The use of plasma metanephrine to normetanephrine ratio to determine epinephrine poisoning.

BACKGROUND: Intravenous epinephrine (EPI) is used as a pharmacologic agent to acutely treat patients in cardiac arrest. Unfortunately, there have been several homicide cases where hospitalized patients died due to a purposeful overdose of epinephrine. We measured plasma epinephrine metabolites (metanephrine, MET, and normetanephrine, NMET) to determine if exogenous epinephrine can be distinguished from endogenous epinephrine concentrations in a controlled animal study. METHODS: Rabbits were subjected to three different protocols. In the physiologic stress group (n=8), rabbits were immobilized for 30 min in a restraining tube. In the sub-lethal dose (n=9), 0.01 mg/kg of epinephrine was injected into anesthetized rabbits. In the lethal dose group (n=8), 1.0 mg/kg of epinephrine was administered into anesthetized rabbits. Blood was collected at regular intervals for up to 480 min. The plasma metanephrine and normetanephrine concentrations were measured by liquid chromatography/mass spectrometry and the serum cortisol concentrations by immunoassay. RESULTS: Serum cortisol and plasma metanephrine and normetanephrine concentrations increased in the stressed animals during immobilization demonstrating the endogenous stress model. Following a sub-therapeutic epinephrine dose, plasma metanephrine increased while plasma normetanephrine decreased. The peak plasma metanephrine concentrations were similar to the concentrations observed in the stressed animals; however, the ratio of plasma metanephrine to normetanephrine was significantly different. In the lethal epinephrine dose, both the plasma metanephrine concentrations and ratio of metabolites were significantly greater than those observed in the endogenously stressed animals. CONCLUSIONS: The ratio of plasma metanephrine to normetanephrine is the best marker to determine the presence of exogenous therapeutic and lethal epinephrine administration. However, there were limitations to the study design that could alter these conclusions.