💊 Amiodarone

Amiodarone is a Class III antiarrhythmic agent, according to the Vaughan Williams classification, primarily acting by blocking potassium channels. It also possesses properties of Class I, II, and IV antiarrhythmics.

Amiodarone prolongs the cardiac action potential and refractory period in all cardiac tissues by blocking potassium channels (Class III effect). It also blocks sodium channels (Class I), beta-adrenergic receptors (Class II), and calcium channels (Class IV), contributing to its broad antiarrhythmic efficacy. This multifaceted action slows sinus rate, prolongs PR and QT intervals, and decreases AV nodal conduction.

Amiodarone is used for a wide range of supraventricular and ventricular arrhythmias, particularly when other antiarrhythmics are ineffective or contraindicated. Key indications include atrial fibrillation (rate and rhythm control), atrial flutter, and life-threatening ventricular arrhythmias such as ventricular tachycardia and ventricular fibrillation (especially in cardiac arrest). It is also used for arrhythmias in patients with structural heart disease.

Absolute contraindications include sinus bradycardia, sinoatrial block, second- or third-degree AV block (unless a pacemaker is in situ), and severe thyroid dysfunction. Known hypersensitivity to amiodarone or iodine is also a contraindication. Relative contraindications include severe liver disease and severe lung disease.

Amiodarone has a wide range of significant adverse effects due to its long half-life and tissue accumulation. These include thyroid dysfunction (hypo- or hyperthyroidism), pulmonary fibrosis, liver dysfunction, corneal microdeposits, photosensitivity (blue-grey skin discoloration), and peripheral neuropathy. Bradycardia and QT prolongation with Torsades de Pointes are also possible.

Due to its extensive side effect profile, comprehensive monitoring is essential. This includes baseline and regular (e.g., 6-monthly) thyroid function tests (TSH, T3, T4), liver function tests, and electrolytes. Baseline and annual chest X-rays and lung function tests (DLCO) are recommended. Regular ECGs are needed to monitor for QT prolongation and bradycardia. Ophthalmological examination for corneal deposits may also be required.

Always check for allergies, especially iodine. Significant drug interactions include warfarin (potentiates anticoagulation), digoxin (increases digoxin levels), and simvastatin (increased risk of myopathy). Counsel patients about photosensitivity (sun protection), the need for regular monitoring, and to report any new symptoms like breathlessness, cough, or jaundice immediately.

Amiodarone is a highly effective antiarrhythmic but its use is limited by its significant and potentially life-threatening side effects. It has a very long half-life (weeks to months), meaning adverse effects can persist long after discontinuation. It is a key drug in advanced life support algorithms for refractory ventricular fibrillation/pulseless VT. Careful patient selection and rigorous monitoring are crucial.

SBA questions frequently focus on the extensive and serious side effect profile of amiodarone, particularly pulmonary fibrosis, thyroid dysfunction, and liver toxicity. Questions might also test its use in cardiac arrest algorithms or its broad spectrum of antiarrhythmic activity. The long half-life and need for extensive monitoring are common themes.