Afeditab CR

Name: Afeditab CR

Afeditab CR Overview

Nifedipine is a prescription medication used to treat chest pain. This medication belongs to a group of drugs called calcium channel blockers, which relax blood vessels, making it easier for the heart to pump blood.

Nifedipine comes in an immediate release capsule form and is taken 3 or 4 times a day, with or without food. This medication also comes in an extended release tablet form. It is taken once a day, with or without food.

Common side effects of nifedipine include swelling, headache, flushing, and nausea. Nifedipine can also cause dizziness. Do not drive or operate heavy machinery until you know how this medication will affect you.

Uses of Afeditab CR

Nifedipine is a prescription medication used to treat chest pain.

The extended release form of nifedipine, is a prescription medication used to treat chest pain and high blood pressure.

These medications may be prescribed for other uses. Ask your doctor or pharmacist for more information.

Afeditab CR Usage

Take nifedipine exactly as prescribed.

This medication comes in an immediate release capsule form and is taken 3 or 4 times a day, with or without food. Swallow whole, do not chew or crush the capsule or its contents.

This medication also comes in an extended release tablet form and is taken once a day, with or without food. Do not chew or swallow these tablets. These tablets are made with a non-absorbable shell that may be passed into the stools. This is an expected occurrence.

If you miss a dose, take the missed dose as soon as you remember. If it is almost time for the next dose, skip the missed dose and take your next dose at the regular time. Do not take two doses of nifedipine at the same time.

Afeditab CR Dosage

Take nifedipine exactly as prescribed by your doctor. Follow the directions on your prescription label carefully.

The recommended dose range for nifedipine is 10 to 60 mg three or four times a day. A total daily dose above 180 mg is not recommended.

The recommended dose range for the extended release form is 30 to 120 mg once a day. A total daily doses above 120 mg is not recommended.

  • Dose adjustments may be done based on liver function, kidney function, physical activity level, frequency of chest pains, response to medication, and the use of other medications.

If discontinuation of nifedipine is necessary, the dose should be decreased gradually with close physician supervision.

Commonly used brand name(s)

In the U.S.

  • Adalat CC
  • Afeditab CR
  • Nifediac CC
  • Nifedical XL
  • Procardia
  • Procardia XL

Available Dosage Forms:

  • Capsule, Liquid Filled
  • Tablet, Extended Release
  • Tablet
  • Capsule

Therapeutic Class: Cardiovascular Agent

Pharmacologic Class: Calcium Channel Blocker

Chemical Class: Dihydropyridine

Before Using Afeditab CR

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:

Allergies

Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.

Pediatric

Appropriate studies have not been performed on the relationship of age to the effects of nifedipine in the pediatric population. Safety and efficacy have not been established.

Geriatric

Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of nifedipine in the elderly. However, elderly patients are more likely to have age-related kidney, liver, or heart problems which may require caution and an adjustment in the dose for patients receiving nifedipine.

Pregnancy

Pregnancy Category Explanation
All Trimesters C Animal studies have shown an adverse effect and there are no adequate studies in pregnant women OR no animal studies have been conducted and there are no adequate studies in pregnant women.

Breast Feeding

Studies in women suggest that this medication poses minimal risk to the infant when used during breastfeeding.

Interactions with Medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Amiodarone
  • Amobarbital
  • Aprobarbital
  • Armodafinil
  • Atazanavir
  • Boceprevir
  • Bosentan
  • Butabarbital
  • Butalbital
  • Carbamazepine
  • Ceritinib
  • Clarithromycin
  • Clobazam
  • Clopidogrel
  • Cobicistat
  • Conivaptan
  • Dantrolene
  • Dexamethasone
  • Digoxin
  • Efavirenz
  • Enzalutamide
  • Etravirine
  • Fentanyl
  • Fosphenytoin
  • Idelalisib
  • Itraconazole
  • Ketoconazole
  • Lacosamide
  • Lopinavir
  • Mephobarbital
  • Methohexital
  • Mibefradil
  • Modafinil
  • Nafcillin
  • Nefazodone
  • Nelfinavir
  • Netupitant
  • Nevirapine
  • Oxcarbazepine
  • Pentobarbital
  • Phenobarbital
  • Phenytoin
  • Pioglitazone
  • Posaconazole
  • Prednisone
  • Primidone
  • Rifabutin
  • Rifampin
  • Rifapentine
  • Ritonavir
  • Rufinamide
  • Saquinavir
  • Secobarbital
  • St John's Wort
  • Telaprevir
  • Telithromycin
  • Thiopental
  • Topiramate
  • Voriconazole

