Verapamil

Verapamil, one member of a group of structurally and pharmacologically heterogeneous drugs that decrease calcium flux across the plasma membrane, is an important drug both as an experimental substance useful in furthering our understanding of excitation-contraction and secretion coupling and as a therapeutic agent. The major effects of verapamil include depression of AV conduction, reduction of systemic arterial resistance, and a reduction in the force of left ventricular contraction. After single intravenous or oral doses of verapamil, the hemodynamic effects do not last as long as do the effects on AV conduction, but little is known regarding the time course of the effects of chronic dosing. The principal therapeutic use of verapamil is to terminate attacks of paroxysmal supraventricular tachycardia and to augment the effect of digitalis on AV conduction in patients with atrial fibrillation when digitalis alone is unsuccessful. In exercise-induced angina the drug is a useful alternative to beta adrenergic antagonist drugs. In angina attributed to coronary spasm the drug appears promising. No comparative trials have been published comparing verapamil with nifedipine. Of the two, nifedipine would seem to be the preferred drug in variant angina, at present, because it does not affect AV conduction and more studies have been published establishing it as a useful agent to reduce the number and severity of attacks. Verapamil has been shown to be a useful alternative to beta adrenergic antagonist drugs in the obstructive form of hypertrophic cardiomyopathy. Although verapamil reduces systemic vascular resistance and blood pressure the related drug nifedipine is preferable as an antihypertensive agent because it does not affect AV conduction. The effects of verapamil, including its influence on sparing myocardial ATP, make it another contender in attempts to prevent extension of the size of myocardial infarction, but there is no evidence that reduction of infarction size can be achieved in man by administering verapamil and this use remains experimental.