Calcium Channel Blockers

Introduction

• Definition — Calcium channel blockers (CCBs) — also called Ca²⁺ entry blockers / Ca²⁺ antagonists — inhibit Ca²⁺ influx through voltage-gated L-type ("slow") Ca²⁺ channels in vascular smooth muscle and cardiac myocytes, producing vasodilatation and negative cardiac actions.
• Two core actions — All CCBs share two pharmacodynamic actions — (i) relaxation of vascular (arteriolar) smooth muscle and (ii) negative inotropic, chronotropic & dromotropic effects on the heart. The ratio of these two effects differs by chemical class and is the single most important organising concept of the topic.
• Historical anchor — Fleckenstein (1960s) introduced the concept of blocking Ca²⁺ entry into myocytes; verapamil (a papaverine congener, 1962) was the first clinical CCB — a coronary vasodilator with additional negative inotropic/chronotropic effects.
• Clinical relevance — Now first-line in hypertension and angina (all classes) and in supraventricular arrhythmias (non-DHPs only); usable where β-blockers are contraindicated (asthma/COPD, peripheral vascular disease).