Pharm 100 - Lesson B.10
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- Nicotine is a naturally-occurring substance that is found in tobacco. Nicotine, caffeine and alcohol are the three most used psychoactive drugs in society. Nicotine has no therapeutic value other than insmoking cessation programs. It is extremely important, however, that tobacco use results in a largenumber of health problems and is responsible for approximately 100 deaths each day in Canada.
- Use of tobacco products increased from the 1940’s until the 1970’s as it was considered “cool” tosmoke. This era also saw an increase in the number of women smoking. Over the last two decades, the percent of the adult population who smoke steadily declined to where 27% of both males and females over the age of 15 smoked in 1995. This is a high figure if one considers the effects of smoking incausing cancer and its role in cardiovascular disease. The 27% of the male population who currentlysmoke has declined from a higher 61% in 1965. It is not nicotine which is responsible for the long-termeffects of smoking, but other compounds found in tobacco and tobacco smoke.
Pharmacology of Nicotine
- Nicotine stimulates nicotinic receptors in the central nervous system, including the cerebral cortex,producing increased psychomotor activity, cognitive function, attention and enhanced memory. In largedoses, it can cause agitation, tremors and seizures. The effects in the central nervous system aremediated, at least in part, by nicotinic receptor mediated release of dopamine and serotonin (another CNStransmitter).
- In the peripheral nervous system, nicotine stimulates the sympathetic ganglia and thus drives the sympathetic nervous system. This results in an increase in heart rate and blood pressure.
- Nicotine has powerful reinforcing properties and it is nicotine in tobacco products that isresponsible for the dependence.
- Nicotine exists in cigarette smoke in very small particles, and when inhaled, these droplets arerapidly absorbed. Approximately 20% of the nicotine in a cigarette is absorbed following “normalsmoking” and inhaling of the smoke. Nicotine is absorbed as well, from the gastrointestinal tract, oralmucosa and across the skin (transdermal) (nicotine is available as a gum and as patches). Nicotine is distributed throughout the body and rapidly penetrates to the brain. It readily crosses the placenta andmay have deleterious effects on the fetus.
- Nicotine is rapidly metabolized in the liver and the metabolites are excreted in the urine. The halflife of nicotine in the body is about two hours.
Medical Use of Nicotine
The only medical use of nicotine is in smoking cessation programs. Nicotine is administered in theform of a chewing gum or as transdermal patches. This approach is an attempt to maintain the bloodnicotine levels and satisfy the craving for a cigarette. The use of nicotine in a gum or patch allows the tapering off of the nicotine dose.
Effects of Short-Term Use
- In the non-smoker, a few puffs of a cigarette may result in dizziness, headache, nausea, vomitingand abdominal cramps. The smoke may trigger coughing or gagging. These symptoms disappear in the chronic user.
- With regular use, nicotine produces mild euphoria, enhanced arousal, increased ability to concentrate, a sense of relaxation, and of course, a reduction in the urge to smoke. Nicotine may cause asmall increase in heart rate and blood pressure. Nicotine may depress appetite.
Effects of Long-Term Use
Cigarette smoking is recognized as the major preventable cause of premature death in Canada. Tobacco smoke contains nicotine, carbon monoxide, and thousands of other compounds, some of whichare carcinogens. The cost to society is staggering: out of every 1000 Canadians aged 20 who smoke,500 will die from smoking-related diseases before the age of 70. In Canada, 21% of deaths from allcauses is attributable to cigarette smoking. The social and economic cost estimates range from $9.5 to$12.3 billion per year in Canada. A portion of this cost is offset by tobacco taxes, reduced health carecosts to the elderly, and reduced pension payments, as these people die a premature death.
Cardiovascular disease is caused by two components
- Cardiovascular disease is caused by two components in cigarette smoke – nicotine and carbonmonoxide.
- Carbon monoxide reduces the capacity of the red blood cells to carry oxygen. Both of thesecompounds increase the incidence of atherosclerosis (plaques in the vessel) and formation of thrombi(blood clots). There is a 5- to 19-fold increase in risk of death due to cardiac causes in the smoker. InCanada, 11,000 people per year will die of smoking-related cardiovascular disease; this is one-third ofdeaths due to all cardiac causes
Lung disease is also increased by smoking. There is a smoker’s syndrome, characterized bydifficulty in breathing, wheezing, chest pain, congested lung, and increased lung infections. There is anincreased risk of emphezema and other forms of chronic obstructive lung disease.
The cancer risk associated with smoking has now been defined beyond doubt. Anyone who claimsthat there is no cancer risk with smoking, is either a fool, an idiot, or both. Thirty percent of all cancersare estimated to be caused by cigarette smoke. Cigarette smoke is known to increase the risk of cancer ofthe lung, the oral cavity and throat, the bladder, and the uterus
- The effects of passive smoke is also associated with an increased risk of cardiovascular disease and cancer to the individual exposed to passive smoke (a non-smoker in the presence of smokers). It isestimated that 300 Canadians will die this year from lung cancer induced by passive smoke. The numberof deaths due to cardiovascular disease is even greater
- In children “passive smoke” increases the risk of bronchitis and pneumonia, asthma and suddeninfant death syndrome.
Tolerance and Dependence
- Biological tolerance does not appear to occur to any great extent. Most smokers will smoke to keep nicotine blood levels at a certain range (30 to 40 nanograms/millilitre). The number of cigarettes smokedeach day is the number needed to keep the nicotine at this level. It is noteworthy that the smoker is in astate of nicotine withdrawal upon awakening in the morning.
- Physical and psychological dependence both occur to nicotine. Withdrawal from smokinginvolves a number of symptoms. These are irritability, restlessness, anxiety, insomnia, fatigue, inabilityto concentrate, and an extreme urge to smoke. The latter two may persist for months. Cessation-ofsmoking programs usually involve counselling and pharmacological support.
Potential for Abuse
Nicotine is a powerful reinforcer and has a high degree of abuse liability. Individuals will beginsmoking because of peer pressure, or because it is the chic thing to do. Health Canada and the RoyalSociety of Canada both state that tobacco products meet all the requirements of addicting substances. Attempts at cessation of smoking often fails, the craving of nicotine is so great. Nicotine replacementprograms (gum or patches) with counselling and support is somewhat more successful than cessationwithout adjunctive therapy
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