Ethnic differences in nicotine metabolism have been hypothesized to contribute to differences in health effects and/or susceptibility to addiction in blacks versus whites (Henningfield et al. 1990). The intriguing observation has been made that cotinine levels per cigarette smoked were significantly higher in blacks versus whites (Wagenknecht et al. 1990). In contrast, plasma levels of thiocyanate, a marker of exposure to cigarette smoke in general, were similar. There is also evidence that blacks have higher rates of lung cancer for any given level of cigarette smoking compared with whites (Satariona and Swanson 1988). Ethnic differences in the metabolism of nicotine or cotinine could help explain these observations.
To examine this issue, dual-labeled nicotine and cotinine infusions were administered to 40 black and 39 white smokers matched for age, gender, and self-reported cigarette consumption (Benowitz et al. 1995a). The clearance of nicotine and percentage of nicotine conversion to cotinine were similar for blacks and whites. However, the clearance of cotinine was significantly slower (0.56 versus 0.69 mL/min/kg) and the half-life of cotinine slightly longer (1,064 versus 950 min) in blacks versus whites. These data clarify at least in part the observation of higher cotinine levels when normalized for cigarette consumption in blacks. The implications of differences in cotinine metabolism regarding susceptibility to nicotine addiction or health consequences of smoking are still unclear.
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