Classification of digoxin concentrations in blood and tissues in cases under suspicion of poisoning

Abstract

The clarification of a suspicion of poisoning at all times poses a problem to the forensic toxicologist, when a narrow margin of therapeutic safety and a low dosage coincide as in cases of digoxin poisoning. Statistical methods may serve as an aid. The post mortem digoxin concentration in the tissues of heart, kidney, liver and in blood of 45 patients who had received therapeutic daily doses and of 13 cases of fatal poisoning are compared. After logarithmic transformation of the individual concentration values a two modal distribution is obtained. There is one concentration calculated with equal probability of being classified to "therapeutic or toxic", as well as the probability of observing the "critical" concentrations of 400 ng digoxin/g cardiac tissue, 500 ng/g kidney and 250 ng/g liver after therapeutic dosing. Using the discriminant analysis each of the cases clearly falls into one of the two collectives "therapeutic" and "toxic", when taken as a separate observation. Concentration data of fatal poisonings taken from the literature are as successfully classified as the analytical results of some exhumed bodies under suspicion but not poisoned. As expected the power of discrimination increases with the number of parameters. Because of the relatively slow body distribution of digoxin the blood taken from peripheral vessels is of most important evidence.