Digitoxin

Digitoxin is a cardiac glycoside used for the treatment of heart failure and certain kinds of heart arrhythmia. It is a phytosteroid and is similar in structure and effects to digoxin, though the effects are longer-lasting. Unlike digoxin, which is eliminated from the body via the kidneys, it is eliminated via the liver, and so can be used in patients with poor or erratic kidney function. While several controlled trials have shown digoxin to be effective in a proportion of patients treated for heart failure, the evidence base for digitoxin is not as strong, although it is presumed to be similarly effective. Digitoxin is used for the treatment of heart failure, especially in people with impaired kidney function. It is also used to treat certain kinds of heart arrhythmia, such as atrial fibrillation. Contraindications include problems with the heart rhythm, such as severe bradycardia (slow heartbeat), ventricular tachycardia (fast heartbeat caused by the ventricles), ventricular fibrillation, or first- to second-degree atrioventricular block, and certain electrolyte imbalances: hypokalemia (low blood potassium levels), hypomagnesemia (low magnesium), and hypercalcemia (high calcium). Digitoxin exhibits similar toxic effects to digoxin, namely: anorexia, nausea, vomiting, diarrhea, confusion, visual disturbances, and cardiac arrhythmias. Antidigoxin antibody fragments, the specific treatment for digoxin poisoning, are also effective in serious digitoxin toxicity. Drugs that can increase digitoxin toxicity include: calcium substances that lower potassium or magnesium levels, such as diuretics and corticosteroids inhibitors of the liver enzyme CYP3A4, which slow down digitoxin metabolism; examples are the antibiotic clarithromycin, the antifungal itraconazole, and grapefruit juice inhibitors of the transporter protein P-gp, such as clarithromycin Beta blockers add to the bradycardia (slow heartbeat) caused by digitoxin.