Digoxin: The Dispensing Safety Checklist

📋 First Dispense Essentials

Mandatory items to issue

• Confirm the indication: atrial fibrillation (AF) or heart failure. Record the indication, dose, and formulation on the pharmacy medication record.
• Confirm baseline blood tests have been completed before starting treatment: urea and electrolytes (U&E) including potassium and sodium, serum creatinine, calcium, magnesium, and thyroid function tests.
• Explain blood sampling requirements to the patient: serum digoxin levels must be taken no less than 6 hours after the last dose, and ideally 8 to 12 hours after. Earlier samples give falsely elevated results. Blood samples taken at the wrong time are a common source of unnecessary dose reductions.

Baseline clinical checks

• Serum potassium: low potassium greatly increases the risk of digoxin toxicity and can cause serious arrhythmias even when the digoxin level appears normal.
• Serum magnesium: hypomagnesaemia also predisposes to toxicity. Long-term use of proton pump inhibitors (PPIs) is a recognised cause of low magnesium and should prompt more frequent monitoring.
• Calcium: hypercalcaemia increases digoxin toxicity risk. Hypocalcaemia may indicate low magnesium.
• Renal function: digoxin is largely cleared by the kidneys. Even a modest decline in kidney function can cause levels to rise rapidly.
• Thyroid function: hypothyroidism increases sensitivity to digoxin and may require a lower dose. Hyperthyroidism causes relative resistance, and the dose may need to be higher. Thyroid status should be reassessed whenever digoxin appears ineffective or unexpectedly toxic.

Key risks and lifestyle traps

• Amiodarone can substantially increase digoxin concentrations by inhibiting renal excretion. When amiodarone is started, confirm that the prescriber has reviewed the digoxin dose and arranged a monitoring plan. This interaction is frequently missed when patients are started on amiodarone in hospital and discharged without a digoxin review.
• Verapamil and diltiazem both raise digoxin levels and cause additive slowing of the heart rate and atrioventricular (AV) conduction. If either is newly prescribed alongside digoxin, monitor closely for bradycardia and signs of toxicity.
• Loop diuretics (furosemide) and thiazide diuretics cause hypokalaemia, which potentiates digoxin toxicity. Many patients on digoxin are also on diuretics: potassium levels must be checked regularly and any falls acted upon promptly.
• Spironolactone inhibits the renal tubular secretion of digoxin and raises levels. A dose change in spironolactone should prompt vigilance for toxicity signs.
• Macrolide antibiotics (erythromycin, clarithromycin) can increase digoxin levels in some patients by eradicating gut bacteria that normally inactivate digoxin before absorption. This is unpredictable and patients should be counselled to report toxicity symptoms during any macrolide course.
• Serum digoxin levels are NOT checked routinely. Digoxin levels should not be interpreted in isolation: toxicity can occur at concentrations within the accepted range, particularly in older patients, those with renal impairment, or when potassium is low. Check a level when toxicity is suspected, renal function has deteriorated, a new interacting medicine has been started, or after a dose change (7 days post-change).
• St John's Wort induces P-glycoprotein and can reduce digoxin concentrations, potentially reducing efficacy. Check for herbal medicines and supplements at every dispense.

First dispense script

🔄 Repeat Dispense Screen

Mandatory documentation

• Record the dose and formulation dispensed on every occasion. Note any dose changes and the reason.
• Record whether electrolyte and renal function monitoring appears current. Document any interventions made if monitoring appears overdue.
• Note any newly started or recently stopped interacting medicines.

Ongoing clinical checks

• Urea and electrolytes (including potassium) and renal function: at least annually, and more frequently in elderly patients, those with renal impairment, or those on diuretics. Consider magnesium monitoring in patients at higher risk of deficiency, including those on long-term proton pump inhibitors.
• Thyroid function: annually. Thyroid status affects digoxin requirements and can change over time.
• Serum digoxin level: not required routinely. Check if toxicity is suspected, renal function has deteriorated, a new interacting medicine has been started, or 7 days after any dose change.
• Check for any newly prescribed interacting medicines, especially amiodarone, verapamil, diltiazem, spironolactone, diuretics, and macrolide antibiotics.

Ask the patient at the counter

• "Have you noticed any nausea, loss of appetite, vomiting, or changes in your vision, particularly blurring or seeing yellow or green around lights?"
• "Has your heart felt very slow, or have you noticed an irregular heartbeat?"
• "Have you started any new medicines or had any change to your existing medicines recently?"

Lifestyle and surgical alerts

• Dehydration raises digoxin levels. During illness with vomiting, diarrhoea, or reduced fluid intake, patients should seek advice from their prescriber promptly.
• Any significant change in kidney function, including following acute illness or surgery, may require a digoxin dose review and level check.
• Patients should not stop digoxin suddenly without prescriber advice. Loss of rate control may follow abrupt discontinuation in atrial fibrillation.

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