Amiodarone is classified as which type of antiarrhythmic?

• A. Potassium channel blocker (Class III)
• B. Sodium channel blocker (Class I)
• C. Beta-blocker (Class II)
• D. Calcium channel blocker (Class IV)

Answer: (A)

Amiodarone is categorized as a potassium channel blocker because its dominant effect is to block outward potassium currents during repolarization. This slows the repolarization phase, lengthens the action potential duration, and increases the effective refractory period in cardiac tissue, which helps suppress reentrant tachyarrhythmias. That primary action places it in Class III antiarrhythmics.

It's true that amiodarone also has effects from other classes—it can weakly block sodium channels, act on beta receptors, and influence calcium channels—so it has a very broad antiarrhythmic profile. However, when classifying by the main mechanism, the potassium channel blockade defining Class III is the key. The other options describe mechanisms that are characteristic of different classes (sodium channel blockers slow conduction, beta blockers reduce AV nodal conduction, calcium channel blockers affect the AV node), which are not the primary action of amiodarone.