amiodaroni

Amiodarone is a prescription antiarrhythmic medication used to treat and prevent a range of supraventricular and ventricular tachyarrhythmias. It is classified as a Vaughan Williams class III agent, but it has properties of several classes, including sodium channel blockade, beta-adrenergic antagonism, and calcium channel effects. Amiodarone is commonly used for atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation, particularly when other therapies are not suitable or have failed.

Pharmacology and pharmacokinetics: Amiodarone blocks potassium channels, prolonging the cardiac action potential and refractory period, which helps suppress reentry circuits. It also slows conduction and exhibits additional antiarrhythmic effects through sodium and calcium channel blockade and beta-adrenergic inhibition. The drug is highly lipophilic and accumulates in adipose tissue and several organs, including the liver, lungs, and skin. It has a very long elimination half-life, often weeks to months, so effects can persist after stopping therapy.

Administration and monitoring: Amiodarone is available in oral and intravenous forms. Dosing varies by indication and regimen; loading regimens are followed by maintenance dosing. Because of the drug’s long half-life and potential toxicities, patients require regular monitoring, including thyroid, liver, and pulmonary assessments, and, if needed, imaging or testing for adverse effects. Drug interactions with warfarin, digoxin, and certain other antiarrhythmics are common and may require dose adjustments.

Adverse effects and safety: Serious adverse effects include pulmonary toxicity (interstitial pneumonitis and fibrosis), liver injury, thyroid dysfunction due to its iodine content (hypothyroidism or hyperthyroidism), corneal deposits with possible visual symptoms, photosensitivity and skin discoloration, neuropathy, bradycardia, and AV block. Contraindications include severe bradycardia or high-grade AV block without a pacemaker, cardiogenic shock, and known hypersensitivity to amiodarone. Pregnancy and breastfeeding are generally avoided, and use requires careful risk–benefit assessment.