Using this medicine with any of the following medicines may cause an increased risk of certain side effects, but using both drugs may be the best treatment for you. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Cimetidine
  • Dalfopristin
  • Doxazosin
  • Ginkgo
  • Ginseng
  • Indinavir
  • Magnesium
  • Micafungin
  • Quinidine
  • Quinupristin
  • Tacrolimus
  • Vincristine
  • Vincristine Sulfate Liposome

Interactions with Food/Tobacco/Alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following may cause an increased risk of certain side effects but may be unavoidable in some cases. If used together, your doctor may change the dose or how often you use this medicine, or give you special instructions about the use of food, alcohol, or tobacco.

  • Grapefruit Juice

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Aortic stenosis (narrowing of a valve in your heart) or
  • Bowel blockage, severe or
  • Congestive heart failure or
  • Coronary artery disease or
  • Heart attack or
  • Hypotension (low blood pressure)—Use with caution. May increase risk of serious side effects.
  • Cardiogenic shock (shock caused by heart attack)—Should not be used in patients with these conditions.
  • Galactose intolerance (rare hereditary problem) or
  • Glucose-galactose malabsorption (rare hereditary problem) or
  • Lapp lactase deficiency (rare hereditary problem)—The extended release tablet form of this medicine contains lactose (milk sugar), and should not be given to patients with these conditions.
  • Kidney problems or
  • Liver problems (including cirrhosis)—Use with caution. The effects of nifedipine may be increased because of the slower removal of the medicine from the body.

Proper Use of nifedipine

This section provides information on the proper use of a number of products that contain nifedipine. It may not be specific to Afeditab CR. Please read with care.

In addition to the use of this medicine, treatment for your high blood pressure may include weight control and changes in the types of foods you eat, especially foods high in sodium (salt). Your doctor will tell you which of these are most important for you. You should check with your doctor before changing your diet.

Many patients who have high blood pressure will not notice any signs of the problem. In fact, many may feel normal. It is very important that you take your medicine exactly as directed and that you keep your appointments with your doctor even if you feel well.

Remember that this medicine will not cure your high blood pressure, but it does help control it. You must continue to take it as directed if you expect to lower your blood pressure and keep it down. You may have to take high blood pressure medicine for the rest of your life. If high blood pressure is not treated, it can cause serious problems such as heart failure, blood vessel disease, stroke, or kidney disease.

Swallow the extended release tablet whole. Do not break, crush, or chew it. It is best to take this tablet on an empty stomach.

If you are taking the extended-release tablets, part of the tablet may pass into your stool after your body has absorbed the medicine. This is normal and nothing to worry about.

Dosing

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For treatment of chest pain or high blood pressure:
    • For oral dosage form (capsules):
      • Adults—At first, 10 milligrams (mg) three times a day. Your doctor may increase your dose as needed.
      • Children—Use and dose must be determined by your doctor.
    • For oral dosage form (extended-release tablets):
      • Adults—At first, 30 or 60 milligrams (mg) once a day. Your doctor may increase your dose as needed. However, the dose is usually not more than 90 mg once a day.
      • Children—Use and dose must be determined by your doctor.

Missed Dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage

Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Precautions While Using Afeditab CR

It is very important that your doctor check your progress at regular visits to make sure that this medicine is working properly and to check for unwanted effects.

You should not use this medicine if you are also taking certain other medications such as carbamazepine (Tegretol®), phenobarbital (Luminal®), phenytoin (Dilantin®), rifabutin (Mycobutin®), rifampin (Rifadin®, Rimactane®), or St. John's Wort. Using these medicines together can cause serious problems. Make sure your doctor knows all of the medications you are taking.

Dizziness, lightheadedness, or fainting may occur, especially when you get up suddenly from a lying or sitting position. These symptoms are more likely to occur when you begin taking this medicine, or when the dose is increased.

This medicine may cause fluid retention (edema) in some patients. Tell your doctor right away if you have bloating or swelling of the face, arms, hands, lower legs, or feet; tingling of the hands or feet; or unusual weight gain or loss.

Do not stop taking this medicine without first checking with your doctor. Your doctor may want you to gradually reduce the amount you are using before stopping completely.

