Label: NIFEDIPINE tablet, extended release

Mechanism of Action

The mechanism by which nifedipine reduces arterial blood pressure involves peripheral arterial vasodilatation and, consequently, a reduction in peripheral vascular resistance. The increased peripheral vascular resistance, an underlying cause of hypertension, results from an increase in active tension in the vascular smooth muscle. Studies have demonstrated that the increase in active tension reflects an increase in cytosolic free calcium.

Nifedipine is a peripheral arterial vasodilator which acts directly on vascular smooth muscle. The binding of nifedipine to voltage-dependent and possibly receptor-operated channels in vascular smooth muscle results in an inhibition of calcium influx through these channels. Stores of intracellular calcium in vascular smooth muscle are limited and thus dependent upon the influx of extracellular calcium for contraction to occur. The reduction in calcium influx by nifedipine causes arterial vasodilation and decreased peripheral vascular resistance which results in reduced arterial blood pressure.

Pharmacokinetics and Metabolism

Nifedipine is completely absorbed after oral administration. The bioavailability of nifedipine as nifedipine extended-release tablet relative to immediate-release nifedipine is in the range of 84% to 89%. After ingestion of nifedipine extended-release tablets under fasting conditions, plasma concentrations peak at about 2.5 to 5 hours with a second small peak or shoulder evident at approximately 6 to 12 hours post dose. The elimination half-life of nifedipine administered as nifedipine extended-release tablet is approximately 7 hours in contrast to the known 2 hour elimination half-life of nifedipine administered as an immediate-release capsule.

When nifedipine extended-release tablet is administered as multiples of 30 mg tablets over a dose range of 30 mg to 90 mg, the area under the curve (AUC) is dose proportional; however, the peak plasma concentration for the 90 mg dose given as 3 × 30 mg is 29% greater than predicted from the 30 mg and 60 mg doses.

Two 30 mg nifedipine extended-release tablets may be interchanged with a 60 mg nifedipine extended-release tablet. Three 30 mg nifedipine extended-release tablets, however, result in substantially higher Cmax values than those after a single 90 mg nifedipine extended-release tablet. Three 30 mg tablets should, therefore, not be considered interchangeable with a 90 mg tablet.

Once daily dosing of nifedipine extended-release tablets under fasting conditions results in decreased fluctuations in the plasma concentration of nifedipine when compared to t.i.d. dosing with immediate-release nifedipine capsules. The mean peak plasma concentration of nifedipine following a 90 mg nifedipine extended-release tablet, administered under fasting conditions, is approximately 115 ng/mL. When nifedipine extended-release tablet is given immediately after a high fat meal in healthy volunteers, there is an average increase of 60% in the peak plasma nifedipine concentration, a prolongation in the time to peak concentration, but no significant change in the AUC. Plasma concentrations of nifedipine when nifedipine extended-release tablet is taken after a fatty meal result in slightly lower peaks compared to the same daily dose of the immediate-release formulation administered in three divided doses. This may be, in part, because nifedipine extended-release tablet is less bioavailable than the immediate-release formulation.

Nifedipine is extensively metabolized to highly water soluble, inactive metabolites accounting for 60% to 80% of the dose excreted in the urine. Only traces (less than 0.1% of the dose) of the unchanged form can be detected in the urine. The remainder is excreted in the feces in metabolized form, most likely as a result of biliary excretion.

Nifedipine is metabolized via the cytochrome P450 3A4 system. Drugs that are known to either inhibit or induce this enzyme system may alter the first pass or clearance of nifedipine.

No studies have been performed with nifedipine extended-release tablets in patients with renal failure; however, significant alterations in the pharmacokinetics of nifedipine immediate-release capsules have not been reported in patients undergoing hemodialysis or chronic ambulatory peritoneal dialysis. Since the absorption of nifedipine from nifedipine extended-release tablets could be modified by renal disease, caution should be exercised in treating such patients.

Because nifedipine is metabolized via the cytochrome P450 3A4 system, its pharmacokinetics may be altered in patients with chronic liver disease. Nifedipine extended-release tablets have not been studied in patients with hepatic disease; however, in patients with hepatic impairment (liver cirrhosis), nifedipine has a longer elimination half-life and higher bioavailability than in healthy volunteers.

The degree of protein binding of nifedipine is high (92% to 98%). Protein binding may be greatly reduced in patients with renal or hepatic impairment.

After administration of nifedipine extended-release tablets to healthy elderly men and women (age >60 years), the mean Cmax is 36% higher and the average plasma concentration is 70% greater than in younger patients.

