Amiodarone prolongs the QT interval primarily by blocking which ion channel?

• A L-type calcium channels, prolonging the plateau phase
• B Inward rectifier K+ channels (IK1), prolonging phase 4
• C hERG potassium channels (IKr), delaying ventricular repolarisation ✓
• D Fast sodium channels, prolonging phase 0

Explanation

Amiodarone's predominant class III antiarrhythmic effect is blockade of the hERG-encoded IKr (rapidly activating delayed rectifier K+ channel), which prolongs phase 3 repolarisation and extends the action potential duration, manifesting clinically as QT prolongation. While amiodarone also blocks sodium channels, calcium channels, and beta-receptors (multi-channel effects), IKr blockade is the principal mechanism for QT prolongation.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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