Nifedipine

Nifedipine(中文:硝苯地平) is a dihydropyridine calcium-channel blocker. It is used in the management of hypertension and angina.

Pronunciation

Nifedipine 20mg (ADALAT RETARD 20mg)

Nifedipine 5mg (ADALAT RETARD 5mg)

HA Code:	NIFE03
Generic Name:	Nifedipine
Brand Name:	ADALAT RETARD
Class:	Cardiovascular Drug
Subclass:	Calcium-channel Blocker, CCB
Legal Classification:	P1S1S3

Drug Names

Generic Name 藥物化學名稱	HA Code 藥物代碼	Legal Classification法律藥物分類	Brand Name 品牌名稱
Nifedipine SR Tablet 20mg	NIFE03	P1S1S3	ADALAT RETARD TABLET

Mechanism of Action:

Nifedipine relaxes and widens blood vessels. It does this by blocking calcium going into muscles in the heart and blood vessels. Muscles need calcium to contract, so when you block the calcium, it makes the muscle cells relax. This lowers your blood pressure and makes it easier for your heart to pump blood around your body.

In angina, nifedipine works by improving the blood and oxygen supply to your heart. Angina is chest pain that comes on when not enough blood gets to the muscles of the heart. This usually happens because the arteries going to the heart become hardened and narrowed.

Route of Administration:

Nifedipine is given orally in a sustained-release formulation.

Dosage

Agina

• BY MOUTH
• Adult: 10 mg twice daily, adjusted according to response to 40 mg twice daily.

Hypertension

• BY MOUTH
• Adult: 10 mg twice daily, adjusted according to response to 40 mg twice daily.

Side Effects

The following definitions of frequencies are used:

Very common ≥ 1/10

Common ≥ 1/100 to < 1/10

Uncommon ≥ 1/1,000 to < 1/100

Rare ≥ 1/10,000 to < 1/1,000

Very rare < 1/10,000

System Organ Class	Frequency	Adverse reactions
Nervous system disorder	Common	Headache
Cardiac disorders	UnCommon	Tachycardia, palpitations
Vascular disorders	Common	Flushing
Gastro-intestinal disorders	UnCommon	Abdominal pain, nausea, constipation
	Very rare	Gum hyperplasia
General disorders	Common	Peripheral oedema

Pharmacokinetics

Absorption

After oral administration nifedipine is rapidly and almost completely absorbed. The systemic availability of orally administered nifedipine is 45 – 56% owing to a first pass effect. Maximum plasma and serum concentrations are reached at 1.5 to 4.2 hours with nifedipine. Simultaneous food intake leads to delayed, but not reduced absorption.

Distribution

Nifedipine is about 95% bound to plasma protein (albumin).

Metabolism

After oral administration, nifedipine is metabolized in the gut wall and in the liver.

Nifedipine is excreted in the form of its metabolites predominantly via the kidney and about 5 – 15% via the bile in the faeces.

Elimination

The terminal elimination half-life is 6 – 11 hours because of delayed absorption. No accumulation of the substance after the usual dose was reported during long-term treatment.

How long does nifedipine take to work?

Nifedipine (Adalat Retard) tablets have extended-release properties, so they absorb in the body slowly over time and can take up to 4 hours to reach its “peak” effect.

Drug Management

Drug Interaction:

Nifedipine is metabolized in the liver by cytochrome P450 3A4 (CYP3A4). Drugs that are known to either inhibit or to induce this enzyme system may therefore alter the first pass (after oral administration) or the clearance of nifedipine.

The extent as well as the duration of interactions should be taken into account when administering nifedipine together with the following drugs:

Rifampicin : Rifampicin strongly induces the cytochrome P450 3A4 system. Upon coadministration with rifampicin, the bioavailability of nifedipine is distinctly reduced and thus its efficacy weakened. The use of nifedipine in combination with rifampicin is therefore contraindicated

Interactions leading to increased plasma concentration of nifedipine

CYP3A4 enzyme inhibitors have been shown to cause an increase in nifedipine plasma concentrations. In case of clinically significant adverse events due to elevated nifedipine exposure when combined with strong CYP3A4 inhibitors, adjustment of nifedipine dose and/or discontinuation of the CYP3A4 inhibitor should be considered.

Examples:

- Cimetidine

- Erythromycin

- Itraconazole

- Ketoconazole

- Certain flavonoids present in grapefruit juice

Nifedipine tablets should not be taken together with grapefruit juice.

Interactions leading to decreased plasma concentration of nifedipine

Enzyme inducers of the cytochrome P450 3A4 system have been shown to cause a decrease in plasma concentrations of nifedipine. In case of lack of efficacy due to decreased nifedipine exposure when combined with potent inducers of CYP3A4, adjustment of nifedipine dose and/or discontinuation of the CYP3A4 inducer should be considered.

Examples:

- Phenytoin

- Carbamazepine

- Rifampicin

- Barbiturates

- Hypericum perforatum (Saint John's wort)

Additional interactions

The simultaneous administration of nifedipine and digoxin may lead to reduced digoxin clearance and, hence, an increase in the plasma concentrations of digoxin. The patient should therefore be checked for symptoms of digoxin overdosage as a precaution and, if necessary, the glycoside dose should be reduced taking account of the plasma concentration of digoxin.

Contraindication:

Cardiac outflow obstruction

• Significant cardiac valvular obstruction (e.g. aortic stenosis)
• Uncontrolled heart failure
• Unstable angina
• Within 1 month of myocardial infarction

Pregnancy: avoid

FAQ

How should I take the tablet?

Swallow the tablet whole with a drink of water. Do not crush the tablet.

What should I avoid while taking?

Avoid eating grapefruit or drinking grapefruit juice while taking amlodipine. Grapefruit juice can increase felodipine in your body and make side effects worse, such as flushing or getting headaches.

What happen if I miss a dose?

If you forget to take a dose and you usually take nifedipine twice a day – take it as soon as you remember unless it is less than 4 hours until your next dose. In this case leave out the missed dose and take your next dose at the usual time. Never take 2 doses to make up for a forgotten one.