Class III antiarrhythmic

Class III Antiarrhythmic

Class III antiarrhythmic drugs are a category of medications used to treat irregular heartbeats, known as arrhythmias. These drugs primarily work by blocking potassium channels in the heart, which prolongs the repolarization phase of the cardiac action potential. This action helps to stabilize the heart rhythm and prevent abnormal electrical activity that can lead to arrhythmias.

Mechanism of Action

Class III antiarrhythmics exert their effects by inhibiting the efflux of potassium ions during the repolarization phase of the cardiac action potential. This results in a prolonged action potential duration and an increased refractory period. By extending the refractory period, these drugs reduce the likelihood of reentrant arrhythmias, which are a common cause of tachycardia.

Common Class III Antiarrhythmic Drugs

• Amiodarone: One of the most widely used Class III antiarrhythmics, amiodarone is effective in treating a variety of arrhythmias, including atrial fibrillation and ventricular tachycardia. However, it has a complex side effect profile and can affect multiple organ systems.

• Sotalol: This drug has both beta-blocking and Class III antiarrhythmic properties. It is used to treat ventricular arrhythmias and to maintain sinus rhythm in patients with atrial fibrillation.

• Dofetilide: A pure Class III antiarrhythmic, dofetilide is used primarily for the conversion and maintenance of sinus rhythm in patients with atrial fibrillation or atrial flutter.

• Ibutilide: Used for the acute conversion of atrial fibrillation and atrial flutter to sinus rhythm, ibutilide is administered intravenously.

Clinical Uses

Class III antiarrhythmics are used in the management of various types of arrhythmias, including:

• Atrial fibrillation
• Atrial flutter
• Ventricular tachycardia
• Ventricular fibrillation

These drugs are often chosen when other antiarrhythmic classes are ineffective or contraindicated.

Side Effects

The use of Class III antiarrhythmics can be associated with several side effects, including:

• Torsades de Pointes: A specific type of polymorphic ventricular tachycardia that can be life-threatening.
• Pulmonary toxicity: Particularly with amiodarone, which can cause pulmonary fibrosis.
• Thyroid dysfunction: Amiodarone can cause both hypothyroidism and hyperthyroidism.
• Hepatotoxicity: Liver function should be monitored during treatment.

Also see

• Class I antiarrhythmic
• Class II antiarrhythmic
• Class IV antiarrhythmic
• Arrhythmia
• Cardiac action potential

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