Which drug is classified as a Class III antiarrhythmic?

Bretylium is classified as a Class III antiarrhythmic drug due to its mechanism of action that primarily involves prolonging the action potential duration and refractory period in cardiac tissues. Class III antiarrhythmics are known for blocking potassium channels, which helps to prevent or treat certain types of arrhythmias by stabilizing the heart's rhythm.

In the case of bretylium, it is particularly effective in the management of ventricular fibrillation and tachycardia. By hindering the repolarization of cardiac cells, it allows for a more organized and effective cardiac conduction, which is crucial in treating arrhythmias.

The other drugs listed belong to different classes: diltiazem is a calcium channel blocker (Class IV), quinidine is a Class I antiarrhythmic (sodium channel blocker), and lidocaine is also a Class I antiarrhythmic but specifically a Class Ib drug that primarily affects ischemic heart tissues. Understanding these classifications helps in determining the appropriate therapeutic use of each drug in managing cardiac arrhythmias.