verapamil

Verapamil is a calcium channel blocker in the phenylalkylamine class. It inhibits L-type calcium channels in cardiac muscle and vascular smooth muscle, leading to decreased myocardial contractility, slowed AV nodal conduction, and dilation of peripheral arteries. These actions reduce heart rate, lower blood pressure, and can relieve ischemia.

Verapamil is used to treat hypertension and various forms of angina, including vasospastic (variant) angina. It is also employed to control certain supraventricular tachyarrhythmias, especially atrial fibrillation or flutter with rapid ventricular response, by slowing AV conduction. It may be prescribed off-label for migraine prophylaxis in some patients.

Pharmacokinetics and administration: verapamil is available by mouth and by intravenous injection. It is well absorbed but undergoes substantial first-pass hepatic metabolism. Metabolism is mainly via the cytochrome P450 3A4 pathway, with active and inactive metabolites. Food and formulation can affect absorption. The half-life varies by preparation (roughly 3–7 hours for immediate-release; longer for extended-release). Excretion occurs mainly in the urine and feces.

Adverse effects and safety: common adverse effects include constipation, dizziness, flushing, edema, and bradycardia. More serious risks are hypotension and conduction abnormalities. It can worsen heart failure with reduced ejection fraction and is generally avoided in severe left ventricular dysfunction. Contraindications include severe hypotension, cardiogenic shock, second- or third-degree AV block, and sick sinus syndrome without a pacemaker.

Interactions: verapamil interacts with beta-blockers and digoxin, increasing risks of bradycardia and AV block. It inhibits or is affected by CYP3A4 inhibitors (such as certain azoles and macrolide antibiotics), and grapefruit juice may raise levels. Coadministration with nitrates can potentiate hypotension.