CLINICAL PHARMACOLOGY
Mechanism Of Action
Lisinopril inhibits angiotensin converting enzyme (ACE)
in human subjects and animals. ACE is a peptidyl dipeptidase that catalyzes the
conversion of angiotensin I to the vasoconstrictor substance, angiotensin II. Angiotensin
II also stimulates aldosterone secretion by the adrenal cortex. The beneficial
effects of lisinopril in hypertension and heart failure appear to result
primarily from suppression of the renin- angiotensin-aldosterone system.
Inhibition of ACE results in decreased plasma angiotensin II which leads to
decreased vasopressor activity and to decreased aldosterone secretion. The
latter decrease may result in a small increase of serum potassium. In
hypertensive patients with normal renal function treated with PRINIVIL alone
for up to 24 weeks, the mean increase in serum potassium was approximately 0.1
mEq/L; however, approximately 15% of patients had increases greater than 0.5
mEq/L and approximately 6% had a decrease greater than 0.5 mEq/L. In the same
study, patients treated with PRINIVIL and hydrochlorothiazide for up to 24
weeks had a mean decrease in serum potassium of 0.1 mEq/L; approximately 4% of
patients had increases greater than 0.5 mEq/L and approximately 12% had a decrease
greater than 0.5 mEq/L [see WARNINGS AND PRECAUTIONS]. Removal of
angiotensin II negative feedback on renin secretion leads to increased plasma
renin activity.
ACE is identical to kininase, an enzyme that degrades
bradykinin. Whether increased levels of bradykinin, a potent vasodepressor
peptide, play a role in the therapeutic effects of PRINIVIL remains to be elucidated.
While the mechanism through which PRINIVIL lowers blood
pressure is believed to be primarily suppression of the
renin-angiotensin-aldosterone system, PRINIVIL is antihypertensive even in
patients with low-renin hypertension. Although PRINIVIL was antihypertensive in
all races studied, Black hypertensive patients (usually a low-renin
hypertensive population) had a smaller average response to monotherapy than
non-Black patients.
Concomitant administration of PRINIVIL and
hydrochlorothiazide further reduced blood pressure in Black and non-Black
patients and any racial difference in blood pressure response was no longer
evident.
Pharmacodynamics
Hypertension
Adult Patients
Administration of PRINIVIL to patients with hypertension
results in a reduction of supine and standing blood pressure to about the same
extent with no compensatory tachycardia. Symptomatic postural hypotension is
usually not observed although it can occur and should be anticipated in volume and/or
salt-depleted patients [see WARNINGS AND PRECAUTIONS]. When given
together with thiazidetype diuretics, the blood pressure lowering effects of
the two drugs are approximately additive.
In most patients studied, onset of antihypertensive
activity was seen at one hour after oral administration of an individual dose
of PRINIVIL, with peak reduction of blood pressure achieved by 6 hours.
Although an antihypertensive effect was observed 24 hours after dosing with
recommended single daily doses, the effect was more consistent and the mean
effect was considerably larger in some studies with doses of 20 mg or more than
with lower doses. However, at all doses studied, the mean antihypertensive
effect was substantially smaller 24 hours after dosing than it was 6 hours
after dosing.
The antihypertensive effects of PRINIVIL are maintained
during long-term therapy. Abrupt withdrawal of PRINIVIL has not been associated
with a rapid increase in blood pressure or a significant increase in blood
pressure compared to pretreatment levels.
Pharmacokinetics
Adult Patients
Following oral administration of PRINIVIL, peak serum
concentrations of lisinopril occur within about 7 hours, although there was a
trend to a small delay in time taken to reach peak serum concentrations in
acute myocardial infarction patients. Declining serum concentrations exhibit a
prolonged terminal phase which does not contribute to drug accumulation. This
terminal phase probably represents saturable binding to ACE and is not
proportional to dose. Upon multiple dosing, lisinopril exhibits an effective half-life
of 12 hours.
Lisinopril does not appear to be bound to other serum
proteins. Lisinopril does not undergo metabolism and is excreted unchanged
entirely in the urine. Based on urinary recovery, the mean extent of absorption
of lisinopril is approximately 25 percent, with large inter-subject variability
(6-60 percent) at all doses tested (5-80 mg). Lisinopril absorption is not
influenced by the presence of food in the gastrointestinal tract. The absolute
bioavailability of lisinopril is reduced to about 16 percent in patients with
stable NYHA Class II-IV congestive heart failure, and the volume of
distribution appears to be slightly smaller than that in normal subjects.
