Which drugs are Class Ia antiarrhythmic drugs?

• A. Quinidine, Procainamide, Disopyramide (Norpace)
• B. Amiodarone, Sotalol, Diltiazem
• C. Lidocaine, Mexiletine, Phenytoin
• D. Flecainide, Propafenone, Moricizine

Answer: (A)

Class Ia antiarrhythmics are moderate sodium channel blockers that also prolong the action potential by affecting repolarization. They slow conduction and lengthen the duration of the cardiac action potential, which shows up as QRS widening and QT prolongation on the ECG. Quinidine, Procainamide, and Disopyramide exemplify this group, so they’re the correct set to identify as Class Ia. These drugs are used for a variety of arrhythmias but carry notable side effects and proarrhythmic risk, reflecting their significant effects on both depolarization and repolarization.

The other listed drugs belong to different classes: Amiodarone and Sotalol are primarily potassium-channel blockers (Class III) with broad effects; Diltiazem is a calcium-channel blocker (Class IV) that mainly slows AV nodal conduction. Lidocaine and Mexiletine are short-acting sodium channel blockers (Class Ib) with minimal impact on the action potential duration, used mainly for ventricular arrhythmias. Phenytoin is also a sodium channel blocker with Ib-like properties. Flecainide and Propafenone are strong sodium channel blockers (Class Ic) with little effect on overall action potential duration, and Moricizine is often grouped with Ic.