This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Medicine
[{'content': 'Ibutilide acts by \nSelect and explain. \nA. Blockade of Na+ current, B. Interference with the action of catecholamines at the b-adrenergic receptor, C. Delay of repolarization due to inhibition of K+ current, D. Interference with calcium conductance', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ibutilide is a class III antiarrhythmic drug.The classes of antiarrhythmic action are:- Class I, Local anaesthetic effect due to blockade of Na+ currentClass I antiarrhythmics have been fuher subdivided based on the kinetics and potency of Na+ channel bindingClass Ia agents (quinidine, procainamide) are those with moderate potency and intermediate kinetics;Class Ib agents (lidocaine, mexiletine) are those with low potency and rapid kinetics; and Class Ic drugs (flecainide, propafenone) are those with high potency and the slowest kinetics.Class II: Interference with the action of catecholamines at the b-adrenergic receptor (Atenolol, Propranolol, Esmolol, Metoprolol)Class III: Delay of repolarization due to inhibition of K+ current or activation of depolarizing current (Amiodarone, Sotalol, Ibutilide, Dofetilide)Class IV: Interference with calcium conductance (Diltiazem, Verapamil)Harrison 19e pg: 273e-6', 'role': 'assistant'}]