Digoxin

Digoxin is a cardiac glycoside with positive inotropic and atrioventricular nodal effects. Its major contemporary veterinary role is ventricular rate control in selected supraventricular tachyarrhythmias, particularly atrial fibrillation. It also has an adjunctive role in some heart-failure treatment plans, although other agents are more commonly chosen for primary inotropic support.

Group

Cardiac glycoside

Mechanism of Action

Digoxin inhibits myocardial sodium–potassium ATPase, increasing intracellular sodium and reducing calcium removal through sodium–calcium exchange. Increased intracellular calcium availability strengthens cardiac contraction. It also increases vagal influence and modifies autonomic signaling, slowing atrioventricular nodal conduction and increasing nodal refractoriness. This reduces the number of atrial impulses reaching the ventricles during selected supraventricular arrhythmias.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Cardiac rate control	0.005–0.011 mg/kg	PO	Every 12 h	Lean body weight; elixir may require a 10% lower amount.
Cardiac rate control	0.005–0.01 mg/kg	PO	Every 12 h	Alternative regimen specifically for dogs under 20 kg.
Large-dog cardiac rate control	Reference only	PO		Dogs over 20 kg: 0.22 mg/m² every 12 hours; reduce 10% for elixir. BSA calculation required.
Rapid digitalization — Loading	0.0055–0.011 mg/kg	IV	Every 1 h	Titrate to effect under ECG and concentration monitoring.
Atrial fibrillation	0.005 mg/kg	PO	Every 12 h	May be combined with diltiazem 3 mg/kg every 12 hours.
Atrial fibrillation with heart failure	0.005–0.0075 mg/kg	PO	Every 12 h	Normal renal function; target trough 0.8–1.2 ng/mL.
Dilated cardiomyopathy with atrial fibrillation	0.0025 mg/kg	PO	Every 12 h	Loading usually omitted; extra caution with ventricular arrhythmias. Target trough 0.8–1.2 ng/mL.
Atrial fibrillation	0.003–0.005 mg/kg	PO	Every 12 h

Cat

Use / stage	Dose	Route	Schedule	Instructions
Cardiac rate control	0.008–0.01 mg/kg	PO	Every 48 h

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Cardiac support — Loading	22 mcg/kg	IV
Cardiac support — Maintenance	0.86 mcg/kg/hour	IV	Continuous
Cardiac support — Maintenance	3.4 mcg/kg	IV	Every 4 h	Intermittent alternative to continuous infusion.

Horse

Use / stage	Dose	Route	Schedule	Instructions
Cardiac support	2 mcg/kg	IV	Every 12 h
Cardiac support	15 mcg/kg	PO	Every 12 h

Ferret

Use / stage	Dose	Route	Schedule	Instructions
Dilated cardiomyopathy — Initial	0.01 mg/kg	PO	Every 24 h	Oral liquid; increase to twice daily only after response assessment.
Heart failure — Maintenance	0.005–0.01 mg/kg	PO	Every 12–24 h	Monitor serum digoxin and potassium.

Hamster

Use / stage	Dose	Route	Schedule	Instructions
Dilated cardiomyopathy	0.05–0.1 mg/kg	PO	Every 12 h

Indications

Control of ventricular rate in dogs with atrial fibrillation, often in combination with another atrioventricular nodal blocking agent.
Rate control in selected other supraventricular tachyarrhythmias in dogs and other veterinary patients.
Adjunctive treatment of selected congestive heart-failure patients requiring its combined neurohormonal, rate-control or inotropic effects.

Contraindications

Narrow therapeutic index; heightened sensitivity in cats and some Dobermans.

Interactions

Hypokalemia increases toxicity.
Quinidine, macrolides and other inhibitors can raise exposure.
Beta blockers and calcium-channel blockers increase AV-block risk.
Phenobarbital may lower exposure.

Adverse effects

Arrhythmias and AV block
Vomiting, anorexia and diarrhea

Toxicity

Gastrointestinal signs may precede serious arrhythmias; stop treatment and assess concentration, potassium and cardiac rhythm.

Preparations

Preparation	Form	Strength	Route
Digoxin 0.0625 mg	Tablet	0.0625 mg / tablet	PO
Digoxin 0.125 mg	Tablet	0.125 mg / tablet	PO
Digoxin 0.25 mg	Tablet	0.25 mg / tablet	PO
Digoxin elixir 0.05 mg/mL	Oral Liquid	0.05 mg / mL	PO
Digoxin elixir 0.15 mg/mL	Oral Liquid	0.15 mg / mL	PO

Monitoring and Administration

Calculate using lean body weight. Elixir doses may need a 10% reduction compared with tablets.

Monitor ECG, renal function, electrolytes and serum concentration 8–10 hours after dosing; a commonly used target is 0.8–1.5 ng/mL.

Avoid mixing tablets with other medicines when compounding and avoid very acidic solutions.

The additional avian regimen omits its route and ranges from 0.02–0.5 mg/kg every 12 hours initially, then 0.01 mg/kg every 12–24 hours. This very wide, incompletely specified regimen is not a calculable prescription.