Digoxin toxicity

What it is

Digoxin toxicity is the clinical state of a patient who either takes digoxin regularly, which is chronic toxicity, or has taken a large dose at once, which is an acute ingestion. It shows up in the rhythm and in AV conduction.

A serum digoxin level within the therapeutic range does not rule out the diagnosis. In the case here the level was within the therapeutic range and the patient was still toxic, because what had changed was how sensitive the heart had become to the drug.

Causes and risk

The risk factors that predispose to chronic digoxin toxicity fall into three groups.

• Increased sensitivity to digoxin: hypokalemia, hyperkalemia and hypomagnesemia, such as from diuretics; hypoxia; and underlying cardiac disease.
• Increased digoxin concentrations: renal insufficiency, which impairs clearance, and any change in renal function; quinidine, quinine and CCBs, which reduce clearance; recent macrolide administration, which reduces the gut flora that metabolizes digoxin, Eubacterium lentum; dehydration; and inhibition of p-glycoprotein, e.g. amiodarone.
• Use of other medications that impair AV conduction: beta-adrenergic antagonists, CCBs and quinine.

In the case here the causes were hypokalemia, with a potassium of 3.1, and dehydration from fasting, with mild renal impairment.