Cardiotonic agent

Drugs that increase the efficiency of the heart

Cardiotonic agents are a class of medications that increase the contractility of the heart muscle, thereby improving cardiac output. These agents are primarily used in the treatment of heart failure and certain types of arrhythmia.

Mechanism of Action

Cardiotonic agents work through various mechanisms to enhance the heart's pumping ability. The main types of cardiotonic agents include cardiac glycosides, beta-adrenergic agonists, phosphodiesterase inhibitors, and calcium sensitizers.

Cardiac Glycosides

Mechanism of action of cardiac glycosides

Cardiac glycosides, such as digoxin, inhibit the sodium-potassium pump (Na⁺/K⁺-ATPase) in cardiac cells. This inhibition leads to an increase in intracellular sodium, which in turn affects the sodium-calcium exchanger, resulting in increased intracellular calcium. The elevated calcium levels enhance myocardial contractility.

Beta-Adrenergic Agonists

Mechanism of action of beta-adrenergic agonists

Beta-adrenergic agonists, such as dobutamine, stimulate beta-1 adrenergic receptors on cardiac myocytes. This stimulation increases cyclic AMP (cAMP) levels, which enhances calcium influx into the cells, thereby increasing contractility.

Phosphodiesterase Inhibitors

Mechanism of action of phosphodiesterase inhibitors

Phosphodiesterase inhibitors, such as milrinone, prevent the breakdown of cAMP by inhibiting the enzyme phosphodiesterase. The increased cAMP levels lead to enhanced calcium entry into the cardiac cells, improving contractility.

Calcium Sensitizers

Mechanism of action of calcium sensitizers

Calcium sensitizers, such as levosimendan, increase the sensitivity of cardiac myofilaments to calcium, thereby enhancing contractility without increasing intracellular calcium levels. This mechanism reduces the risk of calcium overload and arrhythmias.

Clinical Use

Cardiotonic agents are primarily used in the management of heart failure, particularly in cases where there is reduced ejection fraction. They are also used in certain types of arrhythmias, such as atrial fibrillation, to control heart rate and improve cardiac output.

Side Effects

The use of cardiotonic agents can be associated with several side effects, including arrhythmias, gastrointestinal disturbances, and electrolyte imbalances. Monitoring of drug levels and electrolytes is essential during therapy.

Related Pages

• Heart failure
• Arrhythmia
• Digoxin
• Dobutamine
• Milrinone
• Levosimendan