Amlodipine is a dihydropyridine calcium – channel blocker. It is a peripheral and coronary vasodilator, but, unlike the calcium – channel blockers verapamil or diltiazem, has little or no effect on cardiac conduction and negative inotropic activity is rarely seen at therapeutic doses. Administration of Amlodipine results primarily in vasodilatation, with reduced peripheral resistance, blood pressure, and afterload, increased coronary blood flow, and a reflex increase in heart rate. This in turn results in an increase in myocardial oxygen supply and cardiac output.
Amlodipine is well absorbed following oral administration with peak blood concentrations occurring after 6 to 12 hours. The bioavailability varies but is usually about 60 to 65%. Amlodipine is reported to be about 97.5% bound to plasma proteins. It has a prolonged terminal elimination half-life of 35 to 50 hours and steady-state plasma concentrations are not achieved until after 7 to 8 days of administration. Amlodipine is extensively metabolised in the liver; metabolites are mostly excreted in urine together with less than 10% of a dose as unchanged drug.
It is used in the management of hypertension and angina pectoris.
DOSAGE AND ADMINISTRATION:
Hypertension and stable angina pectoris:
The usual dose is 5mg once daily. If necessary, this may be increased to 10mg once daily.