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In stock Manufacturer PFIZER US PHARM 00069047103
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Uses

Smoking Cessation

Varenicline is used as an adjunct in the cessation of cigarette smoking. The US Public Health Service (USPHS) guideline for the treatment of tobacco use and dependence recommends varenicline as one of several first-line drugs that may reliably increase long-term smoking abstinence rates. For additional information on smoking cessation, consult the most current USPHS Clinical Practice Guideline on Treating Tobacco Use and Dependence available at http://www.ahrq.gov/professionals/clinicians-providers/guidelines-recommendations/index.html.

Safety and efficacy of varenicline as an adjunct for smoking cessation have been established in 6 placebo-controlled or active-comparator studies in 3659 patients (mean age 43 years; 79-96% white) who were chronic cigarette smokers (approximately 21 cigarettes daily for an average of 25 years). Patients were treated with varenicline in conjunction with weekly 10-minute counseling (including provision of an educational pamphlet). Abstinence was determined by patients' self-report and verified by weekly measurements of expiratory carbon monoxide. Treatment was initiated 1 week prior to the target smoking cessation date.

In 2 such studies in patients who received varenicline (flexible dosages of 0.5-2 mg daily or fixed dosages of 1 or 2 mg daily) or placebo for 12 weeks and then were followed for 40 weeks post-treatment, continuous abstinence rates of 40-51 or 12%, respectively, during weeks 9-12 of treatment and 19-23 or 4-8%, respectively, during weeks 9-52 were reported.

In 2 randomized, double-blind, multicenter studies in patients who received varenicline (1 mg twice daily), extended-release bupropion (150 mg twice daily), or placebo for 12 weeks and then were followed for 40 weeks posttreatment, continuous abstinence rates during weeks 9-12 of treatment were higher with varenicline (44%) than with bupropion (30%) or placebo (17-18%); abstinence rates during weeks 9-52 were 21-22% with varenicline, 14-16% with bupropion, and 8-10% with placebo.

In a randomized, double-blind, maintenance-of-abstinence study, patients with a history of chronic smoking who had successfully quit smoking by the end of 12 weeks of open-label varenicline therapy were randomized to receive either varenicline (1 mg twice daily) or placebo for an additional 12 weeks. The additional 12 weeks of varenicline therapy (in those who achieved cessation of smoking) resulted in higher continuous abstinence rates during weeks 13-24 and during 28 weeks of posttreatment follow-up compared with placebo. Reported rates of abstinence for varenicline versus placebo were 70 versus 50% during weeks 13-24, and 54 versus 39%, respectively, during 28 weeks of posttreatment. Some clinicians state that since only individuals who had quit smoking by the end of the first 12 weeks of the study were randomized to receive the drug for an additional 12 weeks, about 33% of the participants (for whom the drug does not appear to be effective) were eliminated from the second phase, and thus the relapse prevention results may have limitations.

In these studies, the urge to smoke was less severe in individuals receiving varenicline than in those receiving placebo.

An alternative method for setting a target smoking cessation date was evaluated in a double-blind, placebo-controlled study in 651 patients who selected a target cessation date between 8 and 35 days after initiating varenicline treatment. Patients were randomized in a 3:1 ratio to receive varenicline (1 mg twice daily) or placebo for 12 weeks and then were followed for 12 weeks posttreatment. Continuous abstinence rates of 54 or 19% during weeks 9-12 of treatment and 35 or 13% during weeks 9-24 were reported in patients receiving varenicline or placebo, respectively.

A gradual approach to smoking cessation was evaluated in a double-blind, placebo-controlled study in 1510 patients who were unwilling or unable to make an immediate quit attempt. Patients received varenicline (1 mg twice daily) or placebo while gradually reducing the number of cigarettes smoked (by at least 50% within the first 4 weeks, followed by an additional 50% in the next 4 weeks, and then further reducing until complete abstinence by 12 weeks); patients continued to receive their assigned treatment for another 12 weeks and were followed through 52 weeks. Continuous abstinence rates were substantially higher with varenicline therapy versus placebo (32 versus 7% during weeks 15-24, and 24 versus 6% during weeks 15-52).

