CLINICAL PHARMACOLOGY
Mechanism of Action
Aliskiren
Renin is secreted by the kidney
in response to decreases in blood volume and renal perfusion. Renin cleaves
angiotensinogen to form the inactive decapeptide angiotensin I (Ang I). Ang I
is converted to the active octapeptide angiotensin II (Ang II) by angiotensin-converting
enzyme (ACE) and non-ACE pathways. Ang II is a powerful vasoconstrictor and
leads to the release of catecholamines from the adrenal medulla and
prejunctional nerve endings. It also promotes aldosterone secretion and sodium
reabsorption. Together, these effects increase blood pressure. Ang II also
inhibits renin release, thus providing a negative feedback to the system. This
cycle, from renin through angiotensin to aldosterone and its associated
negative feedback loop, is known as the renin-angiotensin-aldosterone system
(RAAS). Aliskiren is a direct renin inhibitor, decreasing plasma renin activity
(PRA) and inhibiting the conversion of angiotensinogen to Ang I. Whether
aliskiren affects other RAAS components, e.g., ACE or non-ACE pathways, is not
known.
All agents that inhibit the
RAAS, including renin inhibitors, suppress the negative feedback loop, leading
to a compensatory rise in plasma renin concentration. When this rise occurs
during treatment with ACE inhibitors and ARBs, the result is increased levels
of PRA. During treatment with aliskiren, however, the effect of increased renin
levels is blocked, so that PRA, Ang I and Ang II are all reduced, whether
aliskiren is used as monotherapy or in combination with other antihypertensive
agents.
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 agents that block the
production or function of angiotensin II tends to reverse the potassium loss
associated with these diuretics.
The mechanism of action of the antihypertensive effect of
thiazides is unknown.
Pharmacodynamics
Tekturna HCT
In placebo-controlled clinical trials, PRA was decreased
with aliskiren monotherapy (ranging from 54% to 65%) and increased with
hydrochlorothiazide monotherapy (ranging from 4% to 72%). Treatment with
Tekturna HCT resulted in PRA reductions ranging from approximately 46% to 63%
in various doses despite the increase in PRA with hydrochlorothiazide
treatment. The clinical implications of the differences in effect on PRA are
not known.
Aliskiren
PRA reductions in clinical trials ranged from
approximately 50% to 80%, were not dose-related and did not correlate with
blood pressure reductions. The clinical implications of the differences in
effect on PRA are not known.
Hydrochlorothiazide
After oral administration of hydrochlorothiazide,
diuresis begins within 2 hours, peaks in about 4 hours, and lasts about 6 to 12
hours.
Drug Interactions
Hydrochlorothiazide
Alcohol, barbiturates, or narcotics: Potentiation
of orthostatic hypotension may occur.
Skeletal muscle relaxants: Possible increased
responsiveness to muscle relaxants such as curare derivatives.
Digitalis glycosides: Thiazide-induced hypokalemia
or hypomagnesemia may predispose the patient to digoxin toxicity.
Pharmacokinetics
Absorption and Distribution
Tekturna HCT
Following oral administration of Tekturna HCT combination
tablets, the median peak plasma concentration time is within 1 hour for
aliskiren and 2.5 hours for hydrochlorothiazide. When taken with food, mean AUC
and Cmax of aliskiren are decreased by 60% and 82%, respectively; mean AUC and
Cmax of hydrochlorothiazide increased by 13% and 10%, respectively. As a
result, patients should establish a routine pattern for taking Tekturna HCT
with regard to meals.
Aliskiren
Aliskiren is poorly absorbed (bioavailability about
2.5%). Following oral administration, peak plasma concentrations of aliskiren
are reached within 1 to 3 hours. When taken with a high fat meal, mean AUC and
Cmax of aliskiren are decreased by 71% and 85% respectively. In the clinical
trials of aliskiren, it was administered without requiring a fixed relation of
administration to meals.
Hydrochlorothiazide
The estimated absolute bioavailability of
hydrochlorothiazide after oral administration is about 70%. Peak plasma
hydrochlorothiazide concentrations (Cmax) are reached within 2 to 5 hours after
oral administration. There is no clinically significant effect of food on the
bioavailability of hydrochlorothiazide.
