Verapamil

Introduction Overview

Generic Name

verapamil

Brand Name

Calan, Calan SR, Isoptin SR, Verelan, Verelan PM, Isoptin, Isoptin I.V., Covera-HS

Dosage Form

intravenous solution (2.5 mg/mL), oral capsule extended release (100 mg to 360 mg per 24 hours), oral tablet immediate release (40 mg, 80 mg, 120 mg), oral tablet extended release (120 mg, 180 mg, 240 mg per 12 hours)

Drug Class

Calcium channel blockers; Group IV antiarrhythmics

Pharmacokinetics

Absorption: Verapamil is well absorbed from the gastrointestinal tract when administered orally, with bioavailability affected by significant first-pass hepatic metabolism. Peak plasma concentrations are generally reached within 1 to 2 hours following immediate-release formulations and later with extended-release forms. Factors such as food intake can influence absorption rate but not overall extent. IV administration bypasses absorption variability, providing immediate systemic availability.

Distribution: Verapamil is extensively distributed throughout the body tissues, with a volume of distribution approximately 3 to 5 L/kg. It binds highly to plasma proteins (~90%) and crosses the blood-brain barrier moderately. The drug distributes into cardiac, vascular smooth muscle, liver, and kidney tissues, reflecting its therapeutic targets.

Metabolism: Verapamil undergoes extensive hepatic metabolism primarily by cytochrome P450 3A4 enzymes. It is subject to significant first-pass metabolism leading to formation of multiple metabolites, some of which retain pharmacologic activity. Genetic polymorphisms and enzyme inhibitors can markedly alter metabolic rate and plasma concentrations.

Elimination: Verapamil and its metabolites are eliminated primarily via biliary excretion into feces and to a lesser extent via renal excretion. The plasma elimination half-life varies with formulation, averaging 3 to 7 hours for immediate release and prolonged half-life for extended-release products. Hepatic or renal impairment can significantly alter drug clearance necessitating dose adjustments.

Dosage Forms

Available Dosage Forms:
- Intravenous solution: 2.5 mg/mL concentration for rapid administration under ECG monitoring.
- Oral immediate-release tablets: 40 mg, 80 mg, and 120 mg.
- Oral extended-release tablets: 120 mg, 180 mg, 240 mg, administered typically twice daily.
- Oral extended-release capsules: 100 mg, 120 mg, 180 mg, 200 mg, 240 mg, 300 mg, and 360 mg per 24 hours, providing once-daily dosing options.

Dosages for Adults and Adolescents:
- Hypertension and Angina: Typical oral doses range from 240 mg to 480 mg daily in divided doses or as extended-release once daily; initial dosing often starts at 180 mg/day.
- Arrhythmia: Immediate-release tablets are used at doses ranging from 240 mg to 360 mg daily in divided doses. Intravenous dosing is individualized for acute control.
- For intravenous administration, doses range from 0.075 to 0.15 mg/kg IV over 2 minutes, with repeat dosing as needed under continuous cardiac monitoring.

Specific Patient Populations:
- In hepatic impairment, dosage reductions and careful monitoring are advised due to decreased metabolism.
- In renal impairment, although elimination is predominantly hepatic, monitoring is recommended.
- Use in pediatrics is limited but intravenous use is approved under strict monitoring for acute arrhythmias.
- Extended-release formulations should not be crushed or chewed; certain capsules may be opened and contents mixed with applesauce if swallowing is difficult, under pharmacist guidance.
- Dose adjustments may be required when switching between brands or formulations due to pharmacokinetic differences.

Mechanism Of Action

Verapamil acts as a calcium channel blocker by inhibiting the influx of extracellular calcium ions through voltage-dependent L-type calcium channels in cardiac and vascular smooth muscle cells. This blockade reduces intracellular calcium concentrations, which leads to decreased myocardial contractility (negative inotropic effect), slowed conduction through the atrioventricular (AV) node (negative dromotropic effect), and decreased heart rate (negative chronotropic effect).

At the cellular level, verapamil stabilizes cardiac electrical activity by suppressing aberrant pacemaker activity and slowing conduction velocity within the sinoatrial (SA) and AV nodes, thereby controlling supraventricular tachyarrhythmias. It decreases myocardial oxygen demand by reducing myocardial contractility and heart rate and dilates coronary arteries to improve oxygen delivery.

Biochemically, verapamil binds to specific sites on the alpha-1 subunit of L-type calcium channels, altering channel conformation and reducing calcium channel opening probability during depolarization. This action is selective for cardiac and vascular smooth muscle calcium channels and does not affect skeletal muscle calcium channels significantly.

