The class III antiarrhythmic action of sotalol differs from other class III agents like amiodarone because sotalol:

• A Primarily blocks L-type calcium channels with minimal potassium channel effects
• B Combines IKr (rapid delayed rectifier K+ channel) blockade with significant β-adrenoceptor blocking activity ✓
• C Blocks both INa and IKr channels, classifying it as a class Ia/III hybrid
• D Has no risk of torsades de pointes due to its combined channel blocking properties

Explanation

Sotalol has dual class II (β-adrenoceptor blockade) and class III (IKr blockade with QT prolongation) properties. The β-blocking action slows the heart rate, while IKr blockade prolongs action potential duration and refractory period. Paradoxically, the slower heart rate from β-blockade increases the risk of bradycardia-dependent QT prolongation and torsades de pointes. Amiodarone blocks multiple channels (INa, IKr, ICa-L, Ito) plus adrenoceptors. Sotalol does not significantly block Na+ channels and is not a class Ia/III hybrid.

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

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Written and medically reviewed by the StethoPrep medical team.