The efficacy of retreatment with varenicline was evaluated in a randomized, double-blind study in patients who had previously attempted to quit smoking with varenicline therapy and either did not succeed or relapsed after treatment; patients included in the study had received a minimum of 2 weeks of varenicline therapy at least 3 months prior to study entry and had been smoking for at least 4 weeks. Patients were randomized to receive either varenicline (1 mg twice daily) or placebo for 12 weeks and were followed for an additional 40 weeks posttreatment. Treatment with varenicline resulted in higher continuous abstinence rates during weeks 9-12 (45 versus 12%) and during weeks 9-52 (20 versus 3%) compared with placebo.

Efficacy and safety of varenicline given in conjunction with other smoking cessation therapies (e.g., bupropion, nicotine replacement therapy) have not been established.

Patients with Cardiovascular Disease

Safety and efficacy of varenicline also have been evaluated in a randomized, double-blind, placebo-controlled study in 703 patients with stable, documented cardiovascular disease (other than hypertension) who smoked at least 10 cigarettes daily; patients receiving varenicline and placebo were comparable in baseline characteristics, including age (mean age 57 and 55.9 years, respectively), race (80.3 and 80.8% white, respectively), gender (75.2 and 82.2% male, respectively), and mean smoking history (40 and 39 years, and 22.1 and 22.9 cigarettes daily, respectively). Treatment was initiated 1 week prior to the target cessation date. Among patients who received varenicline (1 mg twice daily) or placebo for 12 weeks and then were followed for 40 weeks posttreatment, continuous abstinence rates of 47 or 14%, respectively, during weeks 9-12 of treatment and 20 or 7%, respectively, during weeks 9-52 were reported. These results were comparable to results of 2 previous studies that had similar protocols but were conducted in generally healthy patients.(See Cardiovascular Effects under Cautions: Warnings/Precautions.)

Patients with Chronic Obstructive Pulmonary Disease

Safety and efficacy of varenicline also have been evaluated in a randomized, double-blind, placebo-controlled study in 460 patients (mean age 57 years, 82-84% white, approximately 62% male, mean smoking history of approximately 40 years) with mild to moderate chronic obstructive pulmonary disease (postbronchodilator FEV1/FVC below 70% and FEV1 at least 50% of predicted normal value) who smoked at least 10 cigarettes daily. Treatment was initiated 1 week prior to the target cessation date. Among patients who received varenicline (1 mg twice daily) or placebo for 12 weeks and then were followed for 40 weeks posttreatment, continuous abstinence rates of 41 or 9%, respectively, during weeks 9-12 of treatment and 19 or 6%, respectively, during weeks 9-52 were reported. These results were comparable to results of 2 previous studies involving the general smoking population.

Patients with Major Depressive Disorder

Efficacy and safety of varenicline in patients with major depressive disorder were evaluated in a randomized, double-blind, placebo-controlled postmarketing study in 525 adults 18-75 years of age with stable (current or past) major depressive disorder without psychotic features who smoked at least 10 cigarettes daily. Patients were receiving a stable antidepressant regimen for at least 2 months and/or had a successfully treated major depressive episode within the past 2 years. Among patients who received varenicline (1 mg twice daily) or placebo for 12 weeks and then were followed for 40 weeks posttreatment, continuous abstinence rates of 36 or 16%, respectively, during weeks 9-12 of treatment and 20 or 10%, respectively, during weeks 9-52 were reported. No clinically important differences in the incidence of suicidal ideation or behavior were observed between patients receiving varenicline and those receiving placebo, and no overall worsening of depression or anxiety occurred in either treatment group; however, these findings cannot be extrapolated to patients with untreated or active depression or more complex psychiatric conditions since such patients were excluded from the study.(See Neuropsychiatric Symptoms and Suicidality under Cautions: Warnings/Precautions.)

Dosage and Administration

Administration

Varenicline is administered orally. The drug should be taken after eating and with a full glass of water.

Dosage

Dosage of varenicline tartrate is expressed in terms of varenicline.

Smoking Cessation

The recommended adult dosage of varenicline as an adjunct in smoking cessation is 0.5 mg once daily on days 1-3, 0.5 mg twice daily on days 4-7, and 1 mg twice daily from day 8 through the end of 12 weeks of treatment. Therapy should be initiated 1 week before the target smoking cessation date. Alternatively, patients may begin treatment with varenicline and quit smoking between days 8 and 35 of treatment. Titration of the dosage during the initial week of treatment has been shown to reduce the incidence of drug-related nausea. The dosage of varenicline may be reduced temporarily or permanently in patients who experience intolerable adverse effects. In patients who have successfully stopped smoking by the end of 12 weeks of treatment, an additional 12 weeks of varenicline therapy is recommended to increase the likelihood of long-term abstinence.

