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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.
The difference between toxicity and therapeutic range is small for digoxin and is determined to be between 0.5-2 ng/mL (2)
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)
Severe toxicity requires hospital admission and consideration of the need for digoxin-specific antibody fragments