How Do Class III Antidysrhythmics Work?
WHAT ARE CLASS III ANTIDYSRHYTHMICS AND HOW DO THEY WORK?
Antidysrhythmics, also known as antiarrhythmics, are drugs used to prevent abnormal cardiac rhythms such as atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation caused by improper conduction of impulses in the heart. They work by blocking sodium, potassium, and calcium channels in the heart muscles.
Antiarrhythmic drugs are grouped into four main classes:
- Class I, sodium-channel blockers;
- Class II, beta-blockers;
- Class III, potassium-channel blockers;
- Class IV, calcium-channel blockers; and
- miscellaneous antiarrhythmics or unclassified antiarrhythmics.
Class III antidysrhythmic drugs work by inhibiting delayed rectifier potassium currents. The characteristic action of this class is the prolongation of repolarization. They prolong action potential duration, increase effective refractory period (resting state in a depolarized cardiac cell), and widen QT interval. They have no effect on conduction velocity.
Antidysrhythmic drugs do not improve the survival rate among patients with nonlife-threatening arrhythmias and may increase mortality in patients with structural heart disease.
HOW ARE CLASS III ANTIDYSRHYTHMICS USED?
Class III antidysrhythmic drugs are used to treat:
- Supraventricular arrhythmias (abnormal heartbeats that originate above the lower chambers of the heart)
- Ventricular arrhythmias (abnormal heartbeats that originate in the lower heart chambers)
- Atrial fibrillation and flutter (rapid and irregular heartbeats in the upper chamber of the heart)
WHAT ARE SIDE EFFECTS OF CLASS III ANTIDYSRHYTHMICS?
Serious side effects of class III antidysrhythmics include:
- QT prolongation (heart muscle takes longer than usual to recover after each beat)
- Heart failure
- Heart block (an abnormal heart rhythm where the heart beats too slowly)
- Bradycardia (slow heart rate)
- Ventricular tachycardia (rapid increase in heartbeat in the lower two chambers of the heart)
- Lung fibrosis (lung tissue is damaged and thickened)
- Hepatotoxicity (deterioration in liver function because of the poisonous effect of the drug)
- Neurotoxicity
- Cardiotoxicity
- Corneal deposition and cause blindness
- Blue skin syndrome (pigmentation of facial skin caused by amiodarone)
The other common side effects include:
- Constipation
- Photosensitivity (sensitivity to sunlight)
- Photodermatitis (skin allergy caused when exposed to sunlight)
- Hyperthyroidism (excessive production of thyroxine hormone by the thyroid gland)
- Hypothyroidism (less production of thyroxine hormone by the thyroid gland)
- Fatigue
- Dizziness
- Breathlessness
The information contained herein is not intended to cover all possible side effects, precautions, warnings, drug interactions, allergic reactions, or adverse effects. Check with your doctor or pharmacist to make sure these drugs do not cause any harm when you take them along with other medicines. Never stop taking your medication and never change your dose or frequency without consulting your doctor.
