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

• Nickson C. Verapamil Overdose
• Nickson C. Narrow Complex Tachycardia