Hydrochlorothiazide binds to albumin (40 to 70%) and
distributes into erythrocytes. Following oral administration, plasma
hydrochlorothiazide concentrations decline bi-exponentially, with a mean
distribution half-life of about 2 hours and an elimination half-life of about
10 hours.
Metabolism and Elimination
Aliskiren
The effective half-life for aliskiren is 24 hours. Steady
state blood levels are reached in about 7 – 8 days. About one-fourth of the
absorbed dose appears in the urine as parent drug. How much of the absorbed
dose is metabolized is unknown. Based on the in vitro studies, the major enzyme
responsible for aliskiren metabolism appears to be CYP 3A4. Aliskiren does not
inhibit the CYP450 isoenzymes (CYP 1A2, 2C8, 2C9, 2C19, 2D6, 2E1, and 3A) or
induce CYP 3A4.
Transporters: Pgp (MDR1/Mdr1a/1b) was found to be
the major efflux system involved in absorption and disposition of aliskiren in
preclinical studies. The potential for drug interactions at the Pgp site will
likely depend on the degree of inhibition of this transporter.
Hydrochlorothiazide
About 70% of an orally administered dose of
hydrochlorothiazide is eliminated in the urine as unchanged drug.
Drug interactions
Aliskiren
The effect of co-administered drugs on the
pharmacokinetics of aliskiren and vice versa, were studied in several single
and multiple dose studies. Pharmacokinetic measures indicating the magnitude of
these interactions are presented in Figure 5 (impact of co-administered drugs
on aliskiren) and Figure 6 (impact on co-administered drugs).
Figure 5: The impact of co-administered drugs on the
pharmacokinetics of aliskiren
Warfarin: There was no clinically significant
effect of a single dose of warfarin 25 mg on the pharmacokinetics of aliskiren.
Figure 6: The impact of aliskiren on the pharmacokinetics
of co-administered drugs
Furosemide: In patients with heart failure, co-administration of
aliskiren (300 mg/day) reduced plasma AUC and Cmax of oral furosemide (60
mg/day) by 17% and 27%, respectively, and reduced 24 hour urinary furosemide
excretion by 29%. This change in exposure did not result in statistically
significant difference in total urine volume and urinary sodium excretion over
24 hours. However, a transient decrease in urinary sodium excretion and urine
volume effects up to 12 hours were observed when furosemide was co-administered
with aliskiren 300 mg/day.
Hydrochlorothiazide
Drugs that alter
gastrointestinal motility: The bioavailability of thiazide-type diuretics may be
increased by anticholinergic agents (e.g. atropine, biperiden), apparently due
to a decrease in gastrointestinal motility and the stomach emptying rate.
Conversely, pro-kinetic drugs may decrease the bioavailability of thiazide
diuretics.
Cholestyramine: In a dedicated drug
interaction study, administration of cholestyramine 2 hours before
hydrochlorothiazide resulted in a 70% reduction in exposure to
hydrochlorothiazide. Further, administration of hydrochlorothiazide 2 hours
before cholestyramine, resulted in 35% reduction in exposure to
hydrochlorothiazide.
Antineoplastic agents (e.g.
cyclophosphamide, methotrexate): Concomitant use of thiazide diuretics may reduce renal
excretion of cytotoxic agents and enhance their myelosuppressive effects.
Special Populations
Pediatric Patients
The pharmacokinetics of aliskiren have not been
investigated in patients < 18 years of age.
Geriatric Patients
Aliskiren
The pharmacokinetics of aliskiren were studied in the
elderly ( ≥ 65 years). Exposure (measured by AUC) is increased in elderly
patients. Hydrochlorothiazide A limited amount of data suggest that the
systemic clearance of hydrochlorothiazide is reduced in both healthy and
hypertensive elderly subjects compared to young healthy volunteers.
Race
Too few non-Caucasians have been studied with Tekturna
HCT to assess pharmacokinetic differences among races. The pharmacokinetic
differences among Blacks, Caucasians, and Japanese are minimal with aliskiren
therapy.
