digoxin: clinical use

Prescribing considerations

• Individualise treatment according to indication, age, lean body weight, renal function, thyroid status, electrolytes and interacting medicines.
• Reduced renal clearance, advancing age and electrolyte disturbance increase susceptibility to toxicity.
• Review the clinical context rather than relying on serum concentration alone; toxicity can occur within the laboratory reference range.
• Exercise particular caution around electrical cardioversion where digitalis toxicity is possible.

Contraindications and cautions

• Intermittent complete heart block or second-degree atrioventricular block, particularly with previous Stokes–Adams attacks.
• Arrhythmias caused by cardiac glycoside toxicity.
• Ventricular tachycardia or ventricular fibrillation.
• Supraventricular arrhythmia associated with a known or suspected accessory atrioventricular pathway, unless appropriately evaluated.
• Hypertrophic obstructive cardiomyopathy, except selected cases with concomitant atrial fibrillation and heart failure, where caution remains necessary.
• Hypersensitivity to digoxin, another digitalis glycoside or a formulation excipient.

Monitoring

• Assess renal function, potassium, magnesium, calcium and thyroid function before treatment and periodically thereafter.
• Increase monitoring with renal impairment, older age, acute illness or relevant interacting medicines.
• Routine serum digoxin measurement is generally unnecessary once stable; consider it for suspected toxicity, altered renal function, thyroid disease, adherence concerns or important interactions.
• Take serum samples only after distribution is sufficiently complete and interpret results alongside symptoms, ECG, renal function and electrolytes.

Clinical pharmacology

Digoxin inhibits sodium–potassium ATPase, increasing intracellular calcium and myocardial contractility. It increases vagal tone and slows atrioventricular nodal conduction. It has a large tissue distribution and is eliminated mainly unchanged through the kidneys; P-glycoprotein affects intestinal absorption and renal elimination.

Formulation and product differences

• Tablets and oral solution are not directly bioequivalent; the oral solution has greater bioavailability, so formulation changes require clinical review.
• The oral solution must be measured with its graduated pipette and not diluted; it contains sucrose and other excipients relevant to some patients.
• The tablet formulation contains lactose.
• The injection contains ethanol, is intended for intravenous use by healthcare professionals and should not be administered intramuscularly.

Oral solution

Route: Oral

Strengths: 0.05 mg/mL

Tablet

Route: Oral

Strengths: 62.5 micrograms, 125 micrograms, 250 micrograms