Digoxin toxicity with normal digoxin and serum potassium levels: beware of magnesium, the hidden malefactor

In recent years, digoxin use has been on the decline, with decreased incidence of digoxin toxicity. Hence, digoxin toxicity, when it occurs, remains an elusive diagnosis to emergency physicians.

To present a case of digoxin toxicity with normal levels of digoxin and serum potassium, but with severe hypomagnesemia.

A 66-year-old woman presented with junctional tachycardia and ectopic atrial tachycardia. She was known to have congestive cardiac failure on diuretic therapy. Her serum digoxin level was within the normal range (2.4 nmol/L [normal = 1.9-2.6]) along with a normal serum potassium level (3.9 mmol/L [normal = 3.5-5]). However, there was severe hypomagnesemia (0.39 mmol/L [normal = 0.65-1.25]) precipitating digoxin-induced dysrhythmia, which responded well to intravenous magnesium therapy.

This case reiterates that digoxin toxicity can occur in patients with normal digoxin and potassium levels, and in such patients, magnesium needs to be checked and treated to prevent potentially life-threatening dysrhythmias.