Renal Impairment
Aliskiren
The pharmacokinetics of aliskiren were evaluated in patients
with varying degrees of renal impairment. Rate and extent of exposure (AUC and
Cmax) of aliskiren in subjects with renal impairment did not show a consistent
correlation with the severity of renal impairment [see Use in Specific
Populations].
The pharmacokinetics of aliskiren following
administration of a single oral dose of 300 mg was evaluated in patients with
End Stage Renal Disease (ESRD) undergoing hemodialysis. When compared to
matched healthy subjects, changes in the rate and extent of aliskiren exposure
(Cmax and AUC) in ESRD patients undergoing hemodialysis were not clinically
significant.
Timing of hemodialysis did not significantly alter the
pharmacokinetics of aliskiren in ESRD patients. Therefore, no dose adjustment
is warranted in ESRD patients receiving hemodialysis.
Hydrochlorothiazide
In a study in individuals with impaired renal function,
the mean elimination half-life of hydrochlorothiazide was doubled in
individuals with mild/moderate renal impairment (30 < CLcr < 90 mL/min)
and tripled in severe renal impairment ( ≤ 30 mL/min), compared to
individuals with normal renal function (CLcr > 90 mL/min) [see Use in
Specific Populations].
Hepatic Impairment
Aliskiren
The pharmacokinetics of aliskiren were not significantly
affected in patients with mild-to-severe liver disease [see Use in Specific
Populations].
Clinical Studies
Tekturna HCT
In all clinical trials including over 6,200 patients,
more than 2,700 patients were exposed to combinations of aliskiren and
hydrochlorothiazide. The safety and efficacy of Tekturna HCT were evaluated in
patients with mild-to-moderate hypertension in an 8-week, randomized,
double-blind, placebo-controlled, parallel-group, 15arm factorial trial
(n=2762). Patients were randomized to receive various combinations of aliskiren
(75 mg to 300 mg) plus hydrochlorothiazide (6.25 mg to 25 mg) once daily
(without titrating up from monotherapy) and followed for blood pressure
response. The combination of aliskiren and hydrochlorothiazide resulted in
additive placebo-adjusted decreases in systolic and diastolic blood pressure at
trough of 10-14/5-7 mmHg at doses of 150-300 mg/12.5-25 mg, compared to 5-8/2-3
mmHg for aliskiren 150 mg to 300 mg and 6-7/2-3 mmHg for hydrochlorothiazide
12.5 mg to 25 mg, alone. Blood pressure reductions with the combinations were
greater than the reductions with the monotherapies as shown in Table 1.
Table 1: Placebo-Subtracted Reductions in Seated
Trough Cuff Blood Pressure in Combination with Hydrochlorothiazide
Aliskiren, mg |
Placebo Mean Change |
Hydrochlorothiazide, mg |
0 |
6.25 |
12.5 |
25 |
Placebo- subtracted |
Placebo- subtracted |
Placebo- subtracted |
Placebo- subtracted |
0 |
7.5/6.9 |
-- |
3.5/2.1 |
6.4/3.2 |
6.8/2.4 |
75 |
-- |
1.9/1.8 |
6.8/3.8 |
8.2/4.2 |
9.8/4.5 |
150 |
-- |
4.8/2 |
7.8/3.4 |
10.1/5 |
12/5.7 |
300 |
-- |
8.3/3.3 |
-- |
12.3/7 |
13.7/7.3 |
The safety and efficacy of
Tekturna HCT as initial therapy was evaluated in this trial. All patients
randomized to the combination groups received the combination treatment of
Tekturna HCT at assigned doses as initial therapy without titration from
monotherapy. The figures [see INDICATIONS AND USAGE] display the
probability that a patient will achieve systolic or diastolic blood pressure
goal with Tekturna HCT 300/25 mg, based upon their baseline systolic or
diastolic blood pressure. At all levels of baseline blood pressure, the
probability of achieving any given diastolic or systolic goal is greater with
the combination than for either monotherapy.
The antihypertensive effect of
Tekturna HCT was largely manifested within 1 week. The maximum antihypertensive
effect was generally attained after about 4 weeks of therapy.
