacokinetics of valsartan or the time-course of the
anticoagulant properties of warfarin.
Transporters
The results from an in vitro study with human liver
tissue indicate that valsartan is a substrate of the hepatic uptake transporter
OATP1B1 and the hepatic efflux transporter MRP2. Coadministration of inhibitors
of the uptake transporter (rifampin, cyclosporine) or efflux transporter
(ritonavir) may increase the systemic exposure to valsartan.
Animal Toxicology And/Or Pharmacology
Daily oral dosing of neonatal/juvenile rats with
valsartan at doses as low as 1 mg/kg/day (about 10% of the maximum recommended
pediatric dose on a mg/m² basis) from postnatal day 7 to postnatal day 70 produced
persistent, irreversible kidney damage. These kidney effects in neonatal rats
represent expected exaggerated pharmacological effects that are observed if
rats are treated during the first 13 days of life.
Clinical Studies
Hypertension
Studies evaluating the antihypertensive effects of
valsartan were conducted with a formulation that is not therapeutically
equivalent to PREXXARTAN [see CLINICAL PHARMACOLOGY].
Adult Hypertension
The antihypertensive effects of valsartan were
demonstrated principally in 7 placebo-controlled, 4- to 12-week trials (1 in
patients over 65 years) of dosages from 10 to 320 mg/day in patients with
baseline diastolic blood pressures of 95-115 mmHg. 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 2 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 valsartan 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 to 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 are no trials of valsartan demonstrating reductions
in cardiovascular risk in patients with hypertension, but at least one
pharmacologically similar drug has demonstrated such benefits.
There was essentially no change in heart rate in
valsartan-treated patients in controlled trials.
Pediatric Hypertension
The antihypertensive effects of valsartan 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 mmHg 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 mmHg 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. The VAL-HeFT study was conducted with a
formulation of valsartan that is not therapeutically equivalent to PREXXARTAN [see
CLINICAL PHARMACOLOGY]. 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 following table.
|
Placebo
(N=2,499) |
Valsartan
(N=2,511) |
Hazard Ratio (95% CI*) |
Nominal p-value |
All-cause mortality |
484
(19.4%) |
495
(19.7%) |
1.02
(0.90-1.15) |
0.8 |
HF morbidity |
801
(32.1%) |
723
(28.8%) |
0.87
(0.79-0.97) |
0.009 |
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). The VALIANT
study was conducted with a formulation of valsartan that is not therapeutically
equivalent to PREXXARTAN [see CLINICAL PHARMACOLOGY]. Patients were
randomized within 12 hours to 10 days after the onset of myocardial infarction
symptoms to one of three treatment groups: valsartan (titrated from 20 or 40 mg
twice dailyto 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 from 20 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 2 years. The mean daily dose of
Valsartan 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 following
table.
|
Valsartan (N=4,909) vs. Captopril (N=4,909) |
Valsartan + Captopril (N=4,885) vs. 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% to 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 to 1.11, a difference
of about 9% to 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.