Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2022 Publisher: Essential Pharma Ltd, 7 Egham Business Village, Crabtree Road, Egham, Surrey, TW20 8RB, UK
Verapamil is a calcium antagonist which blocks the inward movement of calcium ions in cardiac muscle cells, in smooth muscle cells of the coronary and systemic arteries and in the cells of the intracardiac conduction system. Verapamil lowers peripheral vascular resistance with no reflex tachycardia. Its efficacy in reducing both raised systolic and diastolic blood pressure is thought to be 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 antianginal properties of the drug. Because of its effect on the movement of calcium in the intracardiac conduction system, verapamil reduces automaticity, decreases conduction velocity and increases the refractory period.
Over 90% of verapamil is absorbed following administration with peak plasma concentrations occurring between 1 and 2 hours and does not appear to be affected markedly by food.
Verapamil is subject to pre-systemic hepatic metabolism with up to 80% of the dose eliminated this way. Because of rapid biotransformation of verapamil during its first pass through the portal circulation, absolute bioavailability ranges from 20–35%. Verapamil is widely distributed throughout the body with a distribution half-life of 15–30 mins. Verapamil is 90% bound to plasma proteins, mainly to albumin and µ 1 glycoprotein. The half life of verapamil after a single oral dose is between 2 and 7h. However, after repeated administration it increases to 4.5 to 12h resulting in accumulation of the drug.
Verapamil is a drug on which extensive clinical experience has been obtained. Relevant information for the prescriber is provided elsewhere in the Summary of Product Characteristics.
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