The oral bioavailability of lisinopril in patients with acute
myocardial infarction is similar to that in healthy volunteers.
Impaired renal function decreases elimination of
lisinopril, which is excreted principally through the kidneys, but this
decrease becomes clinically important only when the glomerular filtration rate
is below 30 mL/min. Above this glomerular filtration rate, the elimination
half-life is little changed. With greater impairment, however, peak and trough
lisinopril levels increase, time to peak concentration increases and time to
attain steady state is prolonged. Older patients, on average, have
(approximately doubled) higher blood levels and area under the plasma
concentration time curve (AUC) than younger patients [see DOSAGE AND
ADMINISTRATION]. Lisinopril can be removed by hemodialysis.
Studies in rats indicate that lisinopril crosses the
blood-brain barrier poorly. Multiple doses of lisinopril in rats do not result
in accumulation in any tissues. Milk of lactating rats contains radioactivity
following administration of 14C lisinopril. By whole body autoradiography,
radioactivity was found in the placenta following administration of labeled
drug to pregnant rats, but none was found in the fetuses.
Pediatric Patients
The pharmacokinetics of lisinopril were studied in 29 pediatric
hypertensive patients between 6 years and 16 years with glomerular filtration
rate >30 mL/min/1.73 m². After doses of 0.1 to 0.2 mg/kg, steady state peak
plasma concentrations of lisinopril occurred within 6 hours and the extent of absorption
based on urinary recovery was about 28%. These values are similar to those
obtained previously in adults. The typical value of lisinopril oral clearance
(systemic clearance/absolute bioavailability) in a child weighing 30 kg is 10
L/h, which increases in proportion to renal function.
Clinical Studies
Hypertension
Adult Patients
Two dose-response studies utilizing a once daily regimen
were conducted in 438 mild to moderate hypertensive patients not on a diuretic.
Blood pressure was measured 24 hours after dosing. An antihypertensive effect
of PRINIVIL was seen with 5 mg in some patients. However, in both studies blood
pressure reduction occurred sooner and was greater in patients treated with 10,
20, or 80 mg of PRINIVIL. In controlled clinical studies in patients with mild
to moderate hypertension, PRINIVIL 20-80 mg has been compared to
hydrochlorothiazide 12.5-50 mg and with atenolol 50-500 mg, and in patients
with moderate, to severe hypertension to metoprolol 100-200 mg. It was superior
to hydrochlorothiazide in effects on systolic and diastolic blood pressure in a
population that was 75% Caucasian. PRINIVIL was approximately equivalent to
atenolol and metoprolol in effects on diastolic blood pressure and had somewhat
greater effects on systolic blood pressure.
PRINIVIL had similar effectiveness and adverse effects in
younger and older (>65 years) patients. It was less effective in Blacks than
in Caucasians.
In hemodynamic studies of PRINIVIL in patients with
essential hypertension, blood pressure reduction was accompanied by a reduction
in peripheral arterial resistance with little or no change in cardiac output and
in heart rate. In a study in nine hypertensive patients, following
administration of PRINIVIL, there was an increase in mean renal blood flow that
was not significant. Data from several small studies are inconsistent with
respect to the effect of lisinopril on glomerular filtration rate in
hypertensive patients with normal renal function, but suggest that changes, if
any, are not large.
In patients with renovascular hypertension PRINIVIL has
been shown to be well tolerated and effective in reducing blood pressure [see WARNINGS
AND PRECAUTIONS].
Pediatric Patients
In a clinical study involving 115 hypertensive pediatric
patients 6 to 16 years of age, patients who weighed <50 kg received either
0.625, 2.5, or 20 mg of lisinopril daily and patients who weighed ≥50 kg
received either 1.25, 5, or 40 mg of lisinopril daily. At the end of 2 weeks,
lisinopril administered once daily lowered trough blood pressure in a
dose-dependent manner with consistent antihypertensive efficacy demonstrated at
doses >1.25 mg (0.02 mg/kg). This effect was confirmed in a withdrawal
phase, where the diastolic pressure rose by about 9 mmHg more in patients
randomized to placebo than it did in patients who were randomized to remain on
the middle and high doses of lisinopril. The dose-dependent antihypertensive
effect of lisinopril was consistent across several demographic subgroups: age,
Tanner stage, gender, and race. In this study, lisinopril was generally
well-tolerated.
