amiodarone

Amiodarone is the Swiss-army-knife antiarrhythmic — a single drug that calms a wide range of dangerous rhythms, from atrial fibrillation to life-threatening ventricular tachycardia. Its broad reach comes from blocking several different ion channels at once rather than just one.

Although it is filed under the potassium-channel-blocking class, it also dampens sodium and calcium currents and blocks beta receptors, which together prolong the heart cells' recovery time and steady the rhythm. It can be given by vein in emergencies or as long-term tablets.

Its great strength is that it works in hearts too weak for many other antiarrhythmics and rarely triggers the dangerous rhythm-disturbing effect that limits its peers. For that reason it is a mainstay in cardiac arrest from shockable rhythms and in difficult atrial and ventricular arrhythmias.

The catch is its long list of slow-building toxicities. Because it lingers in the body for weeks to months and contains iodine, it can affect the thyroid, lungs, liver, skin, and eyes, so people on long-term therapy have periodic thyroid, liver, and lung checks.