The most common complications of cocaine ingestion are on the cardiovascular and central nervous systems and produce chest pain and generalized seizures. In humans, decreased levels of butyrylcholinesterase (BChE) (EC 3.1.1.8) have been associated with sustained effects of cocaine and life-threatening complications. Administration of purified human BChE has previously been demonstrated to protect against cocaine-associated cardiovascular toxicity in rats. A shift in the metabolism of cocaine as well as enhanced metabolism may be the underlying mechanism of the enzyme. Therefore, levels of the parent drug and four metabolites were determined in rat plasma after i.p. administration of a lethal cocaine dose, followed by i.v. administration of BChE. Plasma and brain concentrations of cocaine were lowered by 80% after BChE administration. Furthermore, the metabolic profile of cocaine in the plasma was altered. The concentration of ecgonine methylester was doubled although the concentration of ecgonine, a secondary metabolite of cocaine, was reduced. The level of benzoylecgonine was reduced by one-half while norcocaine was absent. Cocaine-associated effects upon the central nervous system were also shown to be reduced by administration of BChE to conscious rats. Furthermore, our studies in the cat have also shown that purified BChE shifts the metabolic profile of cocaine (1 mg/kg) to the pharmacologically inactive products ecgonine methylester and ecgonine. Pretreatment with BChE (0.27, 1.0, and 10.0 mg/kg) ameliorated the hypertensive effects of cocaine (1 mg/kg) by reducing the duration and the extent of BP elevation by 66%. Administration of the enzyme, 1 min after cessation of cocaine infusion, resulted in an immediate attenuation in the cocaine-induced broadening of the QRS complex. These results suggest that BChE could be an effective and rapid therapy for the treatment of life-threatening cocaine-induced cardiovascular effects in human while clearing the total body burden of cocaine.