385 INTERPRETATION OF PUTATIVELY TOXIC DIGOXIN SERUM CONCENTRATIONS IN CHILDREN

Abstract

Between January 1981 and April 1984 serum concentrations of digoxin in excess of 5 ng/ml were recorded in 47 children (age range 2 days to 16 years). In 10 of them high concentrations were measured 9-48 hours after death and were significantly higher than antemortem levels in all cases (8.3 ± 2.4 vs 3.3 ± 1.5, P < 0.0001). In 15 cases (40.5% of the living patients) serum concentrations of ≥ 5 ng/ml reflected sampling errors in that drug concentrations were monitored too soon after administration. On subsequent drug discontinuation later serum determinations were not in the toxic range. None of these children exhibited clinical digoxin toxicity. In 9 cases the excessive concentrations could be associated with renal failure and prolonged T½ of digoxin. In only two of these children were there signs of digoxin toxicity. Six cases were caused by digoxin overdose (accidental ingestions, dispensing error, suicide attempt, and excessive dose for age). In 6 additional cases the presence of an endogenous digoxin like substance (EDLS) could be shown as a component of elevated drug concentration. One case could be attributed to digoxin-amiodarone interaction. Overall, in 10/37 living patients digoxin toxicity was diagnosed. These observations suggest that serum concentrations of digoxin in excess of 5 ng/ml do not uniformly predict toxicity. Sampling errors, postmortem determinations and circulating EDLS should be considered as possible alternative explanations.