Make sure any doctor or dentist who treats you knows that you are using this medicine. You may need to stop using this medicine several days before having surgery or medical tests. This medicine may affect the results of certain medical tests.

Grapefruits and grapefruit juice may increase the effects of nifedipine by increasing the amount of this medicine in your body. You should not eat grapefruit or drink grapefruit juice while you taking this medicine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

Precautions

General - Hypotension:

Because nifedipine decreases peripheral vascular resistance, careful monitoring of blood pressure during the initial administration and titration of Afeditab® CR 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 Afeditab® CR. 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.

Information for Patients:

Afeditab® CR is 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.

Patients should be advised that empty matrix “ghosts” (tablets) may pass via colostomy or in the stool, and that this is of no concern since the active medication has already been absorbed.

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:

Beta-adrenergic blocking agents (See WARNINGS.)
Nifedipine is mainly eliminated by metabolism and is a substrate of CYP3A. Inhibitors and inducers of CYP3A4 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 co-administration of other drugs affecting blood pressure may result in pharmacodynamic interactions.

Cardiovascular Drugs
Antiarrhythmics
Quinidine: Quinidine is a substrate of CYP3A and has been shown to inhibit CYP3A in vitro. Co-administration of multiple doses of quinidine sulfate, 200 mg t.i.d., and nifedipine, 20 mg t.i.d., increased Cmax and AUC of nifedipine in healthy volunteers by factors of 2.30 and 1.37, respectively. The heart rate in the initial interval after drug administration was increased by up to 17.9 beats/minute. The exposure to quinidine was not importantly changed in the presence of nifedipine. Monitoring of heart rate and adjustment of the nifedipine dose, if necessary, are recommended when quinidine is added to a treatment with nifedipine.

Flecainide: There has been too little experience with the co-administration of TAMBOCOR with nifedipine to recommend concomitant use.

Calcium Channel Blockers
Diltiazem: Pre-treatment of healthy volunteers with 30 mg or 90 mg t.i.d. diltiazem p.o. increased the AUC of nifedipine after a single dose of 20 mg nifedipine by factors of 2.2 and 3.1, respectively. The corresponding Cmax values of nifedipine increased by factors of 2.0 and 1.7, respectively. Caution should be exercised when co-administering diltiazem and nifedipine and a reduction of the dose of nifedipine should be considered.

Verapamil: Verapamil, a CYP3A inhibitor, can inhibit the metabolism of nifedipine and increase the exposure to nifedipine during concomitant therapy. Blood pressure should be monitored and reduction of the dose of nifedipine considered.

ACE Inhibitors
Benazepril: In healthy volunteers receiving single dose of 20 mg nifedipine ER and benazepril 20 mg, the plasma concentrations of benazeprilat and nifedipine in the presence and absence of each other were not statistically significantly different. A hypotensive effect was only seen after co-administration of the two drugs. The tachycardic effect of nifedipine was attenuated in the presence of benazepril.

Angiotensin-II Blockers
Irbesartan:In vitro studies show significant inhibition of the formation of oxidized irbesartan metabolites by nifedipine. However, in clinical studies, concomitant nifedipine had no effect on irbesartan pharmacokinetics.

Candesartan: No significant drug interaction has been reported in studies with candesartan cilexitil given together with nifedipine. Because candesartan is not significantly metabolized by the cytochrome P450 system and at therapeutic concentrations has no effect on cytochrome P450 enzymes, interactions with drugs that inhibit or are metabolized by those enzymes would not be expected.

Beta-blockers
Nifedipine extended-release tablets was well tolerated when administered in combination with beta-blockers in 187 hypertensive patients in a placebo-controlled clinical trial. However, there have been occasional literature reports suggesting that the combination of nifedipine and beta-adrenergic blocking drugs may increase the likelihood of congestive heart failure, severe hypotension or exacerbation of angina in patients with cardiovascular disease. Clinical monitoring is recommended and a dose adjustment of nifedipine should be considered.

Timolol: Hypotension is more likely to occur if dihydropryridine calcium antagonists such as nifedipine are co-administered with timolol.

Central Alpha1-Blockers
Doxazosin: Healthy volunteers participating in a multiple dose doxazosin-nifedipine interaction study received 2 mg doxazosin q.d. alone or combined with 20 mg nifedipine ER b.i.d. Co-administration of nifedipine resulted in a decrease in AUC and Cmax of doxazosin to 83% and 86% of the values in the absence of nifedipine, respectively. In the presence of doxazosin, AUC and Cmax of nifedipine were increased by factors of 1.13 and 1.23, respectively. Compared to nifedipine monotherapy, blood pressure was lower in the presence of doxazosin. Blood pressure should be monitored when doxazosin is co-administered with nifedipine, and dose reduction of nifedipine considered.

