Digoxin has a narrow therapeutic window and is cleared mainly by the kidneys, so toxicity follows a fall in kidney function, dehydration or a new interacting drug as often as a dose change. In heart failure, lower serum concentrations, around 0.5 to 0.9 ng/mL, are the usual aim.
Hypokalaemia and hypomagnesaemia increase susceptibility, and amiodarone, verapamil and clarithromycin raise levels. Older adults with falling kidney function are the commonest group to tip into toxicity, often presenting with nausea, confusion or a new bradyarrhythmia rather than visual symptoms.
- Take a digoxin level at least six hours after the last dose for an interpretable result.
- Recheck kidney function and potassium when an unwell patient on digoxin is dehydrated or vomiting.
- Reduce the dose or recheck the level when starting amiodarone, verapamil or a macrolide.
- Consider toxicity in an older patient on digoxin with new nausea, confusion or bradycardia.
Why it matters
If stopping digoxin carries risk, keeping it safe matters more than reflexively stopping it.
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