Pharm 101: Antiarrhythmic Agents

Classification system

Vaughan-Williams classification (four classes)

Class I

• Act via Na channel blockade
• Subclasses reflect effects on:
  • Action potential duration (APD)
  • Kinetics of Na channel blockade

Class	Examples	Effects
IA	Procainamide, Quinidine, Disopyramide	Prolong APD, dissociate (from channel) with intermediate kinetics
IB	Lignocaine	Shorten APD in heart, dissociate with rapid kinetics
IC	Flecainide, Propafenone	Minimal effects on APD, dissociated with slow kinetics

Class II

• Sympatholytic
• Beta-adrenergic blocking activity
• Examples:
  • Propranolol
  • Esmolol

Class III

• Prolong APD
• Block rapid component of delayed rectifier K current, I_Kr
• Examples:
  • Amiodarone
  • Sotalol

Class IV

• Blockade of cardiac calcium current
• Slows conduction in regions where AP upstroke is calcium dependent, e.g. SA and AV nodes
• Examples:
  • Verapamil
  • Diltiazem

Other information

• Drugs may have multiple classes of action e.g. amiodarone shares all four classes of action
• Certain agents do not fit this classification scheme:
  • Adenosine
  • Magnesium

References

• Katzung BG. Basic and Clinical Pharmacology. 14e. 2018: 237