Despite being widely prescribed, acute overdosage with digoxin is uncommon. However, digoxin has a low therapeutic index and toxicity is common. Moreover, toxicity can occur within the 'therapeutic range'; old patients are especially at risk of developing digoxin toxicity.

Toxicity is likely above 2 ng/ml and almost invariable over 3 ng/ml.

If digoxin toxicity is suspected, first measure the plasma potassium; if there is evidence of potassium depletion then withhold digoxin, no matter what the plasma digoxin concentration (1).