Patients who are motivated but were unable to quit smoking during prior varenicline therapy (for reasons other than intolerability due to adverse events) or who relapsed after varenicline therapy should be encouraged to make another attempt to quit smoking once factors responsible for such failure have been identified and addressed.

Gradual Quit Approach

In patients who are unwilling or unable to abruptly quit smoking, a gradual approach to smoking cessation should be considered. Varenicline therapy should be initiated while gradually reducing the number of cigarettes smoked (by 50% within the first 4 weeks, followed by an additional 50% in the next 4 weeks, and then further reducing until complete abstinence by 12 weeks); treatment with varenicline should be continued for an additional 12 weeks for a total duration of therapy of 24 weeks. Patients should be encouraged to quit smoking sooner if they feel ready.

Special Populations

No dosage adjustment is needed in patients with mild to moderate renal impairment. In patients with severe renal impairment (creatinine clearance less than 30 mL/minute), an initial dosage of 0.5 mg once daily is recommended; dosage may be titrated as needed to a maximum of 0.5 mg twice daily. A maximum dosage of 0.5 mg once daily, if tolerated, is recommended in patients with end-stage renal disease who are undergoing hemodialysis.

No dosage adjustment is needed in patients with hepatic impairment.

No dosage adjustment is needed in geriatric patients; however, because geriatric patients are more likely to have decreased renal function, dosage should be selected cautiously.(See Geriatric Use under Warnings/Precautions: Specific Populations, in Cautions.)

Cautions

Contraindications

Varenicline is contraindicated in patients with a known history of serious hypersensitivity reactions or skin reactions to the drug.

Warnings/Precautions

Neuropsychiatric Symptoms and Suicidality

Serious neuropsychiatric events, including changes in mood (e.g., depression, mania), psychosis, hallucinations, paranoia, delusions, homicidal ideation, hostility, agitation, aggression, anxiety, panic, and suicidality (e.g., suicidal ideation, attempted and completed suicides), have been reported during postmarketing experience in patients receiving varenicline or bupropion (another smoking cessation drug). Such events have occurred in patients with or without preexisting psychiatric conditions, and some patients experienced worsening of their psychiatric illness. While some of the cases may have been confounded by symptoms of nicotine withdrawal typically seen in individuals who have stopped smoking, these effects also were observed in patients who continued to smoke. In addition, some neuropsychiatric effects, including unusual and sometimes aggressive behavior directed toward oneself or others, may have been worsened by concomitant use of alcohol.(See Drug Interactions: Alcohol.)

After the initial safety signal was identified from postmarketing reports, additional analyses and studies were conducted to further evaluate the possible association between varenicline and adverse neuropsychiatric effects. Results of several meta-analyses and large observational studies did not show an increased risk of serious neuropsychiatric events with varenicline and generally found similar rates of adverse psychiatric events (including hospitalizations) between varenicline and placebo or other smoking cessation therapies (i.e., bupropion, nicotine replacement therapy). Limited safety data from postmarketing studies of varenicline in patients with schizophrenia or major depressive disorder also showed no evidence of an increased risk of neuropsychiatric effects or worsening of the underlying psychiatric condition with use of the drug in these populations. In one such study in patients with stable schizophrenia or schizoaffective disorder, suicidal behavior and/or ideation were reported in 11 or 9% of patients receiving varenicline or placebo, respectively. No new emergences of suicidal behavior or ideation occurred in either group during the first week following treatment discontinuance. In another study in patients with stable major depressive disorder, neuropsychiatric symptoms including anxiety, depressed mood disorders and disturbances, and suicidal ideation or behavior were reported at similar rates in patients receiving varenicline or placebo. Patients who received varenicline in this study were more likely than those who received placebo to report one of various events related to hostility and aggression (3 versus 1%); however, scores on psychiatric rating scales were similar between the groups and no overall worsening of depression occurred.

