Class II anti-arrhythmic drugs: β-blockers and sotalol
THE CONTEXT
Class II drugs are β-adrenoceptor antagonists with nodal effects that support rate control and arrhythmia prevention.
Actions and clinical benefits
•
β-blockers reduce the rate of SA node depolarisation and cause relative AV nodal block, making them useful for rate control in atrial flutter and atrial fibrillation.
•
They can prevent ventricular and supraventricular tachycardia.
•
They reduce myocardial excitability and the risk of arrhythmic death in patients with coronary artery disease and heart failure.
Non-selective and cardioselective agents
•
Non-selective β-blockers act on both β1 and β2 receptors. β2 blockade can cause bronchospasm and peripheral vasoconstriction.
•
Propranolol is non-selective and undergoes extensive hepatic first-pass metabolism. Its effective oral dose is unpredictable, so treatment starts with a small dose and is subsequently titrated.
•
Nadolol and carvedilol are other non-selective agents.
•
Cardioselective β-blockers act mainly on myocardial β1 receptors and are relatively well tolerated. Examples are bisoprolol and metoprolol.
Sotalol
•
Sotalol is a racemic mixture with non-selective β-blocker activity mainly attributable to l-sotalol and class III activity mainly attributable to d-sotalol.