Verapamil

• Hypertension
• Angina
• Supraventricular Tachycardia
• Atrial Fibrillation Rate Control

Verapamil is a non-dihydropyridine calcium channel blocker used to treat hypertension, angina, and supraventricular arrhythmias. It has significant effects on both cardiac and vascular smooth muscle.

Mechanism of Action

Verapamil blocks L-type calcium channels:

• Cardiac effects: Reduces heart rate (negative chronotropy), slows AV conduction (negative dromotropy), and decreases contractility (negative inotropy)
• Vascular effects: Relaxes vascular smooth muscle, causing vasodilation
• Coronary vasodilation: Increases coronary blood flow and oxygen delivery
• Decreased cardiac workload: Reduces afterload and myocardial oxygen demand
• AV nodal blockade: Slows conduction, useful for rate control in atrial fibrillation

Available Formulations

• Immediate-release tablets: 40 mg, 80 mg, 120 mg
• Extended-release tablets/capsules: 100 mg, 120 mg, 180 mg, 200 mg, 240 mg, 300 mg, 360 mg
• Injectable: 2.5 mg/mL

Medical Uses

FDA-Approved Indications:

• Hypertension
• Angina (chronic stable, vasospastic/Prinzmetal's, unstable)
• Supraventricular tachyarrhythmias (PSVT, atrial fibrillation/flutter rate control)
• Hypertrophic cardiomyopathy (symptom relief)

Dosing Guidelines

Hypertension (Extended-Release):

• Initial: 180-240 mg once daily (or 120 mg at bedtime)
• Maximum: 480 mg daily

Angina (Immediate-Release):

• Initial: 80-120 mg three times daily
• Maximum: 480 mg daily

Atrial Fibrillation/Flutter Rate Control:

• IV: 5-10 mg (0.075-0.15 mg/kg) over 2 minutes; may repeat 10 mg after 30 minutes
• Oral: 240-480 mg daily in divided doses

PSVT (IV):

• 5-10 mg IV over 2 minutes; may repeat 10 mg after 15-30 minutes

Important Safety Information

Contraindications:

• Severe left ventricular dysfunction
• Hypotension (SBP <90 mmHg)
• Cardiogenic shock
• Sick sinus syndrome (without pacemaker)
• Second or third degree AV block (without pacemaker)
• Atrial fibrillation/flutter with accessory pathway (WPW syndrome)
• Concurrent IV beta-blocker administration

Warnings and Precautions:

• Heart failure: May worsen; use with caution if LVEF reduced
• Hepatic impairment: Reduced clearance; lower doses needed
• Renal impairment: May require dose adjustment
• Conduction abnormalities: May worsen AV block
• Hypertrophic cardiomyopathy with outflow obstruction: Use with caution

Drug Interactions

• Beta-blockers: Additive negative inotropic and chronotropic effects; avoid IV combination
• Digoxin: Verapamil increases digoxin levels 50-75%; monitor levels
• CYP3A4 substrates (simvastatin, atorvastatin): Verapamil increases statin levels; use lower statin doses
• Lithium: May reduce lithium levels; neurotoxicity possible
• Carbamazepine, phenytoin, cyclosporine, tacrolimus: Verapamil increases their levels
• Rifampin: Dramatically reduces verapamil levels

Special Populations

• Hepatic Impairment: Reduce dose; use 30% of normal dose in cirrhosis
• Renal Impairment: Monitor closely; may need reduced dose
• Elderly: Start with lower doses; increased sensitivity
• Pregnancy: Category C; use only if benefit outweighs risk
• Lactation: Present in milk; generally compatible with breastfeeding
• Pediatric: Safety and efficacy established for SVT; dose by weight