Pharm 101: Verapamil

Class

Calcium channel blocker
Class IV antiarrhythmic


Pharmacodynamics
  • Blocks both activated and inactivated L-type calcium channels (alpha-1 subunit)
  • Reduces frequency of opening when depolarised resulting in decreased transmembrane calcium current and calcium influx
  • Cardiac effects:
    • Prolongs AV nodal conduction time and ERP
    • Negative inotrope
    • Reduced myocardial oxygen demand
    • Vascular smooth muscle relaxation (less than dihydropyridines) –> reduced coronary artery spasm
  • Extracardiac effects:
    • Peripheral vasodilation
    • Arterioles are more sensitive than veins, therefore orthostatic hypotension uncommon

Pharmacokinetics
  • PO or IV administration
  • Bioavailability 22% due to high first pass effect
  • High plasma protein binding
  • Extensive metabolism
  • Half-life 6 hours

Clinical uses
  • Angina
  • Hypertension
  • Supraventricular arrhythmias
  • Migraine

Adverse effects
  • Extension of therapeutic effect, exacerbated by beta-blockers
  • Cardiac:
    • Bradycardia
    • AV block
    • VF/hypotension if used in treatment of VT
    • Cardiotoxic effects are dose-related
  • Non-cardiac:
    • Flushing
    • Dizziness
    • Nausea
    • Constipation
    • Peripheral edema

Further Reading

Pharm 101 700

Pharmacology 101

Top 200 drugs

MBBS (UWA) CCPU (RCE, Biliary, DVT, E-FAST, AAA) Emergency Medicine Advanced Trainee in Melbourne, Australia. Special interests in diagnostic and procedural ultrasound, medical education, and ECG interpretation. Editor-in-chief of the LITFL ECG Library. Twitter: @rob_buttner

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