Verapamil hydrochloride, a prototype
calcium antagonist, is now marketed in the United States for the acute treatment of supraventricular
tachyarrhythmias and for chronic management of vasospastic and
chronic stable angina. It inhibits the slow inward channel in in the heart and blocks
calcium influx in smooth muscle. Its intrinsic negative inotropic action, which is apparent in isolated tissues, is offset in vivo by peripheral vasodilation. It has a mild, noncompetitive sympathetic antagonist effect; its most important electrophysiologic action is a depression of AV nodal conduction, accounting for its effect in supraventricular
tachyarrhythmias. Its hemodynamic actions are characterized by a complex interplay of changes in preload, afterload, contractility, heart rate, and coronary blood flow. It does not depress cardiac function, except in severe
heart failure. The
drug has a mild dilator action on coronary arteries and reverses
ergonovine-induced vasoconstriction. Controlled trials have established its role in
Prinzmetal's variant angina,
unstable angina, and
chronic stable angina. It has also been found to be effective in obstructive
cardiomyopathies. The potential role of
verapamil in such conditions as
hypertension, cardioprotection, and Raynaud's phenomenon needs further evaluation; at present these indications have not been approved by the Food and Drug Administration. The most common side effects include
constipation,
skin rash, and
dizziness;
AV block,
heart failure, and sinus arrest may occasionally be encountered, especially when ventricular function is compromised or conduction system disease is present.