One active-controlled trial
investigated the addition of 300 mg aliskiren in obese hypertensive patients
who did not respond adequately to hydrochlorothiazide 25 mg, and showed
incremental decreases of systolic and diastolic blood pressure of approximately
7/4 mmHg.
In long-term follow-up studies
(without placebo control) the effect of the combination of aliskiren and
hydrochlorothiazide was maintained for over 1 year.
The antihypertensive effect was
independent of age and gender. There were too few non-Caucasians to assess
differences in blood pressure effects by race.
Aliskiren Monotherapy
The antihypertensive effects of
aliskiren have been demonstrated in six randomized, double-blind,
placebo-controlled, 8-week clinical trials in patients with mild-to-moderate
hypertension. The placebo response and placebo-subtracted changes from baseline
in seated trough cuff blood pressure are shown in Table 2.
Table 2: Reductions in
Seated Trough Cuff Blood Pressure in the Placebo-Controlled Studies of
Aliskiren Monotherapy
Study |
Placebo Mean Change |
Aliskiren Daily Dose, mg |
75 |
150 |
300 |
600 |
Placebo-subtracted |
Placebo-subtracted |
Placebo-subtracted |
Placebo-subtracted |
1 |
2.9/3.3 |
5.7/4* |
5.9/4.5* |
11.2/7.5* |
-- |
2 |
5.3/6.3 |
-- |
6.1/2.9* |
10.5/5.4* |
10.4/5.2* |
3 |
10/8.6 |
2.2/1.7 |
2.1/1.7 |
5.1/3.7* |
-- |
4 |
7.5/6.9 |
1.9/1.8 |
4.8/2* |
8.3/3.3* |
-- |
5 |
3.8/4.9 |
-- |
9.3/5.4* |
10.9/6.2* |
12.1/7.6* |
6 |
4.6/4.1 |
-- |
-- |
8.4/4.91† |
-- |
*p < 0.05 vs. placebo by ANCOVA with Dunnett's procedure
for multiple comparisons.
†p < 0.05 vs. placebo by ANCOVA for the pairwise comparison |
The studies included
approximately 2,730 patients given doses of 75 mg to 600 mg of aliskiren and
1,231 patients given placebo. As shown in Table 2, there is some increase in
response with administered dose in all studies, with reasonable effects seen at
150 mg to 300 mg, and no clear further increase at 600 mg. A substantial
proportion (85% to 90%) of the blood pressure lowering effect was observed
within 2 weeks of treatment. Studies with ambulatory blood pressure monitoring
showed reasonable control throughout the interdosing interval, e.g., the ratios
of mean daytime to mean nighttime ambulatory BP ranged from 0.6 to 0.9.
Patients in the
placebo-controlled trials continued open-label aliskiren for up to one year. A
persistent blood pressure lowering effect was demonstrated by a randomized
withdrawal study (patients randomized to continued drug or placebo), which
showed a statistically significant difference between patients kept on
aliskiren and those randomized to placebo. With cessation of treatment, blood
pressure gradually returned toward baseline levels over a period of several
weeks. There was no evidence of rebound hypertension after abrupt cessation of
therapy.
The effectiveness of aliskiren
was demonstrated across all demographic subgroups, although Black patients
tended to have smaller reductions in blood pressure than Caucasians and Asians,
as has been seen with ACE inhibitors and ARBs.
Aliskiren in Combination with
Other Antihypertensives
Valsartan
Aliskiren 150 mg and 300 mg and
valsartan 160 mg and 320 mg were studied alone and in combination in an 8week,
1,797-patient, randomized, double-blind, placebo-controlled, parallel-group,
4-arm, dose-escalation study. The dosages of aliskiren and valsartan were
started at 150 mg and 160 mg, respectively, and increased at four weeks to 300
mg and 320 mg, respectively. Seated trough cuff blood pressure was measured at
baseline, 4, and 8 weeks. Blood pressure reductions with the combinations were
greater than the reductions with the monotherapies as shown in Table 3.
