Which medication is NOT a Class Ia antiarrhythmic drug?

Which medication is NOT a Class Ia antiarrhythmic drug?

• A. Quinidine
• B. Procainamide
• C. Disopyramide
• D. Amiodarone

Answer: (D)

Class Ia antiarrhythmics are moderate sodium channel blockers that slow conduction (through phase 0) and prolong the action potential duration, which lengthens the QT interval. The drugs Quinidine, Procainamide, and Disopyramide all fit this pattern, sharing the characteristic Na+ blockade with intermediate kinetics and a net AP prolongation. Amiodarone, by contrast, is primarily classified as a Class III antiarrhythmic because its dominant effect is potassium channel blockade that prolongs repolarization. It also has a mix of effects on other channels and receptors, but its main categorization is Class III, not Class Ia. Therefore, amiodarone is not a Class Ia antiarrhythmic.

Class Ia antiarrhythmics are moderate sodium channel blockers that slow conduction (through phase 0) and prolong the action potential duration, which lengthens the QT interval. The drugs Quinidine, Procainamide, and Disopyramide all fit this pattern, sharing the characteristic Na+ blockade with intermediate kinetics and a net AP prolongation.

Amiodarone, by contrast, is primarily classified as a Class III antiarrhythmic because its dominant effect is potassium channel blockade that prolongs repolarization. It also has a mix of effects on other channels and receptors, but its main categorization is Class III, not Class Ia. Therefore, amiodarone is not a Class Ia antiarrhythmic.