10.5 : 抗不整脈薬: カリウムチャネル遮断薬としてのクラス III 薬剤

Class III antiarrhythmic drugs primarily act by blocking K⁺ channels or by blocking inactivated  Na⁺ channels.

This prolongs the action potential and refractory period without impacting the resting membrane potential.

These actions decrease the sinus rate and AV conduction while increasing the threshold for fibrillation.

The widely used Class III drug, amiodarone, weakly blocks Ca²⁺ channels and adrenergic receptors.

However, the presence of iodine and its long half-life causes adverse effects like pulmonary fibrosis, optic neuritis, and thyrotoxicity.

Dronedarone lacks iodine and has a shorter half-life, reducing toxicity.

Sotalol is a racemic mixture that exhibits class III actions in addition to β-blocking activity via its ʟ-isomer.

All class III drugs generally risk proarrhythmic side effects due to prolonged action potentials and extended QT intervals.

In fact, dofetilide and ibutilide are administered only under medical supervision.