Absorption Fate And Excretion

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Nicotine is readily absorbed from the respiratory tract, buccal membranes, and skin. Severe poisoning has resulted from percutaneous absorption. Being a relatively strong base, its absorption from the stomach is limited. Intestinal absorption is far more efficient. Nicotine in chewing tobacco, because it is absorbed more slowly than inhaled nicotine, has a longer duration of effect. The average cigarette contains 6-11 mg nicotine and delivers about 1-3 mg nicotine systemically to the smoker; bioavailability can increase as much as threefold with intensity of puffing and technique of the smoker.

Nicotine is available in several dosage forms to help achieve abstinence from tobacco use. Efficacy results primarily from preventing a withdrawal or abstinence syndrome. Nicotine may be administered orally as a gum (nicotine polacrilex, nicorette), transdermal patch (nicoderm, habitrol, others), a nasal spray (nicotrol ns), and a vapor inhaler (nicotrol inhaler). The first two are used most widely, and the objective is to obtain a sustained plasma nicotine concentration lower than venous blood concentrations after smoking (arterial blood concentrations immediately following inhalation can be as much as tenfold higher than venous concentrations). The efficacy of these dosage forms in producing abstinence from smoking is enhanced when linked to counseling and motivational therapy (see Chapter 23).

Approximately 80-90% of nicotine is altered in the body, mainly in the liver but also in the kidney and lung; cotinine is the major metabolite. The profile of metabolites and the rate of metabolism appear to be similar in smokers and nonsmokers. The t122 of nicotine following inhalation or parenteral administration is ~2 hours. Nicotine and its metabolites are eliminated rapidly by the kidney. The rate of urinary excretion of nicotine diminishes when the urine is alkaline. Nicotine also is excreted in the milk of lactating women who smoke; the milk of heavy smokers may contain 0.5 mg2L.

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