In the above pediatric studies, lisinopril was given
either as tablets or in a suspension for those children and infants who were
unable to swallow tablets or who required a lower dose than is available in
tablet form [see DOSAGE AND ADMINISTRATION].
Heart Failure
In two placebo controlled, 12-week clinical studies
compared the addition of PRINIVIL up to 20 mg daily to digitalis and diuretics
alone. The combination of PRINIVIL, digitalis and diuretics reduced the
following signs and symptoms of heart failure: edema, rales, paroxysmal
nocturnal dyspnea and jugular venous distention. In one of the studies, the
combination of PRINIVIL, digitalis and diuretics reduced orthopnea, presence of
third heart sound and the number of patients classified as NYHA Class III and
IV, and it improved exercise tolerance. A large (over 3000 patients) survival
study, the ATLAS Trial, comparing 2.5 and 35 mg of lisinopril in patients with
systolic heart failure, showed that the higher dose of lisinopril had outcomes
at least as favorable as the lower dose. During baseline-controlled clinical
trials, in patients receiving digitalis and diuretics, single doses of PRINIVIL
resulted in decreases in pulmonary capillary wedge pressure, systemic vascular
resistance and blood pressure accompanied by an increase in cardiac output and
no change in heart rate.
Acute Myocardial Infarction
The Gruppo Italiano per lo Studio della Sopravvienza
nell'Infarto Miocardico (GISSI-3) study was a multicenter, controlled,
randomized, unblinded clinical trial conducted in 19,394 patients with acute myocardial
infarction (MI) admitted to a coronary care unit. It was designed to examine
the effects of short-term (6 week) treatment with lisinopril, nitrates, their
combination, or no therapy on short-term (6 week) mortality and on long-term
death and markedly impaired cardiac function. Hemodynamically-stable patients
presenting within 24 hours of the onset of symptoms were randomized, in a 2 x 2
factorial design, to 6 weeks of either 1) PRINIVIL alone (n=4841), 2) nitrates
alone (n=4869), 3) PRINIVIL plus nitrates (n=4841), or 4) open control
(n=4843). All patients received routine therapies, including thrombolytics (72%),
aspirin (84%), and a beta blocker (31%), as appropriate, normally utilized in
acute myocardial infarction (MI) patients.
The protocol excluded patients with hypotension (systolic
blood pressure ≤100 mmHg), severe heart failure, cardiogenic shock, and
renal dysfunction (serum creatinine >2 mg/dL and/or proteinuria >500 mg per
24 h). Patients randomized to PRINIVIL received 5 mg within 24 hours of the
onset of symptoms, 5 mg after 24 hours, and then 10 mg daily thereafter.
Patients with systolic blood pressure less than 120 mmHg at baseline received
2.5 mg of PRINIVIL. If hypotension occurred, the PRINIVIL dose was reduced or
if severe hypotension occurred PRINIVIL was stopped [see DOSAGE AND
ADMINISTRATION].
The primary outcomes of the trial were the overall
mortality at 6 weeks and a combined endpoint at 6 months after the myocardial
infarction, consisting of the number of patients who died, had late (day 4) clinical
congestive heart failure, or had extensive left ventricular damage defined as
ejection fraction ≤35%, or an akinetic-dyskinetic [A-D] score ≥45%.
Patients receiving PRINIVIL (n=9646), alone or with nitrates, had an 11% lower
risk of death (p =0.04) compared to patients who did not receive PRINIVIL (n=9672)
(6.4% vs. 7.2%, respectively) at 6 weeks. Although patients randomized to
receive PRINIVIL for up to 6 weeks also fared numerically better on the
combined endpoint at 6 months, the open nature of the assessment of heart
failure, substantial loss to follow-up echocardiography, and substantial excess
use of PRINIVIL, between 6 weeks and 6 months in the group randomized to 6
weeks of lisinopril, preclude any conclusion about this endpoint.
Patients with acute myocardial infarction, treated with
PRINIVIL, had a higher (9.0% versus 3.7%) incidence of persistent hypotension
(systolic blood pressure <90 mmHg for more than 1 hour) and renal dysfunction
(2.4% versus 1.1%) in-hospital and at 6 weeks (increasing creatinine
concentration to over 3 mg/dL or a doubling or more of the baseline serum
creatinine concentration) [see ADVERSE REACTIONS].