Norvasc (Amlodipine). Dosage, Side Effects, Interactions
Amlodipine is a calcium channel blocker and is used to treat heart diseases such as high blood pressure (hypertension), coronary artery disease (CHD) or angina pectoris.
Drugs with the calcium channel blocker amlodipine are used due to their vasodilating (dilating) and blood pressure-lowering effect in the treatment of hypertension (high blood pressure), in the treatment of coronary heart disease and chronically stable angina pectoris and vasospastic (Prinzmetal’s) angina. Normally, the active ingredient is taken once a day in the form of tablets.
Amlodipine is a dihydropyridine-type L-type calcium channel blocker and inhibits the influx of calcium ions into cardiac muscle cells and vascular smooth muscle cells. The effect consists of:
- Relaxation of vascular smooth muscle
- Expansion of peripheral arterioles (afterload reduction)
- Dilatation of coronary arteries and arterioles (myocardial oxygenation increases).
The widening of the peripheral arterioles lowers the peripheral resistance (afterload) against which the heart must work. The heart rate remains stable, which reduces myocardial energy expenditure and oxygen demand. These mechanisms result in the heart being relieved.
Dilatation of the coronary arteries and arterioles occurs in both the physiological and ischemic ranges. This improves myocardial oxygenation during coronary artery spasms associated with Prinzmetal’s or vasospastic angina.
Amlodipine is usually well absorbed and is independent of food intake. Peak concentrations are reached after 6 to 12 hours. The absolute bioavailability in humans is 64-80%. The volume of distribution is approximately 21 l/kg. In vitro, approximately 97.5% of circulating amlodipine is bound to plasma proteins.
The half-life is very long at 30 to 50 hours. This allows for once daily dosing. The active substance is largely metabolised in the liver to inactive metabolites. 10% of the drug is excreted unchanged and 60% in the form of metabolites in the urine.
Dosage of Norvasc (Amlodipine)
Amlodipine is taken orally. The dosage is 5 mg once a day, up to a maximum of 10 mg once a day. The dose should be increased with caution, especially in elderly patients.
Side effects of Norvasc (Amlodipine)
Side effects that occur frequently (≥1/100 to <1/10) include:
- Drowsiness, dizziness, headache
- visual disturbances
- reddening of the skin and a feeling of warmth
- Abdominal pain, nausea, dyspepsia, altered bowel habits
- ankle swelling
- muscle cramps
- feeling weak.
All other side effects can be found in the information for professionals.
Amlodipine is metabolised by CYP3A4 , therefore concomitant use of CYP3A4 inhibitors such as e.g.:
- protease inhibitors
- azole antifungals
may lead to increased plasma levels of amlodipine.
Conversely, since CYP3A4 inducers such as B. rifampicin or St. John’s wort , which can reduce plasma levels of amlodipine, they should be used with caution.
Amlodipine may increase tacrolimus plasma levels and the dose may need to be adjusted.
The dose of simvastatin should be restricted to 20 mg daily during amlodipine therapy since amlodipine increases simvastatin exposure by approximately 77%.
Amlodipine must not be used in:
- Hypersensitivity to dihydropyridines and/or amlodipine
- severe hypotension
- shock (including cardiogenic shock)
- Obstruction of the left ventricular outflow tract (such as in high-grade aortic stenosis )
- Hemodynamically unstable heart failure after acute myocardial infarction .
The use of amlodipine during pregnancy is only recommended if no safer therapeutic alternatives are available, since reproductive toxicity has been observed in animal studies at high doses.
Amlodipine passes into breast milk in nursing mothers. It is not known whether amlodipine has an effect on infants and should therefore only be used during breast-feeding after careful benefit-risk assessment and if clearly necessary.
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