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Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers

Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers

Class I antiarrhythmic drugs are used to treat various types of arrhythmias or irregular heart rhythms. These drugs block the sodium (Na+) channels in the cardiac cells, thereby affecting the movement of electrical impulses across the heart. Class I antiarrhythmic drugs are divided into three subgroups: Class IA, Class IB, and Class IC, each with distinct mechanisms of action and effects on the heart.
Class 1A Antiarrhythmic Drugs: These drugs work by moderately blocking sodium channels,...

Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers

Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers

Adrenergic stimulation generally impacts cardiac rate and rhythm. Specifically, stimulation of the β-adrenoceptors triggers an increase in intracellular calcium ion influx and pacemaker currents, which may cause arrhythmias. Catecholamines like adrenaline also demonstrate β2-adrenoceptor-mediated hypokalemia, impacting cardiac action potential and disrupting the normal cardiac rhythm. Class II antiarrhythmic drugs are β-adrenoceptor antagonists or β-blockers, which...

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

Class III antiarrhythmic drugs are a group of medications that can prolong action potentials in the heart. They achieve this by blocking potassium channels or enhancing inward currents from sodium channels. However, these drugs have a unique property of "reverse use-dependence," which is most pronounced at slower heart rates and can lead to torsades de pointes—a specific type of arrhythmia. However, it is essential to note that excessive QT interval prolongation—a measure of...

Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers

Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers

Class IV antiarrhythmic drugs, such as verapamil and diltiazem, block calcium channels. They primarily affect the heart, slowing the conduction in calcium-dependent tissues like the SA and AV nodes. These drugs manage reentrant supraventricular tachycardia (SVT) and reduce ventricular rate in atrial flutter/fibrillation.
Verapamil, a calcium channel blocker, inhibits calcium movement across myocardial cell membranes and vascular smooth muscle. This results in the dilation of coronary and...

Heart Failure Drugs: Inotropic Agents

Heart Failure Drugs: Inotropic Agents

Positive inotropic agents are commonly used as the first line of treatment for heart failure. One such agent is digoxin, derived from the genus Digitalis, which has been known for centuries but effectively utilized since 1785. However, these cardiac glycosides can have potentially toxic effects due to their mechanism of action, which involves inhibiting Na+/K+-ATPase and increasing contractility. Digoxin is absorbed orally and distributed in various tissues, including the CNS. It has a long...

Drug Toxicity: Risk factors

Drug Toxicity: Risk factors

Adverse Drug Reactions (ADRs) are potential complications that arise during pharmacotherapy, influenced by multiple risk factors. Age plays a significant role; both neonates and the elderly are at heightened risk due to their respective immature and diminished metabolic and elimination processes. Gender also impacts ADRs, with females experiencing a 1.5 to 1.7-fold greater risk than males, which may be linked to pharmacokinetic, pharmacodynamic, and hormonal differences. Notably, neonates, the...

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Related Experiment Video

Updated: May 3, 2026

Percutaneous Contrast Echocardiography-guided Intramyocardial Injection and Cell Delivery in a Large Preclinical Model

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Amiodarone pulmonary toxicity

F E Marchlinski, T S Gansler, H L Waxman

Annals of Internal Medicine

|December 1, 1982

Summary

Amiodarone hydrochloride therapy can cause pulmonary toxicity, presenting with respiratory symptoms and lung abnormalities. Stopping the drug and using corticosteroids can resolve these issues, though the exact role of steroids is unclear.

Area of Science:

Pulmonology
Pharmacology
Toxicology

Background:

Amiodarone hydrochloride is an antiarrhythmic drug.
Pulmonary toxicity is a known adverse effect of amiodarone therapy.

Observation:

Clinical presentation includes dyspnea, leukocytosis, hypoxemia, elevated ESR, and restrictive pulmonary function tests.
Radiographic findings show interstitial and alveolar infiltrates, often in upper lobes.
Histology reveals foamy macrophages, type II pneumocyte hyperplasia, and widened septa.

Findings:

Ultrastructural analysis shows lysosomal abnormalities.
Cessation of amiodarone and corticosteroid treatment lead to resolution of symptoms and radiographic changes.
Radiographic resolution may take over two months.

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Implications:

Pulmonary toxicity from amiodarone is treatable with drug cessation and corticosteroids.
The underlying mechanism may be metabolic rather than immunologic, warranting further investigation.
Early recognition and management are crucial for patient outcomes.