Amiodarone

Amiodarone is a class III antiarrhythmic that prolongs the action potential and refractory period by blocking potassium channels, but it also blocks sodium, calcium, and beta-adrenergic receptors — making it uniquely broad-spectrum. It treats life-threatening ventricular tachycardia (VT), ventricular fibrillation (VF), and refractory atrial fibrillation. Its half-life is extraordinarily long — 40 to 55 days — meaning drug effects and toxicities persist weeks after discontinuation. IV loading doses are given through a central line when possible because peripheral infusion causes severe phlebitis; an inline filter is required. Oral maintenance follows. Baseline and ongoing monitoring includes pulmonary function tests (pulmonary fibrosis is potentially fatal), thyroid function (TSH — the drug contains iodine and can cause hypo- or hyperthyroidism), liver function tests (hepatotoxicity), and annual ophthalmologic exams (corneal microdeposits, optic neuropathy). The QT interval must be monitored continuously during IV infusion because excessive prolongation leads to torsades de pointes. Photosensitivity and blue-gray skin discoloration develop with long-term use; patients need sunscreen and protective clothing. Amiodarone dramatically increases digoxin and warfarin levels — doses of both must be reduced, often by half.