In healthy subjects, the elimination half-life of a different sustained-release nifedipine formulation was longer in elderly subjects (6.7 h) compared to young subjects (3.8 h) following oral administration. A decreased clearance was also observed in the elderly (348 mL/min) compared to young subjects (519 mL/min) following intravenous administration.

Coadministration of nifedipine with grapefruit juice results in up to a 2-fold increase in AUC and Cmax due to inhibition of CYP3A related first-pass metabolism. Ingestion of grapefruit and grapefruit juice should be avoided while taking nifedipine.

Clinical Studies

Nifedipine extended-release tablets produced dose-related decreases in systolic and diastolic blood pressure as demonstrated in two double-blind, randomized, placebo-controlled trials in which over 350 patients were treated with nifedipine extended-release tablets, 30, 60 or 90 mg once daily for 6 weeks. In the first study, nifedipine extended-release tablet was given as monotherapy and in the second study, nifedipine extended-release tablet was added to a beta-blocker in patients not controlled on a beta-blocker alone. The mean trough (24 hours post-dose) blood pressure results from these studies are shown below:

The trough/peak ratios estimated from 24 hour blood pressure monitoring ranged from 41% to 78% for diastolic and 46% to 91% for systolic blood pressure.

Hemodynamics

Like other slow-channel blockers, nifedipine exerts a negative inotropic effect on isolated myocardial tissue. This is rarely, if ever, seen in intact animals or man, probably because of reflex responses to its vasodilating effects. In man, nifedipine decreases peripheral vascular resistance which leads to a fall in systolic and diastolic pressures, usually minimal in normotensive volunteers (less than 5 to 10 mmHg systolic), but sometimes larger. With nifedipine extended-release tablets, these decreases in blood pressure are not accompanied by any significant change in heart rate. Hemodynamic studies of the immediate-release nifedipine formulation in patients with normal ventricular function have generally found a small increase in cardiac index without major effects on ejection fraction, left ventricular end-diastolic pressure (LVEDP), or volume (LVEDV). In patients with impaired ventricular function, most acute studies have shown some increase in ejection fraction and reduction in left ventricular filling pressure.

Electrophysiologic Effects

Although, like other members of its class, nifedipine causes a slight depression of sinoatrial node function and atrioventricular conduction in isolated myocardial preparations, such effects have not been seen in studies in intact animals or in man. In formal electrophysiologic studies, predominantly in patients with normal conduction systems, nifedipine administered as the immediate-release capsule has had no tendency to prolong atrioventricular conduction or sinus node recovery time, or to slow sinus rate.

Excessive Hypotension

Although in most patients the hypotensive effect of nifedipine is modest and well tolerated, occasional patients have had excessive and poorly tolerated hypotension. These responses have usually occurred during initial titration or at the time of subsequent upward dosage adjustment, and may be more likely in patients using concomitant beta-blockers.

Severe hypotension and/or increased fluid volume requirements have been reported in patients who received immediate-release capsules together with a beta-blocking agent and who underwent coronary artery bypass surgery using high-dose fentanyl anesthesia. The interaction with high-dose fentanyl appears to be due to the combination of nifedipine and a beta-blocker, but the possibility that it may occur with nifedipine alone, with low doses of fentanyl, in other surgical procedures, or with other narcotic analgesics cannot be ruled out. In nifedipine-treated patients where surgery using high-dose fentanyl anesthesia is contemplated, the physician should be aware of these potential problems and, if the patient’s condition permits, sufficient time (at least 36 hours) should be allowed for nifedipine to be washed out of the body prior to surgery.

Increased Angina and/or Myocardial Infarction

Rarely, patients, particularly those who have severe obstructive coronary artery disease, have developed well-documented increased frequency, duration, and/or severity of angina or acute myocardial infarction upon starting nifedipine or at the time of dosage increase. The mechanism of this effect is not established.

Beta-Blocker Withdrawal

When discontinuing a beta-blocker, it is important to taper its dose, if possible, rather than stopping abruptly before beginning nifedipine. Patients recently withdrawn from beta-blockers may develop a withdrawal syndrome with increased angina, probably related to increased sensitivity to catecholamines. Initiation of nifedipine treatment will not prevent this occurrence and on occasion has been reported to increase it.

Congestive Heart Failure

Rarely, patients (usually while receiving a beta-blocker) have developed heart failure after beginning nifedipine. Patients with tight aortic stenosis may be at greater risk for such an event, as the unloading effect of nifedipine would be expected to be of less benefit to these patients, owing to their fixed impedance to flow across the aortic valve.

