Overview
Verapamil is a calcium channel blocker used primarily for hypertension management. It works by inhibiting calcium influx into vascular smooth muscle and cardiac cells, leading to vasodilation and reduced myocardial contractility. This drug helps lower blood pressure and reduce cardiovascular risks including stroke and myocardial infarction.
Mechanism of Action
Verapamil inhibits transmembrane calcium influx through L-type calcium channels in vascular smooth muscle and cardiac cells. This causes coronary and peripheral vasodilation, reduces myocardial contractility, slows atrioventricular conduction, and decreases heart rate.
Indications
- Treatment of hypertension
- Angina pectoris (not explicitly stated but standard indication)
- Supraventricular arrhythmias (not explicitly stated but standard indication)
Common Doses
- 120 mg
- 180 mg
- 240 mg
- 360 mg
- 480 mg
Dosage
Dosage varies based on indication and formulation. For hypertension with extended-release tablets, typical starting dose is 180-240 mg once daily, with titration up to 480 mg daily if needed. Immediate-release formulations are typically dosed 2-3 times daily.
Contraindications
- Severe left ventricular dysfunction
- Hypotension (systolic pressure <90 mmHg) or cardiogenic shock
- Sick sinus syndrome (without functioning pacemaker)
- Second- or third-degree AV block (without functioning pacemaker)
- Atrial flutter/fibrillation with accessory bypass tract (WPW, LGL syndromes)
- Known hypersensitivity to verapamil
Side Effects
- Constipation (7.3%)
- Dizziness (3.3%)
- Bradycardia
- Dyspnea (1.4%)
- Headache
- Edema
- Nausea
- Fatigue
- Hypotension
- Elevated liver enzymes
- AV conduction abnormalities
- Heart failure exacerbation
Interactions
- Beta-blockers (additive bradycardia, AV block)
- Digoxin/digitoxin (increased levels, risk of toxicity)
- CYP3A4 inhibitors (erythromycin, ritonavir - increased verapamil levels)
- CYP3A4 inducers (rifampin - decreased verapamil levels)
- Statins (simvastatin, lovastatin - increased risk of myopathy)
- Ivabradine (increased exposure, exacerbates bradycardia)
- Alcohol (inhibits elimination, prolongs intoxication)
- Lithium (neurotoxicity, variable level changes)
Counseling Points
- Take exactly as prescribed, do not crush or chew extended-release tablets
- Report dizziness, lightheadedness, or fainting
- Monitor blood pressure regularly
- Report constipation, which is common
- Avoid grapefruit juice (may increase drug levels)
- Inform all providers about verapamil use before procedures
- Do not stop abruptly without medical supervision