propafenone
Summary
Propafenone is a Class IC antiarrhythmic agent used to treat supraventricular and ventricular arrhythmias, particularly atrial fibrillation in patients without structural heart disease. It works by blocking fast sodium channels, significantly slowing conduction velocity without affecting action potential duration. It also has weak beta-blocking activity.
Detail
Propafenone is a Vaughan-Williams Class IC antiarrhythmic that blocks fast voltage-gated Na+ channels in cardiac tissue, causing marked slowing of conduction velocity (phase 0 of the action potential) with minimal effect on action potential duration or refractory period. It has the slowest dissociation kinetics of the Class I agents, making it the most potent sodium channel blocker in this class. Propafenone also possesses mild intrinsic beta-adrenergic blocking activity, contributing to its antiarrhythmic effects.
Clinical uses: Primarily used for pharmacologic cardioversion and maintenance of sinus rhythm in paroxysmal atrial fibrillation (the 'pill-in-the-pocket' approach for select patients), as well as for AV nodal reentrant tachycardia and other supraventricular tachycardias. It is contraindicated in patients with structural heart disease, prior MI, or reduced ejection fraction due to increased mortality risk demonstrated in the CAST trial (studied with related Class IC drugs flecainide/encainide), reflecting its proarrhythmic potential in ischemic or structurally abnormal hearts.
Pharmacokinetics: Metabolized by CYP2D6, so genetic polymorphisms can affect drug levels; poor metabolizers accumulate higher parent drug concentrations.
Adverse effects: Can cause bradycardia, AV block, and proarrhythmia (widening QRS, torsades less common than Class III agents). Bronchospasm can occur due to beta-blocking activity, making it relatively contraindicated in asthma/COPD patients. Metallic taste and dizziness are also reported.
Mnemonic: Class IC drugs 'Flecainide, Propafenone' - remember 'Can I have Please' for IC drugs. IC drugs have the most pronounced sodium channel blockade with no effect on QT/APD, contrasted with IA (moderate) and IB (mild) sodium blockade.
Sources
- Katzung's Basic and Clinical Pharmacology
- Goodman & Gilman's Pharmacological Basis of Therapeutics
- First Aid for the USMLE Step 1
- Braunwald's Heart Disease
Reviewed by AnkiBoss editorial — medical student review. Information here is for study reference only and is not medical advice. Spotted an error? Let us know.