The ancient Egyptians and Romans once used cardiac glycosides as arrow poisons by African tribes and as medicines. Their value in treating heart disorders has been known for over 2,000 years. It is extracted from the flowering plant Digitalis purpurea and Digitalis lanata, drugs from this class also called as digitalis glycosides. DIGOXIN is the only drug in this class available in the USA.
Mechanism of action:
The primary actions of digoxin are to cause the heart to beat more forcefully and more slowly, thus improving cardiac output. It has mechanical effects as it increases myocardial contractility; however, the duration of the contractile response is just slightly increased. Overall, the heart rate is decreased, while blood pressure increases as the stroke volume is increased, leading to increased tissue perfusion. Myocardial efficiency improves due to improve hemodynamic, and the ventricular function curve is improved.
Digoxin binds to a site on the extracellular aspect of the α-subunit of the Na+/K+ ATPase pump in the membranes of heart cells (myocytes) and decreases its function. This causes an increase in the level of sodium ions in the myocytes, which leads to a rise in the level of intracellular calcium ions. This occurs because of a sodium/calcium exchanger on the plasma membrane, which depends on a constant inward sodium gradient to pump out calcium. Digoxin decreases sodium concentration gradient and the subsequent calcium outflow, thus raising the calcium concentration in myocardiocytes and pacemaker cells.
Digoxin also suppresses the impulse conduction in the heart by SA node and slow electrical conduction through AV node.
- Atrial fibrillation
- Atrial flutter
- Congestive heart failure with congestion of other drugs like Diuretics, and ACE inhibitors
- Cardiac Dysrhythmias
- Visual disturbances
- Dysrhythmias especially in client with Hypokalemia and renal diseases
- Digoxin + Diuretics =Hypokalemia can cause Dysrhythmias
- Digoxin + ACE inhibitors, spironolactone, or potassium sparing diuretics = Hyperkalemia and reduce therapeutic action of digoxin
- Digoxin + other inotropic drugs = increased heart contractility
digoxin + beta blockers = additive bradycardia
- Digoxin + antacids or lipid lowering drugs = decrease absorption of digoxin
- Digoxin + IV calcium = risk for Dysrhythmias
- Digoxin + verapamil, amiodarone, and alprazolam = decrease distribution and excretion of digoxin and increase the effects of digoxin
DIGOXIN OVERDOSE CAN BE FATAL. SPECIFIC THERAPY INVOLVES IV INFUSION OF DIGOXIN IMMUNE AB , WHICH CONTAIN ANTIBODIES SPECIFIC FOR DIGOXIN.