Which of the following are class IA antiarrhythmic drugs?

• A. Amiodarone and Dofetilide
• B. Lidocaine and Mexiletine
• C. Quinidine and Procainamide
• D. Sotalol and Ibutilide

Answer: (C)

Class IA antiarrhythmic drugs are sodium channel blockers with intermediate on-off kinetics and they prolong the cardiac action potential duration. This combination slows conduction and extends repolarization, which lengthens the QT interval and helps suppress reentrant or ectopic rhythms. Quinidine and Procainamide fit this profile because they block fast sodium channels with intermediate kinetics and extend the action potential duration, defining the class IA effect. The other drugs belong to different classes: lidocaine and mexiletine are class IB (sodium channel blockers with minimal AP prolongation), while sotalol and ibutilide are class III (potassium channel blockers that mainly prolong repolarization). Amiodarone and dofetilide are also class III agents (amiodarone has multi-class actions but is categorized primarily as class III).