Clinically, these effects translate to effective treatment of hypertension by vasodilation and reduction of peripheral vascular resistance, relief of angina by balancing oxygen supply and demand, and normalization of certain arrhythmias by suppressing abnormal cardiac electrical conduction. Compared to other calcium channel blockers, verapamil has a pronounced cardiac depressant effect and is distinct from dihydropyridines in its antiarrhythmic properties. Multiple clinical trials support these mechanisms, demonstrating verapamil’s efficacy in controlling hypertension, angina pectoris, and supraventricular tachyarrhythmias.

Pharmacological Actions

Blocks L-type calcium channels in cardiac and vascular smooth muscle.
Negative inotropic effect reducing myocardial contractility.
Negative chronotropic effect slowing heart rate via SA node suppression.
Negative dromotropic effect slowing AV nodal conduction.
Coronary and peripheral arterial vasodilation reducing systemic vascular resistance.
Suppresses supraventricular tachyarrhythmias by stabilizing cardiac conduction.
Decreases myocardial oxygen demand and increases oxygen supply.
Modulates autonomic nervous system effects on heart by calcium channel blockade.
Alters intracellular calcium dynamics impacting cellular excitation-contraction coupling.
Exhibits antiarrhythmic activity characteristic of Group IV antiarrhythmics.

Therapeutic Or Clinical Uses

Treatment of hypertension to lower elevated blood pressure.
Management of angina pectoris (chest pain) to improve cardiac oxygen delivery.
Control of supraventricular tachyarrhythmias including atrial fibrillation and atrial flutter.
Acute management of certain arrhythmias via intravenous administration.
Prevention of recurrent angina attacks in chronic stable angina patients.
Symptomatic treatment of Prinzmetal’s (variant) angina by coronary vasodilation.
Reduction of ventricular rate in atrial fibrillation and atrial flutter.
Management of hypertrophic cardiomyopathy symptoms via reduced myocardial contractility.
Off-label use in certain neuromuscular disorders due to calcium channel modulation.
Alternative option for patients intolerant to beta blockers for arrhythmia control.

Side Or Adverse Effects

Constipation, commonly due to decreased gastrointestinal motility.
Dizziness and headache resulting from vasodilation and blood pressure reduction.
Hypotension with potential light-headedness or syncope.
Peripheral edema caused by arteriolar dilation and fluid retention.
Bradycardia and atrioventricular block due to cardiac conduction slowing.
Exacerbation of heart failure due to negative inotropic effects in susceptible patients.
Nausea and gastrointestinal discomfort.
Flu-like symptoms including infections and fatigue.
Rash and hypersensitivity reactions including rare anaphylaxis.
Liver enzyme elevations indicating potential hepatotoxicity.
Rare pulmonary edema and signs of fluid overload.
Worsening of pre-existing conduction abnormalities such as sick sinus syndrome.
Possible elevation in blood sugar levels in some patients.
Dizziness or weakness upon standing (orthostatic hypotension).
Rare neurological effects like confusion or hallucinations in overdose scenarios.

Precautions

Use caution in patients with congestive heart failure as verapamil may exacerbate symptoms.
Monitor liver function tests regularly due to potential hepatotoxicity.
Assess heart rate and rhythm frequently to detect bradyarrhythmias or AV block.
Avoid abrupt discontinuation to prevent rebound hypertension or arrhythmias.
Use caution when combined with beta-blockers due to additive cardiac depressant effects.
Adjust dose in renal or hepatic impairment to minimize toxicity.
Be alert for signs of hypotension especially during initiation and dose escalation.
Avoid use in patients with sick sinus syndrome or AV block unless a pacemaker is present.
Advise patients to rise slowly from sitting or lying positions to reduce dizziness risk.
Screen for drug interactions including CYP3A4 inhibitors and inducers prior to therapy.
Educate patients on signs of allergic reactions and when to seek emergency care.
Advise avoiding grapefruit products to prevent elevated verapamil levels.
Monitor blood pressure routinely to ensure therapeutic effectiveness and safety.
Consider pregnancy status and avoid use unless benefits outweigh risks.
Caution against operating machinery if impaired by dizziness or hypotension.