General
Hypotension

Because nifedipine decreases peripheral vascular resistance, careful monitoring of blood pressure during the initial administration and titration of nifedipine extended-release tablets is suggested. Close observation is especially recommended for patients already taking medications that are known to lower blood pressure (see WARNINGS).

Peripheral Edema

Mild to moderate peripheral edema occurs in a dose-dependent manner with nifedipine extended-release tablets. The placebo subtracted rate is approximately 8% at 30 mg, 12% at 60 mg and 19% at 90 mg daily. This edema is a localized phenomenon, thought to be associated with vasodilation of dependent arterioles and small blood vessels and not due to left ventricular dysfunction or generalized fluid retention. With patients whose hypertension is complicated by congestive heart failure, care should be taken to differentiate this peripheral edema from the effects of increasing left ventricular dysfunction.

Use in Cirrhotic Patients

Clearance of nifedipine is reduced and systemic exposure increased in patients with cirrhosis. It is unknown how systemic exposure may be altered in patients with moderate or severe liver impairment. Careful monitoring and dose reduction may be necessary; consider initiating therapy with the lowest dose available.

Information for Patients

Nifedipine extended-release tablets are an extended-release tablet and should be swallowed whole and taken on an empty stomach. It should not be administered with food. Do not chew, divide or crush tablets.

Laboratory Tests

Rare, usually transient, but occasionally significant elevations of enzymes such as alkaline phosphatase, CPK, LDH, SGOT and SGPT have been noted. The relationship to nifedipine therapy is uncertain in most cases, but probable in some. These laboratory abnormalities have rarely been associated with clinical symptoms; however, cholestasis with or without jaundice has been reported. A small increase (<5%) in mean alkaline phosphatase was noted in patients treated with nifedipine extended-release tablets. This was an isolated finding and it rarely resulted in values which fell outside the normal range. Rare instances of allergic hepatitis have been reported with nifedipine treatment. In controlled studies, nifedipine extended-release tablets did not adversely affect serum uric acid, glucose, cholesterol or potassium.

Nifedipine, like other calcium channel blockers, decreases platelet aggregation in vitro. Limited clinical studies have demonstrated a moderate but statistically significant decrease in platelet aggregation and increase in bleeding time in some nifedipine patients. This is thought to be a function of inhibition of calcium transport across the platelet membrane. No clinical significance for these findings has been demonstrated.

Positive direct Coombs’ test, with or without hemolytic anemia, has been reported, but a causal relationship between nifedipine administration and positivity of this laboratory test, including hemolysis, could not be determined.

Although nifedipine has been used safely in patients with renal dysfunction and has been reported to exert a beneficial effect in certain cases, rare reversible elevations in BUN and serum creatinine have been reported in patients with pre-existing chronic renal insufficiency. The relationship to nifedipine therapy is uncertain in most cases but probable in some.

Drug Interactions

Nifedipine is mainly eliminated by metabolism and is a substrate of CYP3A. Inhibitors and inducers of CYP3A can impact the exposure to nifedipine and consequently its desirable and undesirable effects. In vitro and in vivo data indicate that nifedipine can inhibit the metabolism of drugs that are substrates of CYP3A, thereby increasing the exposure to other drugs. Nifedipine is a vasodilator, and coadministration of other drugs affecting blood pressure may result in pharmacodynamic interactions.

Non-Cardiovascular Drugs

Carcinogenesis, Mutagenesis, Impairment of Fertility

Nifedipine was administered orally to rats for two years and was not shown to be carcinogenic. When given to rats prior to mating, nifedipine caused reduced fertility at a dose approximately 30 times the maximum recommended human dose. There is a literature report of reversible reduction in the ability of human sperm obtained from a limited number of infertile men taking recommended doses of nifedipine to bind to and fertilize an ovum in vitro. In vivo mutagenicity studies were negative.

Pregnancy

Nursing Mothers

Nifedipine is excreted in human milk. Nursing mothers are advised not to breastfeed their babies when taking the drug.

Pediatric Use

The safety and effectiveness of nifedipine in pediatric patients have not been established.

Geriatric Use

Although small pharmacokinetic studies have identified an increased half-life and increased Cmax and AUC (see CLINICAL PHARMACOLOGY: Pharmacokinetics and Metabolism), clinical studies of nifedipine did not include sufficient numbers of subjects aged 65 and over to determine whether they respond differently from younger subjects. Other reported clinical experience has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy.

Patients with Galactose Intolerance

Since this medicinal product contains lactose, patients with rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose-galactose malabsorption should not take this medicine.