A Comparison of Plasma and Urinary Nicotine and Cotinine Levels in Smokers and Nonsmokers: Nicotine Excretion Pathways Are Possibly Differential According to the Dosage of Tobacco Smoke Uptake

Summary

Nicotine and cotinine levels in plasma (pnic, pcot) and urine (unic, ucot) sampled at a steady state were studied in 83 smokers and 90 nonsmokers.

Although there was considerable interindividual variability in measured levels for any given self-reported number of cigarettes smoked per day (CPD), some regularity was discovered among these four levels in relation to CPD.

Average pnic and pcot increased in proportion to CPD up to 15 CPD and more than 50 CPD, but from 20 to 40 CPD, a discrepancy involving more pcot and less pnic was discovered. Average unic rose more rapidly than average ucot up to 15 CPD, but at above 20 CPD, ucot increased more predominantly than unic. In nonsmokers, these four levels were, if detectable at all, extremely low, particularly as concerns cotinine.

The results indicate that the nicotine excretion mechanism may be differential according to the recent uptaken nicotine dosage. In most nonsmokers, the main pathway for nicotine excretion is the nicotine to nicotine route (NNR). The nicotine to cotinine route (NCR) may act as a backup. Light smokers may acquire the ability to convert a greater amount of nicotine to cotinine in proportion to CPD, with both pathways equally available.

Predominant production and excretion of cotinine is suggested for smokers who smoke more than 20 CPD, with the main route replaced by NCR. In extremely heavy smokers who smoke more than 50 CPD, it is suggested that the transaction limits of the nicotine to cotinine conversion system are exceeded and that both pathways are at maximum availability.

As concerns the indicator of ETS exposure for nonsmokers, all four levels are not always completely measurable. It is suggested that pnic is the most sensitive, but all four markers are equally necessary to estimate the low dosage of tobacco smoke uptake.