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Once absorbed, nicotine induces a variety of central nervous system, cardiovascular, and metabolic effects
Nicotine stimulates the release of several neurotransmitters, inducing a range of pharmacologic effects such as...
•Cognitive enhancement--> acetylcholine
•Appetite suppression--> dopamine, norepinephrine, serotonin
•Memory enhancement--> glutamate
•Mood modulation--> serotonin
•Reduction of anxiety/tension--> B-endorphin and GABA
what seems to be most responsible for the major addictive properties of nicotine
Nicotine from tobacco directly stimulates
the acetylcholine receptors on dopamine-containing neurons, which are involved in the reinforcing centers of the brain, as a part of the mesolimbic system
The stimulation of these acetylcholine receptors from nicotine is responsible for...
the overflow of dopamine in the reward centers of the brain, resulting in extracellular dopamine within the nucleus accumbens and an increased firing of dopaminergic neurons
•Many subtypes of acetylcholine receptors are associated with nicotine addiction like...
-Acetylcholine-receptor subtypes, such as α4ß2, are ligand-gated ion channels found on the dopaminergic neurons and on the γ-aminobutyric acid (GABA)-containing cells-->These receptors are thought to play a principal role in the mediation of nicotine addiction
Unlike acetylcholine, which is degraded quickly by acetylcholinesterase, nicotine
remains active at the α4ß2 receptor sites for a prolonged period of time
While prolonged stimulation by most entities usually causes receptor down-regulation, nicotine stimulation at the acetylcholine receptors...
causes receptor up-regulation-->This up-regulation desensitizes acetylcholine receptors, resulting in physical dependence, tolerance, and withdrawal symptoms, thereby adding to the propensity for nicotine addiction
a network of nervous tissue that elicits feelings of pleasure in response to certain stimuli, is central to drug-induced reward
The dopamine reward pathway
key structures of the dopamine reward pathway include...
-the ventral tegmental area (VTA)
-prefrontal cortex (the area of the brain responsible for thinking and judgement)
The neurons of the VTA contain
the neurotransmitter dopamine, which is released in the nucleus accumbens and in the prefrontal cortex
Immediately after inhalation, a bolus of nicotine enters the brain, stimulating...
the release of dopamine-->which induces nearly immediate feelings of pleasure, along with relief of the symptoms of nicotine withdrawal (This rapid dose response reinforces repeated administration of the drug and perpetuates the smoking behavior)
Chronic administration of nicotine has been shown to result in an increased number of nicotine receptors in specific regions of the brain, which is believed to represent...
upregulation in response to nicotine-mediated desensitization of the receptors and may play a role in nicotine tolerance and dependence
chronic administration of nicotine also leads to...
tolerance of the behavioral and cardiovascular effects of nicotine during the course of the day
resensitization of receptors
however, tobacco users regain sensitivity to the effects of nicotine after overnight abstinence from nicotine
Late in the day, each individual cigarette produces only limited pleasure or arousal; instead...
smoking primarily alleviates nicotine withdrawal symptoms
anger, anxiety, depression, difficulty concentrating, impatience, insomnia, and restlessness
improves cessation rates by reducing the physical withdrawal symptoms associated with tobacco cessation while the patient focuses on modifying his or her behavior and coping with the psychological aspects of quitting
Nicotine Replacement Therapy (NRT)
because the onset of action for NRT is not as rapid as that of nicotine obtained through smoking, patients...
become less accustomed to the nearly immediate, reinforcing effects of inhaled nicotine
reaches its peak concentration most rapidly
The nicotine nasal spray
have similar concentration curves
The nicotine gum, lozenge, and oral inhaler
has the slowest onset, but offers more consistent blood levels of nicotine for a sustained period
the nicotine transdermal patch
an atypical antidepressant medication hypothesized to promote smoking cessation by blocking the reuptake of dopamine and norepinephrine in the central nervous system and possibly by acting as a nicotine receptor antagonist
Sustained-release (SR) bupropion
These neurochemical effects are believed to modulate the dopamine reward pathway and reduce cravings for nicotine and symptoms of withdrawal
Treatment with SR bupropion should be initiated...
while the patient is still smoking, because approximately 1 week of treatment is necessary to achieve steady-state blood levels; Patients should set a target quit date that falls within the first 2 weeks of treatment, generally in the second week; Therapy should be continued for 7 to 12 weeks after the quit date
The most common adverse effects associated with this include insomnia and dry mouth; these usually lessen with continued use
Seizures are a dose related toxicity associated
because of the side effects of Sustained-Release Bupropion...
