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Varenicline; Indications/Uses, Dosage, Side Effects, Drug Interaction, Pregnancy

Varenicline is a partial agonist of the nicotinic acetylcholine receptor (nAChR) subtype alpha4beta2. Nicotine stimulation of central alpha4beta2 nAChRs located at presynaptic terminals in the nucleus accumbens causes the release of the neurotransmitter dopamine, which may be associated with the experience of pleasure; nicotine addiction constitutes a physiologic dependence related to this dopaminergic reward system. As an AChR partial agonist, varenicline attenuates the craving and withdrawal symptoms that occur with abstinence from nicotine but is not habit-forming itself.

Varenicline is a prescription medication used to treat nicotine addiction. It both reduces cravings for and decreases the pleasurable effects of cigarettes and other tobacco products. Varenicline is a prescription medication used to treat smoking addiction. This medication is the first approved nicotinic receptor partial agonist. Specifically, varenicline is a partial agonist of the alpha4/beta2 subtype of the nicotinic acetylcholine receptor.

It is a high-affinity partial agonist for the α4β2 nicotinic acetylcholine receptor subtype (nACH) that leads to the release of dopamine in the nucleus accumbens when activated, and therefore, has the capacity to reduce the feelings of craving and withdrawal caused by smoking cessation. In this respect, it is similar to cytisine and different from the nicotinic antagonist bupropion and nicotine replacement therapies (NRTs) like nicotine patches and nicotine gum.

Mechanism of action of Varenicline

Varenicline is an alpha-4 beta-2 neuronal nicotinic acetylcholine receptor, partial agonist. The drug shows high selectiviyty for this receptor subclass, relative to other nicotinic receptors (>500-fold alpha-3 beta-4, >3500-fold alpha-7, >20,000-fold alpha-1 beta gamma delta) or non-nicotinic receptors and transporters (>2000-fold). The drug competitively inhibits the ability of nicotine to bind to and activate the alpha-4 beta-2 receptor. The drug exerts mild agonistic activity at this site, though at a level much lower than nicotine; it is presumed that this activation eases withdrawal symptoms.

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Varenicline is a selective alpha4beta2 nicotinic acetylcholine receptor, partial agonist. The drug binds with high affinity and selectivity to alpha4beta2 nicotinic acetylcholine receptors located in the brain and stimulates receptor-mediated activity, but at a substantially lower level than nicotine;1 6 this low-level receptor stimulation and subsequent moderate, sustained release of mesolimbic dopamine are thought to reduce craving and withdrawal symptoms associated with smoking cessation. Varenicline also blocks the ability of nicotine to activate alpha4beta2 receptors, preventing nicotine-induced stimulation of the mesolimbic dopaminergic system and thereby reducing the reinforcement and reward effects of cigarette smoking.

Indications of Varenicline

Varenicline is used as an adjunct in the cessation of cigarette smoking.
For use as an aid in smoking cessation.
Smoking Cessation.

Contra-Indications of Varenicline

Schizophrenia
Manic-Depression
Having Thoughts of Suicide
alcoholism
alcohol intoxication
depression
Heart attack
Acute Syndrome of the Heart
Angina
Transient Ischemic Attack
stroke
Peripheral Vascular Disease
severe renal impairment
seizures
Feel Like Throwing Up
Increased Cardiovascular Event Risk

Dosage of Varenicline

Strengths: 0.5 mg; 1 mg; 0.5 mg-1 mg

Smoking Cessation

Smoking Cessation.
Days 1 to 3: 0.5 mg orally once a day
Days 4 to 7: 0.5 mg orally twice a day
Days 8 to end of treatment: 1 mg orally twice a day

Side Effects of Varenicline

The most common

Abnormal dreams
bloated or full feeling
change in taste
difficulty having a bowel movement (stool)
dry mouth
excess air or gas in the stomach or intestines
the general feeling of discomfort or illness
stomach pain or cramping
diarrhea
a headache
dizziness
confusion
stomach pain;
back pain, joint or muscle pain.
problems with your vision (including color vision);
sudden chest pain or trouble breathing;
pain or swelling in one or both legs;
a migraine headache;
pale skin, feeling light-headed or short of breath, rapid heart rate, trouble concentrating; or

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More common

Abdominal or stomach pain, discomfort, or tenderness
chills or fever
difficulty with moving
a headache, severe and throbbing
joint or back pain
muscle aching or cramping
muscle pains or stiffness
chest pressure or squeezing pain in the chest
discomfort in arms, shoulders, neck or upper back
excessive sweating
feeling of heaviness, pain, warmth and/or swelling in a leg or in the pelvis
sudden tingling or coldness in an arm or leg
sudden slow or difficult speech
sudden drowsiness or need to sleep
fast breathing
sharp pain when taking a deep breath
fast or slow heartbeat
coughing up blood
rust colored urine
decreased amount of urine

Rare

Anxiety
change in vision
chest pain or tightness
confusion
a cough
Agitation
arm, back, or jaw pain
blurred vision
chest pain or discomfort
convulsions
extra heartbeats
fainting
hallucinations
a headache
irritability
lightheadedness
mood or mental changes
muscle pain or cramps
muscle spasm or jerking of all extremities
nervousness

Drug Interactions of Varenicline

Varenicline may interact with the following drugs, supplements & may change the efficacy of the drugs

alcohol
bupropion
H2-antagonists (e.g., cimetidine, famotidine, ranitidine)
nicotine replacement therapy
quinolone antibiotics (e.g., ciprofloxacin, levofloxacin, norfloxacin)
trimethoprim
insulin
theophylline
warfarin

Pregnancy Catagory of Varenicline

FDA Pregnancy Category C

Pregnancy

This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Lactation

It is not known if varenicline passes into breast milk. If you are a breastfeeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breastfeeding. The safety and effectiveness of this medication have not been established for children.

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