Digitalis
Digoxin: Since there have been isolated reports of patients with elevated digoxin levels, and there is a possible interaction between digoxin and nifedipine, it is recommended that digoxin levels be monitored when initiating, adjusting and discontinuing nifedipine extended-release tablets to avoid possible over- or under-digitalization.

Antithrombotics
Coumarins: There have been rare reports of increased prothrombin time in patients taking coumarin anticoagulants to whom nifedipine was administered. However, the relationship to nifedipine therapy is uncertain.

Platelet Aggregation Inhibitors
Clopidogrel: No clinically significant pharmacodynamic interactions were observed when clopidrogrel was co-administered with nifedipine.

Tirofiban: Co-administration of nifedipine did not alter the exposure to tirofiban importantly.

Non-Cardiovascular Drugs
Antifungal Drugs
Ketoconazole, itraconazole and fluconazole are CYP3A inhibitors and can inhibit the metabolism of nifedipine and increase the exposure to nifedipine during concomitant therapy. Blood pressure should be monitored and a dose reduction of nifedipine considered.

Antisecretory Drugs
Omeprazole: In healthy volunteers receiving a single dose of 10 mg nifedipine, AUC and Cmax of nifedipine after pretreatment with omeprazole 20 mg q.d. for 8 days were 1.26 and 0.87 times those after pre-treatment with placebo. Pretreatment with or co-administration of omeprazole did not impact the effect of nifedipine on blood pressure or heart rate. The impact of omeprazole on nifedipine is not likely to be of clinical relevance.

Pantoprazole: In healthy volunteers the exposure to neither drug was changed significantly in the presence of the other drug.

Ranitidine: Five studies in healthy volunteers investigated the impact of multiple ranitidine doses on the single or multiple dose pharmacokinetics of nifedipine. Two studies investigated the impact of coadministered ranitidine on blood pressure in hypertensive subjects on nifedipine. Co-administration of ranitidine did not have relevant effects on the exposure to nifedipine that affected the blood pressure or heart rate in normotensive or hypertensive subjects.

Cimetidine: Five studies in healthy volunteers investigated the impact of multiple cimetidine doses on the single or multiple dose pharmacokinetics of nifedipine. Two studies investigated the impact of coadministered cimetidine on blood pressure in hypertensive subjects on nifedipine.

In normotensive subjects receiving single doses of 10 mg or multiple doses of up to 20 mg nifedipine t.i.d. alone or together with cimetidine up to 1000 mg/day, the AUC values of nifedipine in the presence of cimetidine were between 1.52 and 2.01 times those in the absence of cimetidine. The Cmax values of nifedipine in the presence of cimetidine were increased by factors ranging between 1.60 and 2.02. The increase in exposure to nifedipine by cimetidine was accompanied by relevant changes in blood pressure or heart rate in normotensive subjects. Hypertensive subjects receiving 10 mg q.d. nifedipine alone or in combination with cimetidine 1000 mg q.d. also experienced relevant changes in blood pressure when cimetidine was added to nifedipine. The interaction between cimetidine and nifedipine is of clinical relevance and blood pressure should be monitored and a reduction of the dose of nifedipine considered.

Antibacterial Drugs
Quinupristin/Dalfopristin:In vitro drug interaction studies have demonstrated that quinupristin/dalfopristin significantly inhibits the CYP3A metabolism of nifedipine. Concomitant administration of quinupristin/dalfopristin and nifedipine (repeated oral dose) in healthy volunteers increased AUC and Cmax for nifedipine by factors of 1.44 and 1.18, respectively, compared to nifedipine monotherapy. Upon co-administration of quinupristin/dalfopristin with nifedipine, blood pressure should be monitored and a reduction of the dose of nifedipine considered.

Erythromycin: Erythromycin, a CYP3A inhibitor, can inhibit the metabolism of nifedipine and increase the exposure to nifedipine during concomitant therapy. Blood pressure should be monitored and reduction of the dose of nifedipine considered.

Antitubercular Drugs
Rifampin: Pretreatment of healthy volunteers with 600 mg/day rifampin p.o. decreased the exposure to oral nifedipine (20 μg/kg) to 13%. The exposure to intravenous nifedipine by the same rifampin treatment was decreased to 70%. Dose adjustment of nifedipine may be necessary if nifedipine is co-administered with rifampin.

