What is the mechanism of action of Amiodarone?

RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Pharmacology

Easy

Appeared in: RRB Nsg. Superintendent -29 April-2025 (shift-2nd)

Explanation

Amiodarone is classified as a Class III antiarrhythmic agent according to the Vaughan Williams classification.
Its primary mechanism of action is blocking the delayed rectifier potassium (K+) channels in the heart.
This blockade prolongs the repolarization phase (Phase 3) of the cardiac action potential.
Prolonging the action potential duration also increases the effective refractory period (ERP), making the cardiac tissue less susceptible to re-entrant arrhythmias.
This effect is reflected on the ECG as a prolongation of the QT interval.

Option A: This is a secondary, not primary, mechanism of Amiodarone. It does have weak calcium channel blocking (Class IV) effects, but this is not its main action.
Option B: This is a secondary, not primary, mechanism. Amiodarone has Class I effects by blocking inactivated sodium channels, but its primary classification is not as a sodium channel blocker.
Option C: This is a secondary, not primary, mechanism. Amiodarone has non-competitive beta-blocking (Class II) properties, but it is not its main classification.

Visual 1: Diagram: The cardiac action potential, illustrating the five phases and showing how Class III drugs like Amiodarone prolong Phase 3 (repolarization).
Visual 2: Chart: The Vaughan Williams classification system, listing the four main classes, their mechanisms of action, and example drugs for each class.
Visual 3: Infographic: A summary of Amiodarone's 'multi-class' actions, showing its primary Class III effect and its secondary Class I, II, and IV effects.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Mechanism of action of Amiodarone and Vaughan Williams classification of antiarrhythmic drugs as background academic context rather than a clinical decision trigger.
Amiodarone is a highly effective, broad-spectrum antiarrhythmic used for serious ventricular arrhythmias (like VT) and supraventricular arrhythmias (like atrial fibrillation), especially in patients with structural heart disease.
Due to its multiple mechanisms and long half-life, nurses must monitor patients for a wide range of adverse effects, including pulmonary toxicity (fibrosis), thyroid dysfunction (hyper- or hypothyroidism), liver toxicity, and corneal microdeposits.
Nursing interventions include obtaining baseline and periodic thyroid function tests (TFTs), liver function tests (LFTs), and pulmonary function tests (PFTs), as well as instructing patients to report symptoms like shortness of breath, persistent cough, or visual changes.

How to Approach the Question

First, identify the drug in the question stem: 'Amiodarone'.
Recall the pharmacological classification of this drug. Amiodarone is a well-known antiarrhythmic.
Access your knowledge of the Vaughan Williams classification system for antiarrhythmic drugs.
Identify Amiodarone's primary class. While it has effects from all four classes, it is predominantly a Class III agent.
Match this primary classification with the given options. 'Class III antiarrhythmic drug' is a direct match.
Eliminate the other options by recognizing them as secondary effects of Amiodarone or primary mechanisms of other drug classes.

Concept Tested & Keywords

Concept Tested: Mechanism of action of Amiodarone and Vaughan Williams classification of antiarrhythmic drugs.
Stem keywords: Amiodarone, mechanism of action
Lead-in keywords: What is
Negative lead-in flag: false

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