Lethal toxicity from equimolar infusions of cocaine and cocaine metabolites in conscious and anesthetized rats

We compared the lethal toxicity of cocaine with that of three of its metabolites to determine the contribution of these metabolites to the lethal potential from cocaine infusion. Equimolar quantities of cocaine, norcocaine, benzoylecgonine, and ecgonine methyl ester were infused in conscious rats to determine onset of convulsions and respiratory arrest. In addition, the convulsive and respiratory toxicity for cocaine and norcocaine were evaluated in anesthetized rats and their circulatory toxicity in anesthetized and ventilated rats. Norcocaine infusion resulted in earlier onset of convulsions and respiratory arrest in conscious rats than cocaine and earlier onset of circulatory arrest. Plasma concentrations of norcocaine and cocaine were not different at these times. Benzoylecgonine and ecgonine methyl ester were less potent convulsants and respiratory depressants than norcocaine and cocaine, with ecgonine methyl ester more respiratory depressant than benzoylecgonine. Pentobarbital anesthesia enhanced the respiratory depression and suppressed or delayed the onset of convulsions from norcocaine and cocaine infusion. Prolonged infusion of cocaine to circulatory arrest resulted in benzoylecgonine concentrations ~60%, and norcocaine concentrations ~5%, of the cocaine concentration, but no detectable ecgonine methyl ester formation. We conclude that although norcocaine, ecgonine methyl ester, and benzoylecgonine administered separately have lethal potential in massive dosages, death from cocaine overdose primarily results from the parent compound and not from metabolite formation.