For many people, cigarettes are the delivery method of choice for a very addictive drug. Cigarettes enable you get a dose of nicotine into your body quickly and maintain adequate blood levels as a result of its unique pharmacokinetic profile. Pharmacokinetics is the study of the introduction of a drug like nicotine into the body, its movement among different parts of the body, its metabolism and eventual elimination from the body. Knowledge of nicotine metabolism and disposition may help researchers develop drugs and behavioral techniques to fight nicotine addiction.
Nicotine Absorption
You can get nicotine into your body by smoking pipes, cigars and cigarettes, or by using snuff or chewing tobacco. Newer dosage forms include nicotine gums, patches, lozenges, inhalers, sprays and tablets. When you smoke, 80 percent to 90 percent of the nicotine you inhale quickly reaches your bloodstream. Nicotine from dipping snuff and chewing tobacco enters the blood more slowly through tissues in your mouth. Nicotine products designed to help you stop smoking are intended to release nicotine into your system gradually. Your liver metabolizes most of the nicotine you swallow from snuff, chewing tobacco or nicotine gum before it reaches your general circulatory system.
Distribution and Metabolism
Once nicotine enters your blood, it converts into a chemical form that dissolves easily in body fluids and can travel freely throughout the body. Only 5 percent of the nicotine you ingest attaches itself to proteins. Nicotine is able to cross the blood-brain barrier and the placenta in pregnant women.
The half-life of nicotine from smoking is about two hours. Once you stop smoking, in two hours half the nicotine in your body after the last puff is eliminated. In two more hours, 75 percent of the original amount of nicotine is gone. If you smoke several cigarettes daily, you may be taking in nicotine faster than you are eliminating it. When this happens, nicotine blood levels gradually rise between cigarettes.
Nicotine Metabolites
Most of the nicotine in your blood is metabolized by the liver in to cotinine -- a compound found naturally in tobacco. Cotinine has psycho-pharmacological properties itself. Cotinine is eliminated slowly in the urine. Its half-life is 20 hours. Other nicotine and cotinine metabolites are more rapidly excreted in the urine. Some nicotine is eliminated in your feces and sweat.
Racial Differences
The rate of elimination or clearance of nicotine from the body can vary with the race of the smoker. A 1998 study published in "The Journal of the American Medical Association" found that black smokers absorbed 30 percent more nicotine per cigarette than white smokers. In addition, the elimination rate of nicotine and cotinine was lower in blacks than in whites.
Another study published in "The Journal of the National Cancer Institute" in 2002 found racial and ethnic differences in nicotine metabolism. This study measured nicotine absorption from cigarettes and nicotine metabolism in Chinese-Americans, Latinos, and whites. The researchers found that Chinese Americans absorbed less nicotine per cigarette than either whites or Latinos. In addition, the researchers found that the nicotine half-life of Chinese-Americans was longer: nicotine was cleared at a slower rate than in whites or Latinos.
References
- "The Journal of the National Cancer Institute"; Slower Metabolism and Reduced Intake of Nicotine From Cigarette Smoking in Chinese-Americans; Neal Benowitz, et al.; January 2002
- "The Journal of the American Medical Association"; Nicotine Metabolism and Intake in Black and White Smokers; Eliseo J. Pérez-Stable, et al.; July 1998
- "Pharmacological Reviews"; Metabolism and Disposition Kinetics of Nicotine; Janne Hukkanen, et al.; March 2005
- MedlinePlus: Nicotine Addiction and Withdrawal
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