Table 3: Placebo-Subtracted
Reductions in Seated Trough Cuff Blood Pressure of Aliskiren in Combination
with Valsartan
Aliskiren, mg |
Placebo Mean Change |
Valsartan, mg |
0 |
160 |
320 |
0 |
4.6/4.1* |
-- |
5.6/3.9 |
8.2/5.6 |
150 |
-- |
5.4/2.7 |
10.0/5.7 |
-- |
300 |
-- |
8.4/4.9 |
-- |
12.6/8.1 |
* The placebo change is 5.2/4.8
for Week 4 endpoint which was used for the dose groups containing aliskiren 150
mg or valsartan 160 mg. |
Amlodipine
Aliskiren 150 mg and 300 mg and amlodipine besylate 5 mg
and 10 mg were studied alone and in combination in an 8week, 1,685-patient,
randomized, double-blind, placebo-controlled, multifactorial study. Treatment
with aliskiren and amlodipine resulted overall in significantly greater
reductions in diastolic and systolic blood pressure compared to the respective
monotherapy components as shown in Table 4.
Table 4: Placebo-Subtracted Reductions in Seated
Trough Cuff Blood Pressure in Combination with Amlodipine
Aliskiren, mg |
Placebo mean change |
Amlodipine, mg |
0 |
5 |
10 |
0 |
5.4/6.8 |
__ |
5.6/9.0 |
8.5/14.3 |
150 |
-- |
2.6/3.9 |
8.6/13.9 |
10.8/17.1 |
300 |
-- |
4.9/8.6 |
9.6/15.0 |
11.1/16.4 |
ACE Inhibitors
Aliskiren has not been studied
when added to maximal doses of ACE inhibitors to determine whether aliskiren
produces additional blood pressure reduction.
There are no trials of the
Tekturna HCT combination tablet demonstrating reductions in cardiovascular risk
in patients with hypertension, but the hydrochlorothiazide component has
demonstrated such benefits.
Aliskiren in Patients with
Diabetes treated with ARB or ACEI (ALTITUDE study)
Patients with diabetes with
renal disease (defined either by the presence of albuminuria or reduced GFR)
were randomized to aliskiren 300 mg daily (n=4283) or placebo (n=4296). All
patients were receiving background therapy with an ARB or ACEI. The primary
efficacy outcome was the time to the first event of the primary composite
endpoint consisting of cardiovascular death, resuscitated sudden death,
non-fatal myocardial infarction, non-fatal stroke, unplanned hospitalization
for heart failure, onset of end stage renal disease, renal death, and doubling
of serum creatinine concentration from baseline sustained for at least one
month. After a median follow up of about 27 months, the trial was terminated
early for lack of efficacy. Higher risk of renal impairment, hypotension and
hyperkalemia was observed in aliskiren compared to placebo treated patients, as
shown in the table below.
Table 5: Incidence of
selected adverse events in ALTITUDE
|
Aliskiren
N=4283 |
Placebo
N=4296 |
Serious Adverse Events* (%) |
Adverse Events (%) |
Serious Adverse Events* (%) |
Adverse Events (%) |
Renal impairment† |
4.7 |
12.4 |
3.3 |
10.4 |
Hypotension †† |
2.0 |
18.6 |
1.7 |
14.8 |
Hyperkalemia††† |
1.1 |
36.9 |
0.3 |
27.1 |
†renal failure, renal failure
acute, renal failure chronic, renal impairment
††dizziness, dizziness postural, hypotension, orthostatic hypotension,
presyncope, syncope
††† Given the variable baseline potassium levels of patients with renal
insufficiency on dual RAAS therapy, the reporting of adverse event of
hyperkalemia was at the discretion of the investigator.
* A Serious Adverse Event (SAE) is defined as: an event which is fatal or
life-threatening, results in persistent or significant disability/incapacity,
constitutes a congenital anomaly/birth defect, requires inpatient
hospitalization or prolongation of existing hospitalization, or is medically
significant (i.e. defined as an event that jeopardizes the patient or may
require medical or surgical intervention to prevent one of the outcomes
previously listed). |
The risk of stroke (2.7% aliskiren vs 2.0% placebo) and
death (6.9% aliskiren vs. 6.4% placebo) were also numerically higher in
aliskiren treated patients.