Rifapentine: Rifapentine, as an inducer of CYP3A4, can decrease the exposure to nifedipine. A dose adjustment of nifedipine when co-administered with rifapentine should be considered.

Antiviral Drugs
Amprenavir, atanazavir, delavirine, fosamprinavir, indinavir, nelfinavir and ritonavir, as CYP3A inhibitors, can inhibit the metabolism of nifedipine and increase the exposure to nifedipine. Caution is warranted and clinical monitoring of patients recommended.

CNS Drugs
Nefazodone, a CYP3A inhibitor, can inhibit the metabolism of nifedipine and increase the exposure to nifedipine during concomitant therapy. Blood pressure should be monitored and a reduction of the dose of nifedipine considered.

Valproic acid may increase the exposure to nifedipine during concomitant therapy. Blood pressure should be monitored and a dose reduction of nifedipine considered.

Phenytoin: Nifedipine is metabolized by CYP3A4. Co-administration of nifedipine 10 mg capsule and 60 mg nifedipine coat-core tablet with phenytoin, an inducer of CYP3A4, lowered the AUC and Cmax of nifedipine by approximately 70%. When using nifedipine with phenytoin, the clinical response to nifedipine should be monitored and its dose adjusted if necessary.

Phenobarbitone and carbamazepine as inducers of CYP3A can decrease the exposure to nifedipine. Dose adjustment of nifedipine may be necessary if phenobarbitone, carbamazepine or phenytoin is coadministered.

Antiemetic Drugs
Dolasetron: In patients taking dolasetron by the oral or intravenous route and nifedipine, no effect was shown on the clearance of hydrodolasetron.

Immunosuppressive Drugs
Tacrolimus: Nifedipine has been shown to inhibit the metabolism of tacrolimus in vitro. Transplant patients on tacrolimus and nifedipine required from 26% to 38% smaller doses than patients not receiving nifedipine. Nifedipine can increase the exposure to tacrolimus. When nifedipine is co-administered with tacrolimus the blood concentrations of tacrolimus should be monitored and a reduction of the dose of tacrolimus considered.

Sirolimus: A single 60 mg dose of nifedipine and a single 10 mg dose of sirolimus oral solution were administered to 24 healthy volunteers. Clinically significant pharmacokinetic drug interactions were not observed.

Glucose Lowering Drugs
Pioglitazone: Co-administration of pioglitazone for 7 days with 30 mg nifedipine ER administered orally q.d. for 4 days to male and female volunteers resulted in least square mean (90% CI) values for unchanged nifedipine of 0.83 (0.73-0.95) for Cmax and 0.88 (0.80-0.96) for AUC relative to nifedipine monotherapy. In view of the high variability of nifedipine pharmacokinetics, the clinical significance of this finding is unknown.

Rosiglitazone: Co-administration of rosiglitazone (4 mg b.i.d.) was shown to have no clinically relevant effect on the pharmacokinetics of nifedipine.

Metformin: A single dose metformin-nifedipine interaction study in normal healthy volunteers demonstrated that co-administration of nifedipine increased plasma metformin Cmax and AUC by 20% and 9%, respectively, and increased the amount of metformin excreted in urine. Tmax and half-life were unaffected. Nifedipine appears to enhance the absorption of metformin.

Miglitol: No effect of miglitol was observed on the pharmacokinetics and pharmacodynamics of nifedipine.

Repaglinide: Co-administration of 10 mg nifedipine with a single dose of 2 mg repaglinide (after 4 days nifedipine 10 mg t.i.d. and repaglinide 2 mg t.i.d.) resulted in unchanged AUC and Cmax values for both drugs.

Acarbose: Nifedipine tends to produce hyperglycemia and may lead to loss of glucose control. If nifedipine is co-administered with acarbose, blood glucose levels should be monitored carefully and a dose adjustment of nifedipine considered.

Drugs Interfering with Food Absorption
Orlistat: In 17 normal-weight subjects receiving orlistat 120 mg t.i.d. for 6 days, orlistat did not alter the bioavailability of 60 mg nifedipine (extended-release tablets).

