Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2019 Publisher: Accord-UK Ltd (Trading style: Accord), Whiddon Valley, Barnstaple, Devon, EX32 8NS
Pharmacotherapeutic group: Selective calcium channel blockers with direct cardiac effects, phenylalkylamine derivatives
ATC code: C08DA01
Verapamil hydrochloride is a calcium channel blocker and is classified as a class IV anti-arrhythmic agent.
Verapamil inhibits the entry of calcium into smooth muscle cells of the systemic and coronary arteries and in the cells of cardiac muscle and the intracardiac conduction system.
Verapamil lowers peripheral vascular resistance with little or no reflex tachycardia. Its efficacy in reducing both raised systolic and diastolic blood pressure is thought to be primarily due to this mode of action.
The decrease in systemic and coronary vascular resistance and the sparing effect on intracellular oxygen consumption appear to explain the anti-anginal properties of the product.
Due to the effect on the movement of calcium in the intracardiac conduction system, verapamil reduces automaticity, decreases conduction velocity and increases the refractory period.
Verapamil is approximately 90% absorbed from the gastrointestinal tract.
Verapamil acts within 1-2 hours after oral administration with a peak plasma concentration after 1-2 hours. There is considerable interindividual variation in plasma concentrations. Verapamil is about 90% bound to plasma proteins.
Verapamil is subject to very considerable first-pass metabolism in the liver and the bioavailability is only about 20%. It is extensively metabolised in the liver to at least 12 metabolites of which norverapamil has been shown to have some activity.
Verapamil exhibits bi- or tri-phasic elimination kinetics and is reported to have a terminal plasma half-life of 2-8 hours following a single oral dose. After repeated oral doses this increases to 4.5-12 hours. About 70% of a dose is excreted by the kidneys in the form of its metabolites but about 16% is also excreted in the bile into the faeces. Less than 4% is excreted unchanged.
Verapamil crosses the placenta and is excreted in breast milk (see section 4.6).
Not applicable.
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