bupropion is contraindicated in patients with underlying seizure disorders and those receiving concurrent therapy with other forms of bupropion
Bupropion is contraindicated
-bupropion is contraindicated in patients with underlying seizure disorders and those receiving concurrent therapy with other forms of bupropion
-also contraindicated in patients with anorexia or bulimia nervosa
-patients undergoing abrupt discontinuation of alcohol or sedatives (including benzodiazepines)
-patients currently taking monoamine oxidase inhibitors, owing to the increased potential for seizures in this population
may be the drug of choice for patients who prefer to take oral medications (an alternative oral option to varenicline)
Because these tablets are easy to dose (twice daily oral dosing), this agent may be preferable for patients with regimen compliance concerns (e.g. those unable to consistently use short-acting NRT formulations that require multiple daily doses)
might be beneficial for use in patients with coexisting depression or in individuals with a history of depressive symptoms during a previous quit attempt
has been found to reduce post-cessation weight gain during treatment, and this might be of short-term benefit in selected patients with concerns about weight gain after quitting
High prevalence of insomnia and several contraindications and precautions that preclude use in some patients
a cytisine analog, is a partial agonist that binds with high affinity and selectivity at the α4ß2 neuronal nicotinic acetylcholine receptors
The efficacy of varenicline in smoking cessation is believed to be the result of...
sustained, low-level agonist activity at the receptor site combined with competitive inhibition of nicotine binding
The partial agonist activity induces modest receptor stimulation, leading to increased dopamine levels, which attenuates the symptoms of nicotine withdrawal
In addition, by blocking the ability of nicotine to activate α4ß2 nicotinic acetylcholine receptors, this inhibits the surges of dopamine release that are believed to be responsible for the reinforcement and reward associated with smoking
Treatment with varenicline should be initiated...
1 week before the patient stops smoking-->This dosing regimen allows for gradual titration of the dose to minimize treatment related nausea and insomnia
specifically binds to the α4ß2 nicotinic acetylcholine receptors acting as a partial agonist while also blocking the binding of nicotine
generally well tolerated however common side effects include nausea, sleep disturbance (insomnia, abnormal dreams), constipation, flatulence, and vomiting
first-line agent for the treatment of tobacco use and dependence
It offers a convenient oral dosing regimen and a novel mechanism of action that might be particularly appealing for patients who have failed quit attempts with other first line agents (e.g. NRT or sustained release bupropion)
Although not FDA approved specifically for smoking cessation, the prescription medications, these are recommended as second line agents
Lack of an FDA approved indication for smoking cessation and less desirable side-effect profiles currently prohibit these agents from achieving first-line classification
clonidine and nortriptyline
timing of second-line therapies
All patients who initiate pharmacotherapy should have initial follow-up (office visit or telephone call) within one to two weeks to assess for positive responses, side effects, and opportunities to optimize treatment with first-line therapies, and to provide reinforcement for smoking cessation when needed
Further follow-up to assess for new side effects, smoking cessation, or relapse, should be scheduled at three months and one year, and more frequently if necessary
If a patient does not stop smoking after two to four weeks of medication, one or more of the following may be occurring...
-Incorrect use of medications
-Intolerance of side effects
-Failure of the drug to reduce nicotine withdrawal symptoms, despite correct use of the medication
incorrect use of medications
The patient may be using the drug incorrectly (e.g., chewing nicotine gum too rapidly or not using gum or lozenge frequently enough). We suggest providing further precise education about how to use the drug(s). For example, assure that the patient understands how to titrate the short-acting nicotine replacement therapy (NRT) they have chosen to use (e.g., nicotine gum or nicotine lozenge) to prevent as well as relieve withdrawal symptoms
Intolerance of side effects
Before stopping the medication due to a non-serious side effect, we suggest lowering the dose. All three first-line medications can be effective at lower doses. For example, unpleasant dreams or insomnia can be ameliorated by taking a nicotine patch off at bedtime or by cutting out the evening dose of varenicline. If dose reduction is not feasible or successful, an alternate first-line agent should be tried
Failure of the drug to reduce nicotine withdrawal symptoms, despite correct use of the medication
If the patient is not already taking adjunctive short-acting NRT, we suggest adding it, with precise instructions on its effective use
Smokers who are already using a first-line oral pharmacotherapy along with appropriate use of short-acting NRT and still experience severe withdrawal symptoms should have the first-line medication dose increased if the dose is not yet maximized.
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