Dietary Supplements
Grapefruit Juice: In healthy volunteers, a single dose co-administration of 250 mL double strength grapefruit juice with 10 mg nifedipine increased AUC and Cmax by factors of 1.35 and 1.13, respectively. Ingestion of repeated doses of grapefruit juice (5 x 200 mL in 12 hours) after administration of 20 mg nifedipine ER increased AUC and Cmax of nifedipine by a factor of 2.0. Grapefruit juice should be avoided by patients on nifedipine. The intake of grapefruit juice should be stopped at least 3 days prior to initiating patients on nifedipine.

Herbals
St. John’s Wort: Is an inducer of CYP3A4 and may decrease the exposure to nifedipine. Dose adjustment of nifedipine may be necessary if St. John’s Wort is co-administered.

CYP2D6 Probe Drug
Debrisoquine: In healthy volunteers, pretreatment with nifedipine 20 mg t.i.d. for 5 days did not change the metabolic ratio of hydroxydebrisoquine to debrisoquine measured in urine after a single dose of 10 mg debrisoquine. Thus, it is improbable that nifedipine inhibits in vivo the metabolism of other drugs that are substrates of CYP2D6.

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:

Pregnancy Category C. In rodents, rabbits and monkeys, nifedipine has been shown to have a variety of embryotoxic, placentotoxic and fetotoxic effects, including stunted fetuses (rats, mice and rabbits), digital anomalies (rats and rabbits), rib deformities (mice), cleft palate (mice), small placentas and underdeveloped chorionic villi (monkeys), embryonic and fetal deaths (rats, mice and rabbits), prolonged pregnancy (rats; not evaluated in other species), and decreased neonatal survival (rats; not evaluated in other species). On a mg/kg or mg/m2 basis, some of the doses associated with these various effects are higher than the maximum recommended human dose and some are lower, but all are within an order of magnitude of it.

The digital anomalies seen in nifedipine-exposed rabbit pups are strikingly similar to those seen in pups exposed to phenytoin, and these are in turn similar to the phalangeal deformities that are the most common malformation seen in human children with in utero exposure to phenytoin.

There are no adequate and well-controlled studies in pregnant women. Nifedipine should generally be avoided during pregnancy and used only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers:

Nifedipine is excreted in human milk. Therefore, a decision should be made to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother.

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.

Overdosage

Experience with nifedipine overdosage is limited. Symptoms associated with severe nifedipine overdosage include loss of consciousness, drop in blood pressure, heart rhythm disturbances, metabolic acidosis, hypoxia, cardiogenic shock with pulmonary edema. Generally, overdosage with nifedipine leading to pronounced hypotension calls for active cardiovascular support including monitoring of cardiovascular and respiratory function, elevation of extremities, judicious use of calcium infusion, pressor agents and fluids. Clearance of nifedipine would be expected to be prolonged in patients with impaired liver function. Since nifedipine is highly protein bound, dialysis is not likely to be of any benefit; however, plasmapheresis may be beneficial.

There has been one reported case of massive overdosage with tablets of another extended-release formulation of nifedipine. The main effects of ingestion of approximately 4800 mg of nifedipine in a young man attempting suicide as a result of cocaine-induced depression was initial dizziness, palpitations, flushing, and nervousness.Within several hours of ingestion, nausea, vomiting, and generalized edema developed. No significant hypotension was apparent at presentation, 18 hours post ingestion. Blood chemistry abnormalities consisted of a mild, transient elevation of serum creatinine, and modest elevations of LDH and CPK, but normal SGOT. Vital signs remained stable, no electrocardiographic abnormalities were noted and renal function returned to normal within 24 to 48 hours with routine supportive measures alone. No prolonged sequelae were observed.

The effect of a single 900 mg ingestion of nifedipine capsules in a depressed anginal patient on tricyclic antidepressants was loss of consciousness within 30 minutes of ingestion, and profound hypotension, which responded to calcium infusion, pressor agents, and fluid replacement. A variety of ECG abnormalities were seen in this patient with a history of bundle branch block, including sinus bradycardia and varying degrees of AV block. These dictated the prophylactic placement of a temporary ventricular pacemaker, but otherwise resolved spontaneously. Significant hyperglycemia was seen initially in this patient, but plasma glucose levels rapidly normalized without further treatment.

A young hypertensive patient with advanced renal failure ingested 280 mg of nifedipine capsules at one time, with resulting marked hypotension responding to calcium infusion and fluids. No AV conduction abnormalities, arrhythmias, or pronounced changes in heart rate were noted, nor was there any further deterioration in renal function.

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