Verapamil Intoxication
Verapamil is a phenylalkylamine calcium-channel antagonist used mainly in cardiovascular disorders, such as hypertension, coronary artery disease, and supraventricular arrhythmias. In addition, by virtue of its vasodilatory effects on cerebral arteries and possibly its modulation of central neurotransmitters, verapamil is used for the prophylaxis of migraine and cluster headaches.

Because the formulation of verapamil may play a role in the drug's complex pharmacokinetics, one formulation of verapamil cannot be safely substituted for another. This report describes a case in which inappropriate substitution of one verapamil formulation for another had harmful consequences and briefly reviews verapamil's pharmacokinetics and pharmacodynamics.