Nicotine Distribution

    Here we see the rate at which nicotine is distributed through the body after inhalation. On average, a smoker absorbs about 1 mg of nicotine per cigarette. The nicotine is absorbed rapidly across pulmonary epithelium, into the arterial circulation, traveling via the carotid arteries to the central nervous system. Nicotine readily penetrates the blood-brain barrier, resulting in transient exposure of the brain to high levels of nicotine. Nicotine has been estimated to reach the brain within 10–20 seconds of inhalation. Following systemic distribution, however, the levels of nicotine in the brain decline rapidly.

    This graph shows the arterial and venous concentrations of nicotine achieved during cigarette smoking. Within 1 minute after smoking a cigarette, arterial levels of nicotine are nearly seven times the corresponding venous levels. These rapid, high levels of nicotine in the central nervous system produce an almost immediate effect, thereby reinforcing the behavioral act of smoking, which further stimulates repeated administration.

    Nicotine Excretion

    The half-life of nicotine in the body is approximately 2 hours. This rapid metabolism of nicotine to inactive compounds underlies tobacco users’ need for frequent, repeated administration of nicotine. With regular tobacco use, significant nicotine levels accumulate during waking hours.

    The half-life of cotinine, a major metabolite of nicotine, is much longer … about 16 hours. For this reason, cotinine can be used as a more reliable measure of tobacco use and exposure to second-hand smoke.

    Nicotine and other metabolites are excreted in the urine. Urinary excretion is pH dependent; the excretion rate is increased in acidic urine. Nicotine accumulates in breast milk and can be detected in the blood and urine of infants of nursing smokers.