NICOTINE PHARMACOLOGY and PRINCIPLES of ADDICTION. 3 rd of 3 Prep for Session 1

Transcription

1 NICOTINE PHARMACOLOGY and PRINCIPLES of ADDICTION 3 rd of 3 Prep for Session 1

2 CHEMISTRY of NICOTINE Pyridine ring N H N CH 3 Pyrrolidine ring Nicotiana tabacum Natural liquid alkaloid Colorless, volatile base pk a = 8.0

3 NICOTINE ABSORPTION Absorption is ph dependent In acidic media Ionized poorly absorbed across membranes In alkaline media Nonionized well absorbed across membranes At physiologic ph ( ), ~31% of nicotine is unionized and readily crosses cell membranes At physiologic ph, nicotine (a weak base) is readily absorbed.

4 NICOTINE ABSORPTION: BUCCAL (ORAL) MUCOSA The ph inside the mouth is 7.0. Acidic media (limited absorption) Cigarette smoke Alkaline media (significant absorption) Pipes, cigars, spit tobacco, oral nicotine products Beverages can alter ph, affect absorption.

5 NICOTINE ABSORPTION: SKIN and GASTROINTESTINAL TRACT Nicotine is readily absorbed through intact skin Nicotine, although well absorbed in the small intestine, most (~75%) is metabolized before reaching the systemic circulation So, would a pill form of nicotine be effective?

6 NICOTINE ABSORPTION: LUNG Nicotine is distilled from burning tobacco and carried in tar droplets. Nicotine is rapidly absorbed in the lungs. Lung ph = 7.4 Extensive capillary system in lung Approximately 1 mg of nicotine is absorbed from each cigarette.

7 NICOTINE DISTRIBUTION Nicotine reaches the brain within seconds Arterial Venous Henningfield et al., Drug Alcohol Depend 1993;33:23-29.

8 NICOTINE METABOLISM and EXCRETION N H 10 20% excreted N unchanged in urine CH % cotinine Metabolized and excreted in urine (and breast milk) ~ 10% other metabolites Half-life Nicotine t ½ = 2 hrs Cotinine t ½ = 16 hrs Adapted and reprinted with permission. Benowitz et al. J Pharmacol Exp Ther 1994;268:

9 NICOTINE PHARMACODYNAMICS Central nervous system Pleasure Arousal, enhanced vigilance Improved task performance Anxiety relief Other Appetite suppression Increased metabolic rate Skeletal muscle relaxation Cardiovascular system Heart rate Cardiac output Blood pressure Vasoconstriction Nicotine binds to receptors in the brain and other sites in the body and has predominantly stimulatory effects

10 NEUROCHEMICAL & RELATED EFFECTS N I C O T I N E Dopamine Norepinephrine Acetylcholine Glutamate Serotonin -Endorphin GABA Pleasure, appetite suppression Arousal, appetite suppression Arousal, cognitive enhancement Learning, memory enhancement Mood modulation, appetite suppression Reduction of anxiety and tension Reduction of anxiety and tension Benowitz. Nicotine & Tobacco Research 1999;1(suppl):S159 S163.

11 WHAT IS ADDICTION? Compulsive drug use, without medical purpose, in the face of negative consequences Alan I. Leshner, Ph.D. Former Director, National Institute on Drug Abuse National Institutes of Health

12 NICOTINE ADDICTION U.S. Surgeon General Report (1988) Cigarettes and other forms of tobacco are addicting Nicotine is the drug in tobacco that causes addiction The pharmacologic and behavioral processes that determine tobacco addiction are similar to those that determine addiction to drugs such as heroin and cocaine U.S. Department of Health and Human Services. Office on Smoking and Health. The Health Consequences of Smoking: Nicotine Addiction. A Report of the Surgeon General, 1988.

13 Nicotine addiction is a form of chronic brain disease resulting from an alteration in brain chemistry BIOLOGY of NICOTINE ADDICTION: ROLE of DOPAMINE Nicotine stimulates dopamine release Nicotine addiction is not just a bad habit. Pleasurable feelings Discontinuation leads to withdrawal symptoms. Repeat administration Tolerance develops

14 CHRONIC ADMINISTRATION of NICOTINE: EFFECTS on the BRAIN Human smokers have increased nicotine receptors in the prefrontal cortex. High Low Nonsmoker Smoker Image courtesy of George Washington University / Dr. David C. Perry Perry et al. (1999). J Pharmacol Exp Ther 289:

15 NICOTINE PHARMACODYNAMICS: WITHDRAWAL EFFECTS Irritability/frustration/anger Anxiety Difficulty concentrating Restlessness/impatience Depressed mood/depression Insomnia Impaired performance Increased appetite/weight gain Most symptoms manifest within the first 1 2 days, peak within the first week, and subside within 2 4 weeks. Cravings (can experience months to years after quitting) HANDOUT Hughes. (2007). Nicotine Tob Res 9:

16 NICOTINE ADDICTION: They Cycle Tobacco users maintain a minimum serum nicotine concentration in order to Prevent withdrawal symptoms Maintain pleasure/arousal Modulate mood Users self-titrate nicotine intake by Smoking/dipping more frequently Smoking more intensely Obstructing vents on low-nicotine brand cigarettes Benowitz. (2008). Clin Pharmacol Ther 83:

17 Assessing Nicotine Dependence Fagerström Test for Nicotine Dependence (6 items) Developed in 1978 (8 items); revised in 1991 (6 items) Most common research measure of nicotine dependence; sometimes used in clinical practice Responses coded such that higher scores indicate higher levels of dependence Scores range from 0 to 10; a score >5 indicates substantial dependence Question 1: How soon after you wake up do you smoke your first cigarette? (Within 5 min = 3 pts; 6-30 min = 2 pts, min = 1) Heatherton et al. British Journal of Addiction 1991;86:

18 CLOSE TO HOME 2000 John McPherson. Reprinted with permission of UNIVERSAL PRESS SYNDICATE. All rights reserved.

19 FACTORS CONTRIBUTING to TOBACCO USE Environment Tobacco advertising Conditioned stimuli Social interactions Tobacco Use Physiology Genetic predisposition Coexisting medical conditions Pharmacology Alleviation of withdrawal symptoms Weight control Pleasure

20 TOBACCO DEPENDENCE: A 2-PART PROBLEM Tobacco Dependence Physiological The addiction to nicotine Treatment Behavioral The habit of using tobacco Treatment Medications for cessation Behavior change program Treatment should address the physiological and the behavioral aspects of dependence.

21 NICOTINE PHARMACOLOGY and ADDICTION: SUMMARY Tobacco products are effective delivery systems for the drug nicotine. Nicotine is a highly addictive drug that induces a constellation of pharmacologic effects. Nicotine activates the dopamine reward pathway in the brain, which reinforces continued tobacco use. Tobacco users who are dependent on nicotine selfregulate tobacco intake to maintain pleasurable effects and prevent withdrawal.

22 NICOTINE PHARMACOLOGY and ADDICTION: SUMMARY (cont d) Nicotine dependence is a chronic disorder. Tobacco use is complex, involving the interplay of the following: Pharmacology of nicotine (pharmacokinetics and pharmacodynamics) Environmental factors Physiologic factors Treatment of tobacco use and dependence requires a multifaceted treatment approach.