Digoxin

How it works

It inhibits the myocardial sodium-potassium ATPase, raising intracellular calcium to increase contractility, and enhances vagal tone to slow atrioventricular conduction.

Prescribing in practice

• Older patients are highly susceptible to toxicity because of declining renal function and low body mass, so use lower doses, account for renal impairment, and recognise that hypokalaemia, hypomagnesaemia and hypercalcaemia potentiate toxicity.
• Many interacting drugs (including amiodarone, verapamil, diuretics and macrolides) raise levels or precipitate toxicity, so review co-prescriptions carefully.
• Toxicity may present atypically as confusion, nausea, anorexia, visual disturbance or new arrhythmia.

Monitoring

Monitor renal function and electrolytes (particularly potassium), heart rate and clinical response, with digoxin level measurement guided by symptoms and taken at an appropriate interval after dosing.

Counselling the patient

• Report nausea, loss of appetite, confusion, visual changes or palpitations, which can signal toxicity.
• Do not stop or change the dose without advice, and keep regular blood tests.
• Tell clinicians about all new medicines, as many interact with digoxin.

Evidence & guidelines

Long-standing trial and registry data support digoxin for rate control and symptom relief, while pharmacokinetic principles underpin cautious dosing and monitoring in older patients with reduced renal reserve.