Pharmacology of Drugs for Heart Failure

Digoxin: Indications, Mechanism, and Toxicity

Digoxin is a cardiac glycoside used in the treatment of heart failure and atrial fibrillation. Its primary mechanism involves inhibition of the Na+/K+-ATPase pump, leading to increased intracellular calcium and enhanced myocardial contractility.

Indications

• Heart failure with reduced ejection fraction (HFrEF)
• Atrial fibrillation with rapid ventricular response
• Control of heart rate in specific arrhythmias

Mechanism of Action

Digoxin binds to and inhibits the Na+/K+-ATPase pump in cardiac cells. This leads to an increase in intracellular sodium, which subsequently promotes calcium influx through the sodium-calcium exchanger, resulting in stronger cardiac contractions.

Toxicity and Side Effects

• Gastrointestinal disturbances (nausea, vomiting, diarrhea)
• Neurological effects (confusion, dizziness, visual disturbances)
• Cardiac arrhythmias (bradycardia, ventricular tachycardia, fibrillation)
• Electrolyte imbalances (hypokalemia increases toxicity risk)

Management of Digoxin Toxicity

• Discontinuation of digoxin
• Correction of electrolyte imbalances (particularly potassium and magnesium)
• Administration of digoxin-specific antibody (Digibind) in severe cases
• Continuous cardiac monitoring

Conclusion

Digoxin remains a valuable agent for managing heart failure and atrial fibrillation, but its narrow therapeutic window necessitates careful monitoring to prevent toxicity.