Relation between plasma and red-cell electrolyte concentrations and digoxin levels in children.

We determined alterations in plasma and red-cell electrolyte concentrations associated with digoxin administration in 11 children in heart failure, 24 nontoxic patients receiving maintenance digoxin and 11 children in whom digoxin toxicity developed. Twenty normal children served as controls. Digoxin therapy was associated with a mean (+/- S.E.M.) increase in red-cell sodium from a pretreatment level of 6.2 +/- 0.7 meq per liter to 11.9 +/- 1.2 meq per liter and a decrease in red-cell potassium from 105.4 +/- 1.4 to 99.5 +/- 1.9 meq per liter (P less than 0.001). The red-cell sodium levels of toxic patients exceeded those of nontoxic patients whereas the potassium concentrations were lower (P less than 0.001). Toxic patients manifested significantly higher ratios of red-cell sodium to red-cell potassium (0.213 +/- 0.003) than nontoxic patients (0.085 +/- 0.008; P less than 0.001). Changes in red-cell electrolytes are sensitive indicators of digoxin affects.