Mechanism of Action
Nicardipine is a calcium entry blocker (slow channel blocker
or calcium ion antagonist) that inhibits the transmembrane influx of calcium
ions into cardiac muscle and smooth muscle without changing serum calcium
concentrations. The contractile processes of cardiac muscle and vascular smooth
muscle are dependent upon the movement of extracellular calcium ions into these
cells through specific ion channels. The effects of nicardipine are more
selective to vascular smooth muscle than cardiac muscle. In animal models,
nicardipine produces relaxation of coronary vascular smooth muscle at drug
levels that cause little or no negative inotropic effect.
Pharmacokinetics and Metabolism
Nicardipine is completely absorbed following oral doses
administered as capsules, and the systemic bioavailability is about 35%
following 30-mg oral dose at steady-state. The pharmacokinetics of nicardipine
are nonlinear due to saturable hepatic first-pass metabolism.
Following oral administration of CARDENE SR, plasma levels
are detectable as early as 20 minutes and maximal plasma levels are achieved as
a broad peak generally between 1 and 4 hours. The average terminal plasma
half-life of nicardipine is 8.6 hours. Following oral administration increasing
doses result in disproportionate increases in plasma levels. Steady-state Cmax
values following 30-, 45- and 60-mg doses every 12 hours averaged 13.4, 34.0,
and 58.4 ng/mL, respectively. Hence, increasing the dose twofold increases
maximum plasma levels 4-fold to 5-fold. A similar disproportionate increase is
observed with AUC. In comparison with equivalent daily doses of CARDENE
capsules, CARDENE SR shows a significant reduction in Cmax. CARDENE SR also has
somewhat lower bioavailability than CARDENE except at the highest dose. Minimum
plasma levels produced by equivalent daily doses are similar. CARDENE SR thus
exhibits significantly reduced fluctuation in plasma levels in comparison to
CARDENE capsules.
When CARDENE SR was administered with a high-fat breakfast,
mean Cmax was 45% lower, AUC was 25% lower and trough levels were 75% higher
than when CARDENE SR was given in the fasting state. Thus, taking CARDENE SR
with the meal reduced the fluctuation in plasma levels. Clinical trials
establishing the safety and efficacy of CARDENE SR were carried out in patients
without regard to the timing of meals.
Nicardipine is highly protein bound ( > 95%) in human
plasma over wide concentration range.
Nicardipine is metabolized extensively by the liver; less
than 1% of intact drug is detected in the urine. Following a radioactive oral
dose in solution, 60% of the radioactivity was recovered in the urine and 35%
in feces. Most of the dose (over 90%) was recovered within 48 hours of dosing.
Nicardipine does not induce its own metabolism and does not induce hepatic
microsomal enzymes.
Nicardipine plasma levels following administration of
CARDENE SR in hypertensive patients with moderate renal impairment (creatinine
clearance 10 to 55 mL/min) were significantly higher following a single-oral dose
and at steady-state than in hypertensive patients with mildly nicardipine
hydrochloride impaired renal function (creatinine clearance > 55 mL/min).
After 45-mg CARDENE SR bid at steady-state, Cmax and AUC were 2-fold to 3-fold higher
in the patients with moderate renal impairment. Plasma levels in patients with
mildly impaired renal function were similar to those in normal subjects.
In patients with severe renal impairment undergoing routine
hemodialysis, plasma levels following a single dose of CARDENE SR were not significantly
different from those patients with mildly impaired renal function.
Because nicardipine is extensively metabolized by the liver,
the plasma levels of the drug are influenced by changes in hepatic function. Following
administration of CARDENE capsules, nicardipine plasma levels were higher in
patients with severe liver disease (hepatic cirrhosis confirmed by liver biopsy
or presence of endoscopically-confirmed esophageal varices) than in normal
subjects. After 20-mg CARDENE bid at steady-state, Cmax and AUC were 1.8-fold
and 4-fold higher, and the terminal half-life was prolonged to 19 hours in
these patients. CARDENE SR has not been studied in patients with severe liver
disease.
