Class 4 Antiarrhythmic Drugs: Verapamil and Diltiazem

Verapamil

Mechanism of Action

• Blocks both activated and inactivated L-type calcium channels.
• More effective in tissues that fire frequently or are less completely polarized at rest, such as the SA and AV nodes.
• Can suppress both early and delayed afterdepolarizations.

Extracardiac Effects

• Causes peripheral vasodilation, which is beneficial in hypertension and peripheral vasospastic disorders.

Toxicity

• Cardiotoxic effects are dose-related and usually avoidable.
• Can induce AV block in large doses or in patients with AV nodal disease.
• Adverse extracardiac effects include constipation, lassitude, nervousness, and peripheral edema.

Pharmacokinetics & Dosage

• Half-life of 4–7 hours.
• Extensively metabolized by the liver; bioavailability is only about 20% after oral administration.
• Dosage varies depending on the route of administration and the condition being treated.

Therapeutic Use

• Major indication is for supraventricular tachycardia.
• Can also reduce the ventricular rate in atrial fibrillation and flutter (“rate control”).

Diltiazem

Mechanism of Action

• Similar in efficacy to verapamil for managing supraventricular arrhythmias.

Toxicity

• Causes hypotension or bradyarrhythmias relatively infrequently.

Therapeutic Use

• Used in the management of supraventricular arrhythmias, including rate control in atrial fibrillation.
• An intravenous form is available for rate control in atrial fibrillation.

Conclusion

Class 4 antiarrhythmic drugs like Verapamil and Diltiazem primarily act by blocking calcium channels, which makes them effective in treating supraventricular arrhythmias. However, they come with their own set of risks and side effects, including the potential for cardiotoxicity in certain conditions. Therefore, their use should be carefully considered and monitored.

Note: This article is intended for educational purposes and should not be considered as medical advice. Always consult with a healthcare professional for medical advice and treatment.