AMIODARONE HYDROCHLORIDE

12.1 Mechanism of Action Amiodarone is considered a class III antiarrhythmic drug, but it possesses electrophysiologic characteristics of all four Vaughan Williams classes. Like class I drugs, amiodarone blocks sodium channels at rapid pacing frequencies, and like class II drugs, amiodarone exerts a noncompetitive antisympathetic action. One of its main effects, with prolonged administration, is to lengthen the cardiac action potential, a class III effect. The negative chronotropic effect of amiodarone in nodal tissues is similar to the effect of class IV drugs. In addition to blocking sodium channels, amiodarone blocks myocardial potassium channels, which contributes to slowing of conduction and prolongation of refractoriness. The antisympathetic action and the block of calcium and potassium channels are responsible for the negative dromotropic effects on the sinus node and for the slowing of conduction and prolongation of refractoriness in the atrioventricular (AV) node. Its vasodila

Contraindications

• • 4 CONTRAINDICATIONS Cardiogenic shock. Sick sinus syndrome
• • second- or third-degree atrioventricular block
• • bradycardia leading to syncope without a functioning pacemaker. Known hypersensitivity to the drug or to any of its components
• • including iodine. Pacerone is contraindicated in patients with ( 4 ): Cardiogenic shock. Sick sinus syndrome
• • second- or third-degree AV block