NAPLEX Question of the Week: Ranking Antiarrhythmics

Hi everyone! This week we will test your ability to rank antiarrythmics by their mechanism of action and thus class!

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Rank the following in order from class I antiarrhythmic to class IV antiarrhythmic.

A. Dofetilide

B. Diltiazem

C. Metoprolol

D. Procainamide

Answer with rationale:

The correct order is D-C-A-B.

The term "Antiarrhythmics" strikes fear into many pharmacy students. But an organized approach to learning them. In general there are 4 broad classes of antiarrhytmics based on mechanism of action: Classes I, II, III, and IV. Class I agents block sodium channels and are further divided up into Class Ia (intermediate association/dissociation), Ib (fast association/dissociation), and Ic (slow dissociation/association). Examples within these classes include procainamide (1a), lidocaine (1b), and flecainide (1c). Class II agents, such as metoprolol,  possess beta-blocking activity. Class III agents, such as dofetilide, block potassium channels. Dofetilide due to its significant QT prolonging potential is always initiated in the inpatient setting where EKG monitoring can take place. One of the more commonly used antiarrhythmics, amiodarone, is also a Class III antiarrhythmic. Finally Class IV agents, such as diltiazem, block calcium channels.

For more reading on this topic, see our chapter in the 3rd Edition Naplex Review Guide on AccessPharmacy:§ionid=201032487

Additionally, Dr. Scott Sutton has recorded selected videos on difficult topics for students, one of which is on Antiarrhythmics:

Christopher M. Bland

Clinical Associate Professor, University of Georgia College of Pharmacy