Vaughan Williams Classification of Antiarrhythmic Drugs

The Vaughan Williams classification scheme is relatively simple and is useful as a conversational shorthand based on mechanism of action, for its ability to predict adverse effects, and for preliminary decisions regarding drug therapy , but it has a number of important drawbacks:

• Drugs within a class are not necessarily clinically similar; a patient may respond well to one drug in a given class, but not another

• Almost all of the currently available drugs have multiple actions ; it is rarely apparent which of these actions is responsible for suppression of an arrhythmia in a given patient

• The metabolites of many of the drugs contribute to or are primarily responsible for their antiarrhythmic actions (e.g.- procainamide and its metabolite, N-acetylprocainamide; encainide and its metabolite, 3-methoxy-O-desmethylencainide)

  • The stereoisomers of several drugs can have different actions :

    • The stereo isomers of disopyramide (Class IA) have opposite effects on repolarization; the predominant effect in a given patient depends on the degree of stereospecificity exhibited in elimination of the drug by that patient

    • Only the l-isomer of sotalol has beta-adrenergic blocking activity

Note that some of the most useful and widely used drugs (quinidine, procainamide, disopyramide, amiodarone, sotalol) have multiple actions which might explain their utility in treating a broad range of arrhythmias or arrhythmias of unknown cause.

Category: Pharmacology Notes