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
ClassExamplesEffects
IAProcainamide, Quinidine, DisopyramideProlong APD, dissociate (from channel) with intermediate kinetics
IBLignocaineShorten APD in heart, dissociate with rapid kinetics
ICFlecainide, PropafenoneMinimal effects on APD, dissociated with slow kinetics

Class II
  • Sympatholytic
  • Beta-adrenergic blocking activity
  • Examples:

Class III
  • Prolong APD
  • Block rapid component of delayed rectifier K current, IKr
  • Examples:

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

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:

References

Pharm 101 700

Pharmacology 101

Top 200 drugs

MBBS (UWA) CCPU Emergency Medicine Trainee with interests in medical education, ECG interpretation, and the use of point-of-care ultrasound in the undifferentiated patient. Co-author of the LITFL ECG Library | Twitter

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