1-Methyl-5-(3-pyridinyl)-2-pyrrolidinone
Quantitatively, the most important metabolite of nicotine in most mammalian species is cotinine. In humans, about 70 to 80% of nicotine is converted to cotinine. This transformation involves two steps. The first is mediated by a cytochrome P450 system (mainly CYP2A6 and CYP2B6) to produce nicotine iminium ion. The second step is catalyzed by aldehyde oxidase (AOX). A number of cotinine metabolites have also been structurally characterized. Indeed, it appears that most of the reported urinary metabolites of nicotine are derived from cotinine.