Cardiac glycoside

Cardiac glycoside

Cardiac glycoside general structure

• Cardiac glycosides are a class of medications derived from natural sources, primarily plants, that have been used for centuries in the treatment of heart-related conditions.
• These medications exert their effects on the heart by influencing the force and rhythm of cardiac contractions.
• Cardiac glycosides are commonly used in the management of heart failure, atrial fibrillation, and certain arrhythmias.

Mechanism of Action

• The primary mechanism of action of cardiac glycosides is the inhibition of the sodium-potassium adenosine triphosphatase (Na+/K+ ATPase) enzyme, also known as the sodium-potassium pump, located in the cell membrane of cardiac cells.
• This inhibition leads to an increase in intracellular sodium levels and a subsequent decrease in intracellular potassium levels.
• As a result, the intracellular calcium concentration increases via the sodium-calcium exchanger, leading to enhanced myocardial contractility.
• Additionally, cardiac glycosides indirectly influence the autonomic nervous system by increasing vagal tone, which can slow down the heart rate and improve the coordination of atrial contractions.

Classification of Cardiac Glycosides

• Cardiac glycosides can be classified based on their chemical structure and origin.

Here are the main classes of cardiac glycosides:

• Cardenolides:
• Cardenolides are a class of cardiac glycosides that are primarily derived from plants.
• They have a characteristic steroid structure and include the well-known cardiac glycosides digoxin and digitoxin.
• Digoxin, derived from Digitalis purpurea (foxglove), is the most commonly used cardiac glycoside in clinical practice.

• Bufadienolides:
• Bufadienolides are another class of cardiac glycosides that are derived from the skin glands of certain toad species, such as the Bufo genus.
• Examples of bufadienolides include bufalin and cinobufotalin.
• These compounds have a similar mechanism of action to cardenolides and can exhibit cardiac glycoside activity.

• Steroidal Saponins:
• Steroidal saponins are a group of cardiac glycosides that possess a steroid backbone with attached sugar molecules.
• They are primarily derived from various plant sources, including Convallaria majalis (lily of the valley), Urginea maritima (squill), and Strophanthus species.
• Examples of steroidal saponins include convallatoxin, ouabain, and strophanthin.

• The classification of cardiac glycosides is based on their chemical composition and natural sources, reflecting their different origins and structures. Each class may have variations in potency, pharmacokinetics, and clinical use.

Medical Uses

• Cardiac glycosides are primarily used for the treatment of heart failure, atrial fibrillation, and certain arrhythmias.

Their medical uses include:

Heart Failure: Cardiac glycosides improve cardiac function in heart failure by enhancing myocardial contractility and improving cardiac output. They are often prescribed in combination with other heart failure medications, such as diuretics and ACE inhibitors. Atrial Fibrillation: Cardiac glycosides, particularly digoxin, are used to control heart rate in individuals with atrial fibrillation. They help slow down the ventricular response by inhibiting electrical conduction through the atrioventricular node. Arrhythmias: In certain cases, cardiac glycosides can be used to manage specific arrhythmias, such as paroxysmal supraventricular tachycardia (PSVT), atrial flutter, and atrial tachycardia. However, other antiarrhythmic medications are often preferred in these cases.

• The use of cardiac glycosides requires careful monitoring of blood levels and cardiac function, and dosages may need to be adjusted based on individual patient characteristics.

Adverse Effects

• While cardiac glycosides can be effective medications, they are associated with potential adverse effects.

Some common adverse effects of cardiac glycosides include:

Cardiac Effects: Cardiac glycosides can cause arrhythmias, especially if blood levels become excessively high. These arrhythmias may include bradycardia (slow heart rate), atrioventricular block, and ventricular tachycardia. Therefore, careful monitoring of cardiac function and drug levels is essential. Gastrointestinal Disturbances: Gastrointestinal effects, such as nausea, vomiting, and loss of appetite, can occur with the use of cardiac glycosides. Visual Disturbances: Some individuals may experience visual disturbances, such as blurred vision, yellow-green color vision changes, or halos around objects. These effects are more common at higher serum levels and typically resolve with dose adjustments.

• It's crucial to report any concerning symptoms or side effects to a healthcare professional promptly.

Examples of Cardiac Glycosides

The most commonly used cardiac glycoside is:

• Digoxin: Digoxin is derived from the plant Digitalis purpurea (commonly known as foxglove). It has a long history of use in the treatment of heart-related conditions and remains in use today.
• Other cardiac glycosides that have been used in the past, but are less commonly used today, include digitoxin and ouabain.

See Also

• Heart Failure
• Atrial Fibrillation
• Arrhythmias
• Cardiology

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