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Lecture 6

Lecture 6 - Nicotine .docx

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Pharmacology and Therapeutics
PHAR 300
Edith Zorychta

Lecture 6- Nicotine Question: Tolerance to a centrally active drug ( acting on CNS) can result from: 1. decrease in R number 2. increase in R number 3. Decrease in transmitter synthesis 4. Increase in transmitter synthesis 5. All of the above Answer: 5  CNS has all sorts of techniques it can use to counteract the effect of drugs (adaptation, tolerance) Nicotine: - The nicotinic receptor is called nicotinic because it is nicotine that stimulates it - Nicotine is a natural ingredient of the tobacco plant - It is the active drug that people get addicted to in cigarettes Smoking: Drug delivery system which is very effective - You are inhaling drug into the lungs ( large surface area for absorption) and the contents of the lungs gets right into the blood stream and then into the heart and then due to the large cardiac output to the brain, directly to the brain - It takes about 7 seconds for the nicotine to get from the lungs to the brain - It is equivalent to intravenous administration - Delivery system to more than 4,000 drugs inside the cigarette ( dependent on solubility) - there are many relatives of nicotine in cigarette o similar alkaloids, some of which have a definite biological effect o They are not removed by filters o The filters only remove the large particles of tar Toxicity of cigarettes: - Deaths from cigarette is very large ( as seen in the pie chart) - 6 million people per year die from cigarette - 30% of cancer deaths are due to smoking o breast o prostate o lung o bladder o etc…. - There is a correlation between the inability to clear substances out of your lungs and the amount you smoke - The relative risk of developing lung cancer is linearly proportional to the # of cigarettes smoked but there is no safe limit o A carcinogen affects all cells - Bladder cancer is very common in smokers o There are many differet problems ( cardiovascular, lung disease, cancers and other problems) - Coronary heart disease: o 1/3 of deaths are due to smoking o Causes harm to the cilliary in the lungs o Increase in blood clotting o Hypertension o Carbon monoxide intake - Stroke: o Impaired blood flow to a region of the brain o Many people who get strokes are young, and they are usually impaired for the rest of their life - Vasoconstriction: o Impairing blood flow to the periphery o To skin, eyes, hair, gums (major consequences on appearance) o This all happens during the “actual smoking itself” - Bronchitis and emphysema: o 20% of smokers die from chronic lung diseases o Impairment in lungs o Bronchitis = lungs full of mucous - Cigarettes cause 50% of deaths - Smoking during pregnancy causes increased risk of spontaneous abortion o It also causes the lower birth weight of baby, which is linked to various other problems o Exposing babies to second-hand cigarette smoke also increases the risk of sudden infant death and many others. - Second hand smoke is harmful as well Pharmacokinetics of nicotine: - Nicotine is a weak base, thus its absorption depends on the pH o Weak acids/weak bases will be ionized/unionized depending on the environment o When nicotine is in a neutral environment, it will be unionized thus it will be lipid soluble o This means it can more readily cross lipid membranes and more readily absorbed - Question: cigarette companies add ingredients to make the tobacco more BASIC so that it can cross the membrane faster - The ½ life of nicotine is 2 hours o So if you sleep 8 hours you sleep 4 ½ lives and have no effects anymore - Different brands of cigarettes have different contents of nicotine, CO, etc. Some of them have quite different levels of nicotine. However, counter-intuitive to what most people may think, different nicotine level is not a significant factor for blood nicotine level of smokers. Different types of cigarettes with different levels of nicotine end up giving roughly the same plasma concentration of nicotine (people who smoke cigarette with much lower nicotine content achieve almost the same blood nicotine level as the control). o The smoker controls bioavailability of the drug (puffs, how long it is held in lungs, # smoked per day, per hour etc…) o So the fact that a cigarette with ‘less” nicotine is said to be “healthier” is false, because the smoker will change the way he smokes accordingly to receive the same blood [nicotine] o The smoker will just smoke ‘differently’ - Excellent GI absorption (poisoning) o Children may swallow cigarette and this lethal to ingestion - Distribution: o The distribution affects all the nicotinic receptor both (CNS and PNS) o The nicotine enters the brain and enters relatively quickly to the chemoreceptor trigger zone (no blood brain barrier  no glial cells) o If a child eats a cigarette, they can get a lethal dose of nicotine ( from a high nicotine cigarette or cigar) but what usually happens is that it triggers vomiting. They will vomit it out before digestion. The chemoreceptor trigger zone is a safety mechanism that when a poison is ingested, it will cause nausea in attempts to “help” the body - Metabolism: Cytochrome P450 o CYP2A6 break nicotine cotinine (biologically active) o There is a variation of CYP2A6 in the human population o Some have defective CYP2A6 alleles  This means that level of nicotine in your body will stay high for longer  Smoke fewer cigarettes to maintain a high level of nicoti
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