Urinary metabolite cotinine

The major human urinary metabolites of nicotine are cotinine, nicotine A -oxide, and fra s-3 -hydroxycotinine (113). CYP2A6 appears to be the major enzyme responsible for formation of an iminium ion that is the first step in the C-5 oxidation of nicotine to cotinine and also the subsequent... 

Miscellaneous compounds of pharmacological interest have been shown to inhibit aromatase in vitro, including the antimalarial drug mefloquine, [138], the oral hypoglycaemic agent, tolbutamide [139], and nicotine, its metabolite cotinine, and anabasine, all of which are found in tobacco [140]. These effects probably have little clinical relevance, although the latter three compounds may account for the reduced urinary [141] and plasma [142] oestrogen concentrations found in smokers [140],... 

Nicotine and its metabolites are quickly excreted in the urine. The half-life of nicotine in plasma is 1.6-2.8 h and that for cotinine is 8-29.3 h. Approximately 10-20% of the absorbed nicotine dose is excreted unchanged. Urinary excretion of nicotine is pH dependent, increasing in acid urine. 

---