Geriatric Pharmacokinetics
The pharmacokinetics of CARDENE SR in elderly hypertensive
subjects mean age 70 years) were compared to those in younger hypertensive subjects
(mean age 44 years). After a single dose and after 1 week of dosing with
CARDENE SR there were no significant differences in Cmax, Tmax, AUC or
clearance between the young and elderly subjects. In both groups of subjects,
steady-state plasma levels were significantly higher than following a single
dose. In the elderly subjects, a disproportional increase in plasma levels with
dose was observed similar to that observed in normal subjects.
Hemodynamics
In man, nicardipine produces a significant decrease in
systemic vascular resistance. The degree of vasodilation and the resultant
hypotensive effects are more prominent in hypertensive patients. In
hypertensive patients, nicardipine reduces the blood pressure at rest and
during isometric and dynamic exercise. In normotensive patients, a small decrease
of about 9 mm Hg in systolic and 7 mm Hg in diastolic blood pressure may
accompany this fall in peripheral resistance. An increase in heart rate may
occur in response to the vasodilation and decrease in blood pressure, and in a
few patients this heart rate increase may be pronounced. In clinical studies
mean heart rate at time of peak plasma levels was usually increased by 5 to 10
beats per minute compared to placebo, with the greater increases at higher
doses, while there was no difference from placebo at the end of the dosing
interval. Hemodynamic studies following intravenous dosing in patients with
coronary artery disease and normal or moderately abnormal left ventricular
function have shown significant increases in ejection fraction and cardiac
output CARDENE® SR (nicardipine hydrochloride) with no significant change, or a
small decrease, in left ventricular enddiastolic pressure (LVEDP). Although
there is evidence that nicardipine increases coronary blood flow, there is no
evidence that this property plays any role in its effectiveness in stable
angina. In patients with coronary artery disease, intracoronary administration
of nicardipine caused no direct myocardial depression. CARDENE does, however,
have a negative inotropic effect in some patients with severe left ventricular dysfunction
and could, in patients with very impaired function, lead to worsened failure.
“Coronary Steal,” the detrimental redistribution of coronary
blood flow in patients with coronary artery disease (diversion of blood from
underperfused areas toward better perfused areas), has not been observed during
nicardipine treatment. On the contrary, nicardipine has been shown to improve
systolic shortening in normal and hypokinetic segments of myocardial muscle,
and radionuclide angiography has confirmed that wall motion remained improved
during an increase in oxygen demand. Nonetheless, occasional patients have
developed increased angina upon receiving nicardipine. Whether this represents steal
in those patients, or is the result of increased heart rate and decreased
diastolic pressure, is not clear.
In patients with coronary artery disease nicardipine
improves L.V. diastolic distensibility during the early filling phase, probably
due to a faster rate of myocardial relaxation in previously underperfused
areas. There is little or no effect on normal myocardium, suggesting the
improvement is mainly by indirect mechanisms such as afterload reduction and
reduced ischemia. Nicardipine has no negative effect on myocardial relaxation
at therapeutic doses. The clinical consequences of these properties are as yet
undemonstrated.
Electrophysiologic Effects
In general, no detrimental effects on the cardiac conduction
system were seen with the use of CARDENE.
Nicardipine increased the heart rate when given
intravenously during acute electrophysiologic studies and prolonged the
corrected QT interval to a minor degree. The sinus node recovery times and SA
conduction times were not affected by the drug. The PA, AH and HV intervals*
and the functional and effective refractory periods of the atrium were not prolonged
by nicardipine and the relative and effective refractory periods
of the His-Purkinje system were slightly shortened after
intravenous nicardipine.
Renal Function
There is a transient increase in electrolyte excretion,
including sodium. CARDENE does not cause generalized fluid retention, as
measured by weight changes.
Effects in Hypertension
CARDENE SR produced decreases in both systolic and diastolic
blood pressure throughout the dosing interval in clinical trials. The
antihypertensive efficacy of CARDENE SR administered twice daily has been demonstrated
using in-clinic blood pressure measures in placebocontrolled trials involving
patients with mild to moderate hypertension and in trials using 12 or 24 hour
ambulatory blood pressure monitoring.
REFERENCES
*PA=conduction time from high to low right atrium, AH=conduction
time from low right atrium to His bundle deflection or AV nodal conduction time,
HV=conduction time through the His bundle and the bundle branch-Purkinje system.
Last updated on RxList: 6/19/2009