Pharmacology
Summary
Varenicline is a medication used to assist individuals in smoking cessation. Cigarette smoking remains the number one cause of preventable disease and death in the United States, killing more than 480,000 Americans each year, and understanding its addictive nature involves exploring the role of nicotine on the brain. Nicotine tolerance develops due to repeated exposure to nicotine, which can lead to physical dependence and-- if nicotine is absent-- withdrawal symptoms. While nicotine replacement therapy (NRT) is successful for many people, varenicline is another pharmacological option for those who have failed multiple attempts with NRT.
Varenicline is a partial agonist at nicotinic receptors, which means it stimulates these receptors with less intensity than full agonists. It also blocks nicotine from binding to these receptors, which ultimately helps patients in curbing the addiction. Varenicline requires a gradual dose titration, where the dose increases over the first week of therapy, and since varenicline is primarily eliminated by renal glomerular filtration and active tubular secretion, it may need to be adjusted for patients with severe renal impairment. Smoking cessation may alter the pharmacokinetics or pharmacodynamics of certain drugs with narrow-therapeutic indexes or those associated with significant toxicity risks, like theophylline, warfarin and insulin, which may also necessitate a dosage adjustment for the drug. It's important to monitor patients attempting to quit smoking with varenicline if they experience serious adverse side effects, such as neuropsychiatric events (e.g. mood changes or suicidal ideation), seizures, varenicline-alcohol interactions, potential cardiovascular effects, and physiological changes due to smoking cessation. Other common side effects include constipation, flatulence, and vivid or unusual dreams.
Lesson Outline
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FAQs
Varenicline aids in smoking cessation by functioning as a partial agonist at nicotinic receptors. This means it both reduces cravings for nicotine and decreases the pleasurable effects of cigarettes and other tobacco products. This interplay aids in breaking the cycle of addiction.
Varenicline requires an upward dose titration when beginning the regimen. It starts with a dose of 0.5 mg once daily for 3 days, then moves to 0.5 mg twice daily for 4 days, and finally reaches a maintenance dosage of 1 mg twice daily. The total therapy course lasts for 12 weeks.
Common side effects of varenicline can include nausea, vomiting, constipation, and flatulence. Some patients using varenicline have also reported experiencing vivid, unusual, or strange dreams.
Varenicline has been associated with certain risks including neuropsychiatric side effects like mood changes and suicidal ideation. It has also been linked with new or worsening seizures, increased alcohol effects, and a potential increased risk of cardiovascular events. As a result, the use of varenicline should be approached with caution in patients with a history of seizures or cardiovascular disease, and users should also monitor their alcohol consumption.
Dosage adjustments may be necessary in the use of varenicline for those with severe or end-stage renal disease, as indicated by an estimated creatine clearance (CrCl) less than 30 mL/min. Smoking cessation, itself, might also lead to changes in the pharmacokinetics and dynamics of certain drugs due to alterations in CYP450 levels, which could require dosage adjustments or therapeutic drug monitoring.
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