The kinetics of red blood cell electrolyte alterations following digoxin administration. A report of two pediatric cases.

Serial determinations of plasma and red blood cell (RBC) Na+, K+, and Mg++ concentrations were obtained in 2 children following digoxin administration. Treatment with digoxin was associated with a 50-70% increase in the RBC Na+ concentration, whereas the RBC K+ concentration decreased by 7-10%. RBC electrolyte changes paralleled plasma digoxin levels in the child who was digitalized slowly, whereas the maximum shift in RBC electrolyte concentration occurred 48 h after peak plasma digoxin concentrations were observed in the child who had received a single dose of digoxin. These results suggest that Na+/K+-ATPase inhibition may continue after clearance of digoxin from the plasma. The use of plasma digoxin concentration to diagnose toxicity may be limited in the special case of children who have received a single large dose of digoxin.