Table 2.

Metabolism of nicotine by 2′- and 5′-hydroxylation

System	2′-Hydroxylation as percent of 5′-hydroxylation
P450 2A6	11*†
Human liver microsomes	5.7†‡
Smokers' urine	13§

^*Based on relative rates of formation of aminoketone and cotinine. 

^† Data from a single nicotine concentration (61.7 μM). Values may differ at lower nicotine concentrations. Rates are estimates because cotinine is a secondary product. 

^‡ Based on relative rates of formation of keto acid and cotinine.§ Percent keto acid plus hydroxy acid (of nicotine metabolites in smokers' urine) divided by products of 5′-hydroxylation (from ref. 9).