Amiodarone belongs to Class III antiarrhythmics and prolongs the cardiac action potential. However, at therapeutic concentrations it also blocks which other ion channels, contributing to its broad antiarrhythmic spectrum?

• A Sodium channels (Class I) and L-type calcium channels (Class IV) only
• B Potassium channels and dopamine receptors
• C Sodium channels and alpha-1 adrenoceptors exclusively
• D Potassium channels (IKr, IKs), sodium channels (INa), calcium channels (ICaL), and has beta-adrenoceptor blocking properties (Class II) ✓

Explanation

Amiodarone is sometimes called a 'pan-class' antiarrhythmic because it has properties spanning all four Vaughan Williams classes: it blocks IKr and IKs (Class III, predominant effect—QT prolongation), INa (Class I, slows phase 0), ICaL (Class IV, AV nodal slowing), and has non-competitive beta-adrenoceptor antagonism (Class II, reduces sympathetically driven arrhythmias). This multi-channel blockade underlies its efficacy against both supraventricular and ventricular arrhythmias. It does not block dopamine receptors.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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