The effects of intravenous calcium in patients with digoxin toxicity

Digoxin is an inhibitor of the sodium-potassium ATPase. In overdose, hyperkalemia is common. Although hyperkalemia is often treated with intravenous calcium, it is traditionally contraindicated in digoxin toxicity.

To analyze records from patients treated with intravenous calcium while digoxin-toxic.

We reviewed the charts of all adult patients diagnosed with digoxin toxicity in a large teaching hospital over 17.5 years. The main outcome measures were frequency of life-threatening dysrhythmia within 1 h of calcium administration, and mortality rate in patients who did vs. patients who did not receive intravenous calcium. We use multivariate logistic regression to ensure that no relationship was overlooked due to negative confounders (controlling for age, creatinine, systolic blood pressure, peak serum potassium, time of development of digoxin toxicity, and digoxin concentration).

We identified 161 patients diagnosed with digoxin toxicity, and were able to retrieve 159 records. Of these, 23 patients received calcium. No life-threatening dysrhythmias occurred within 1 h of calcium administration. Mortality was similar among those who did not receive calcium (27/136, 20%) compared to those who did (5/23, 22%). In the multivariate analysis, calcium was non-significantly associated with decreased odds of death (odds ratio 0.76; 95% confidence interval [CI] 0.24-2.5). Each 1 mEq/L rise in serum potassium concentration was associated with an increased mortality odds ratio of 1.5 (95% CI 1.0-2.3).

Among digoxin-intoxicated humans, intravenous calcium does not seem to cause malignant dysrhythmias or increase mortality. We found no support for the historical belief that calcium administration is contraindicated in digoxin-toxic patients.