How the dose is calculated
The total loading (digitalizing) dose is estimated at roughly 12 mcg/kg — the midpoint of the commonly cited 10-15 mcg/kg range — conventionally split as approximately half now, then a quarter at 6-8 hours, then the final quarter a further 6-8 hours later. The maintenance dose is estimated at 4 mcg/kg/day with normal renal function, halved for significant renal impairment since digoxin is predominantly renally cleared.
Typical dosing
| Normal renal function | Significant renal impairment | |
|---|---|---|
| Loading (total) | ~12 mcg/kg, divided over ~24h | |
| Maintenance | ~4 mcg/kg/day | ~2 mcg/kg/day |
Clinical use
- Digoxin is used for rate control in atrial fibrillation/flutter (particularly where beta-blockers or calcium channel blockers are poorly tolerated) and, less commonly now, in heart failure with reduced ejection fraction for symptom control.
- Target trough serum digoxin level is typically 0.5-0.9 ng/mL for heart failure indications — levels should be drawn at least 6 hours after a dose (ideally just before the next dose) to avoid a falsely high reading from the distribution phase.
- Correct hypokalaemia, hypomagnesaemia, and hypercalcaemia before/during digoxin therapy — each independently increases the risk of digoxin toxicity at a given serum level.
- Numerous drug interactions increase digoxin levels (e.g. amiodarone, verapamil, clarithromycin) — review the full medication list before initiating or adjusting the dose.
Frequently asked questions
What is the loading dose of digoxin?
Approximately 10-15 mcg/kg total, conventionally divided as roughly half now, a quarter at 6-8 hours, and the final quarter a further 6-8 hours later, with clinical/ECG monitoring throughout.
Why is digoxin dosed differently in renal impairment?
Digoxin is predominantly cleared by the kidneys, so reduced renal function leads to drug accumulation and a higher risk of toxicity at a "normal" dose — the maintenance dose is reduced (and sometimes the interval extended) accordingly, guided by renal function and, where possible, serum level monitoring.
What are the signs of digoxin toxicity?
Nausea, vomiting, and anorexia are common early symptoms; visual disturbances (blurred vision, yellow-green halos) are classic but not universal; cardiac toxicity can present as almost any arrhythmia, including bradycardia, heart block, and ventricular arrhythmias — any new arrhythmia in a patient on digoxin should prompt a level check.
When should a digoxin level be checked?
At least 6 hours after the last dose (ideally as a trough, just before the next dose) — checking too soon after a dose captures the distribution phase and gives a falsely high result that doesn't reflect steady-state tissue levels.
References
- British National Formulary (BNF) — Digoxin.
- Tripathi KD. Essentials of Medical Pharmacology, 8th edition — Cardiac glycosides.