Digoxin

Digoxin: Uses, Dosage and Side Effects

Overview

• An antiarrhythmic.
• Digoxin’s vagomimmetic impact at the AV node decreases atrial fibrillation’s heart rate.
• Delaying AV nodal conduction. Useful in other supraventricular tachyarrhythmias.
• Also mildly inotropic.
• Inhibits Na+–K+ ATPase, raising intracellular sodium. Calcium replaces sodium, increasing intracellular calcium and inotropic action.
• In supraventricular tachyarrhythmias, a reduced heart rate and higher contraction force enhance cardiac output.
• Digoxin improves baroreceptor reflexes that are impaired in heart failure.

Uses of Digoxin

• Management of supraventricular tachyarrhythmias.
• Control the ventricular rate in cases of heart failure with concurrent atrial fibrillation.
• Effective to decrease the ventricular rate in dogs with atrial fibrillation either as monotherapy or in combination with diltiazem.
• Digoxin/diltiazem combination therapy results in more effective rate control than monotherapy.

Dose of Digoxin in Dogs and Cats

Dogs:

• Tablets: 2.5–3.5 μg (micrograms)/kg p.o. q12h based on lean body weight (decrease dose by 10% for elixir).
• Maximum dose 0.25 mg/dog p.o. q12h.
• Start at the lower end of the dose range and up-titrate carefully based on clinical response and serum therapeutic levels.
• Only use i.v. if essentially indicated: 2.2–4.4 μg/kg i.v. q12h.

Cats:

• Tablets: 10 μg (micrograms)/kg p.o. q24–48h, equating to ¼ of a 125 μg tablet q24–48h.
• Start at the lower dose range and titrate up.
• Only use i.v. if essentially indicated: 1–1.6 μg/kg i.v. q12h.

Side Effects of Digoxin in Dogs and Cats

• Dogs are more susceptible to the toxicity of digoxin than cats.
• Hypokalemia predisposes all species to toxicity.
• Anorexia, vomiting, diarrhea, depression, or trigger arrhythmias (such as AV block, bigeminy, paroxysmal ventricular or atrial tachycardias with block, and multiform ventricular premature contractions) are indicators of toxicity.
• Lidocaine and phenytoin may be used to control arrhythmias caused by digoxin.
• Vasoconstriction may be produced by intravenous administration.

Contraindications of Digoxin in Dogs and Cats

• Frequent atrioventricular block or ventricular arrhythmias.
• Regarded as contraindicated in feline hypertrophic cardiomyopathy cases.
• Do not use it in the presence of hypokalemia.

Some Notes:

• Antacids, chemotherapy drugs (e.g., cyclophosphamide, cytarabine, doxorubicin, vincristine), cimetidine, and metoclopramide may inhibit digoxin absorption from the gastrointestinal tract.
• Amiodarone, antimuscarinics, diazepam, erythromycin, loop and thiazide diuretics (hypokalemia), oxytetracycline, and verapamil may increase the serum concentration, decrease the elimination rate, or exacerbate the toxic effects of digoxin.
• Spironolactone may exacerbate or mitigate the toxicity of digoxin.