**1. Introduction**

Antiarrhythmic drugs are used to suppress abnormal heart rhythms and have been differen‐ tiated by their antiarrhythmic action according to the classification system developed by Vaughen-Williams in 1970 [1]. The classification includes five major groups of antiarrhythmic drugs, classes I, II, III, IV and V (Table 1). Class I agents are sodium channel blockers, class II are beta blockers, class III are potassium channel blockers, class IV are calcium channel blockers and class V agents work by unknown mechanisms. The class I agents are classified into class Ia, Ib and Ic. Ia class includes Quinidine, Procainamide and Dispopyramide. They slow the rate of rise of phase 0, lengthen the refractory period and the width of the monophasic action potential. Quinidine is one of the oldest antiarrhythmic agents derived from the cinchona tree

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bark and has anti malarial, antipyretic and antiarrhythmic effects. Procainamide and its main metabolite, N-acetyl Procainamide are effective for treating supraventricular and ventricular arrhythmias. Disopyramide has three important side effects. It is vagolytic causing urinary retention, constipation and dry mouth. The class 1b agents are pure sodium channel blockers. This class includes Lidocaine, Phenytoin Mexiletine and Tocainide. Class Ib antiarrhythmic agents used only for the management of ventricular tachyarrhythmia. The class Ic agents are strong sodium channel blockers. This class comprises of Flecainide, Encainide, Propafenone and Moricizine. They are being used to treat ventricular and supraventricular tachyarrhyth‐ mia. They are contraindicated in patients with structural heart disease due to the risk of precipitating life-threatening ventricular arrhythmias. Class II drugs include Metoprolol, Carvedilol, Atenolol, Propranolol and Bisoprolol. They antagonize beta-receptors inhibiting the effect of the sympathetic nervous system resulting in decreased heart rate, contractility and conductivity. The class III agents are drugs that block the potassium channel as their main anti arrhythmic effect. This class includes Sotalol, Dofetilide, Ibutilide, and Amiodarone. They exert their effect by prolonging the refractory period. Sotalol is a nonspecific beta adrenergic receptor blocker with potassium channel blocking properties that is used in managing ventricular arrhythmias and atrial fibrillation. Dofetilide is a potassium channel blocker and excreted by the kidneys. Ibutilide is a short-acting intravenous potassium channel blocker that is used only for the acute termination of atrial fibrillation or flutter. Class IV drugs are Verapamil and Diltiazem. These drugs are known as nondihydropyridine and act by blocking cardiac calcium uptake. They are used to slow AV nodal conduction by decreasing heart rate. Class V agents include Adenosine, Digoxin, magnesium and sulphate are used in supraventricular arrhyth‐ mias, especially heart failure with atrial fibrillation, contraindicated in patients with ventric‐ ular arrhythmias [1–3]. Amiodarone is considered one of the most effective antiarrhythmic drugs which is widely prescribed. Here, its clinical uses as well as its side effects are reviewed.


**Table 1.** Classification of antiarrhythmic drugs (based on mechanism of action)