Warnings

Contraindicated in patients with severe left ventricular dysfunction or heart failure with reduced ejection fraction.
Do not use in patients with sick sinus syndrome or second- or third-degree AV block unless a pacemaker is present.
Risk of severe bradycardia, hypotension, or heart block especially with intravenous administration.
Avoid use in Wolff-Parkinson-White, Lown-Ganong-Levine syndrome combined with atrial fibrillation due to risk of rapid ventricular rates.
Concurrent use with intravenous beta-blockers may cause profound hypotension and heart block.
Risk of hepatic injury necessitates close monitoring of liver function during therapy.
Avoid grapefruit juice consumption as it inhibits metabolism leading to elevated verapamil plasma levels and toxicity.
Use caution in patients with myasthenia gravis or muscular dystrophy as verapamil may exacerbate muscle weakness.
Potential for fluid retention and pulmonary edema requiring monitoring in susceptible individuals.
Overdose can be fatal with symptoms such as severe hypotension, bradyarrhythmias, and cardiogenic shock.
Pregnancy safety has not been established; use only if clearly needed after risk-benefit assessment.
Avoid abrupt withdrawal to prevent rebound hypertension or arrhythmias.
Monitor for signs of allergic reactions including angioedema and anaphylaxis.
Alcohol may potentiate hypotensive and CNS depressant effects of verapamil.
Caution in elderly patients due to increased susceptibility to hypotension and bradycardia.

Contraindication

Known hypersensitivity or allergy to verapamil or any formulation components.
Severe left ventricular systolic dysfunction or heart failure.
Sick sinus syndrome or sinoatrial node disease without pacemaker.
Second- or third-degree atrioventricular block without a pacemaker.
Hypotension with systolic blood pressure less than 90 mmHg.
Wolff-Parkinson-White syndrome or Lown-Ganong-Levine syndrome in patients with atrial fibrillation or atrial flutter.
Concurrent intravenous beta-blocker administration due to risk of cardiac conduction depression.
Severe hypotension or cardiogenic shock.
Known severe hepatic impairment due to impaired metabolism.
Patients with cardiogenic shock or unstable angina.
Use in patients with certain types of brain tumors without careful evaluation.
Presence of severe bradycardia (<50 bpm) before treatment initiation.
Use contraindicated during breastfeeding due to risk of drug transmission to infant.
Use contraindicated when urgent IV beta-blocker therapy is required concurrently.
Patients with history of verapamil-induced allergic or anaphylactic reactions.

Drug Interactions

Additive negative inotropic and chronotropic effects when combined with beta-blockers (atenolol, metoprolol, propranolol).
Inhibition of metabolism by CYP3A4 inhibitors such as ketoconazole, erythromycin, and grapefruit juice leading to increased verapamil plasma levels.
Potentially reduced effectiveness of CYP3A4 inducers like rifampin, carbamazepine, and St. John's wort decreasing verapamil levels.
Increased risk of severe hypotension and bradycardia when used with other calcium channel blockers.
Interaction with digoxin causing elevated digoxin levels and increased risk of toxicity.
Additive AV nodal blocking effects with antiarrhythmics such as disopyramide and amiodarone leading to conduction disturbances.
Verapamil may increase serum levels of lithium and cyclosporine by affecting renal clearance.
Interaction with carbamazepine may decrease verapamil effectiveness.
Use with statins metabolized by CYP3A4 (simvastatin, atorvastatin) may increase statin levels and risk of myopathy.
Concomitant use with anti-hypertensive agents can enhance hypotensive effects requiring monitoring and possible dose adjustments.
May interfere with the metabolism of benzodiazepines leading to increased sedation.
Combination with rifampin or phenytoin can reduce verapamil plasma concentrations.
Herbal supplements such as St. John's wort may reduce verapamil efficacy via enzyme induction.
Increased risk of myopathy when used with colchicine due to altered drug metabolism.
Verapamil may increase serum concentrations of carbamazepine leading to toxicity.

Preparations Of The Drug

Intravenous solution for injection 2.5 mg/mL for acute arrhythmia management.
Immediate-release oral tablets in doses of 40 mg, 80 mg, and 120 mg.
Extended-release oral tablets available as 120 mg, 180 mg, and 240 mg, administered twice daily.
Extended-release oral capsules with dosing options ranging 100 mg to 360 mg per 24 hours for once-daily administration.
Various brand formulations including Calan, Calan SR, Verelan, Verelan PM, Isoptin, Isoptin I.V., and Covera-HS supporting different release profiles.
Modified-release formulations designed for steady plasma levels to improve adherence and reduce side effects.
Oral formulations available with instructions regarding whether tablets can be crushed or capsules opened for patients with swallowing difficulties.
Parenteral injectable form intended for hospital use with continuous cardiac monitoring.
Unit dose packaging for intravenous administration to support precise dosing under medical supervision.
Pharmaceutical preparations available in multiple countries with regulatory approvals for indicated uses.
Pharmacy compounded liquid forms are rare but may be used in special populations requiring individualized dosing.
Oral formulations have different excipients and release mechanisms influencing pharmacokinetics and patient preference.
Some extended-release products incorporate osmotic pump technology to maintain plasma drug levels.
All preparations should be stored at controlled room temperature away from moisture and heat to preserve stability.
Packaging includes patient information leaflets guiding appropriate use, side effect monitoring, and storage conditions.