As a postmarketing requirement to further assess the neuropsychiatric safety of varenicline and bupropion, the manufacturers conducted a large, randomized, double-blind, placebo- and active-controlled study (EAGLES) in more than 8000 smokers with or without a history of psychiatric disorders. Patients were stratified into a nonpsychiatric or psychiatric cohort and randomized to receive varenicline (1 mg twice daily), extended-release bupropion (150 mg twice daily), transdermal nicotine (21 mg/day with taper), or placebo; treatment was continued for a total of 12 weeks and patients were followed for an additional 12 weeks posttreatment. In this study, use of varenicline or bupropion was not associated with an increased risk of clinically important psychiatric events (as assessed by a composite safety end point of anxiety, depression, feeling abnormal, hostility, agitation, aggression, delusions, hallucinations, homicidal ideation, mania, panic, paranoia, psychosis, suicidal ideation, and suicidal behavior or completed suicide) compared with nicotine replacement therapy or placebo. However, patients with a history of psychiatric disorders were more likely than those without such a disorder to experience a neuropsychiatric event. In the psychiatric cohort, clinically important neuropsychiatric events occurred in 12.2, 11.8, or 9.8% of patients receiving varenicline, bupropion, or nicotine, respectively, and these event rates were greater for each of the active treatments compared with placebo (9.5%). In the nonpsychiatric cohort, such events occurred in approximately 3% of patients across treatment groups. Serious neuropsychiatric events, including those requiring hospitalization, were reported in less than 1% of patients with or without a psychiatric history in all treatment groups; one completed suicide occurred in a placebo-treated patient in the nonpsychiatric cohort.

Based on findings from the EAGLES study indicating that the risk of serious neuropsychiatric effects with varenicline and bupropion is lower than previously thought, FDA has removed the associated boxed warning that was included in the approved labeling for these drugs. Results of the study also confirmed the benefits of these smoking cessation therapies, which were observed regardless of whether patients had a history of psychiatric illness. Although the risk remains, particularly in individuals with current or past psychiatric illnesses (e.g., depression, anxiety disorder, schizophrenia), patients generally do not experience serious consequences such as hospitalization and, therefore, the benefits of smoking cessation (e.g., reduction in the risk of developing pulmonary disease, cardiovascular disease, or certain types of cancer) continue to outweigh the risks of these drugs. Health benefits associated with smoking cessation are immediate and substantial.(See Uses: Smoking Cessation.)

Patients receiving varenicline should be monitored for neuropsychiatric symptoms or for worsening of preexisting psychiatric conditions. Patients who experience agitation, hostility, depressed mood, or changes in behavior or thinking that are not typical for the patient or who develop suicidal ideation or suicidal behavior should discontinue varenicline therapy and immediately contact a clinician. The subsequent course of action (discontinuance of therapy, dosage reduction, or continued treatment under close monitoring) should be determined by the severity of symptoms and patient response to the smoking cessation treatment. Although resolution of symptoms after varenicline discontinuance was reported in many postmarketing reports, manifestations persisted in some cases. Therefore, ongoing patient monitoring and supportive care should be provided until symptoms resolve.

Seizures

Seizures have been reported during clinical trials and postmarketing experience in patients receiving varenicline; in most cases, seizures occurred within the first month of therapy. Some patients had no history of seizures, while others had a history of remote or well-controlled seizure disorders.

In patients with a history of seizures or other factors that can lower the seizure threshold, the potential benefits of varenicline should be weighed against the risk of seizures. Varenicline should be discontinued immediately if a seizure occurs during therapy.(See Advice to Patients.)

Concomitant Use of Alcohol

Decreased tolerance to alcohol has been reported during postmarketing experience in patients receiving varenicline.(See Drug Interactions: Alcohol.) At least 48 such cases have been reported since initial FDA approval of the drug in 2006. In some cases, unusual and sometimes aggressive behavior resulting in harm to a person or property also was reported; patients often had no memory or impaired memory of these events. The amount of alcohol consumed in these cases was not excessive for the individuals involved and not considered to be a sufficient explanation for the observed effects.

Patients should be instructed to reduce the amount of alcohol they consume while receiving varenicline until they know whether their tolerance for alcohol is affected by the drug.

Accidental Injury

Traffic accidents, near-miss incidents in traffic, or other accidental injuries have been reported during postmarketing experience in patients receiving varenicline. In some cases, the patients reported somnolence, dizziness, loss of consciousness or difficulty concentrating that resulted in impairment, or concern about potential impairment, in their ability to drive or operate machinery. Patients should be advised to exercise caution when driving or operating machinery or engaging in other potentially hazardous activities until the effects of the drug on the individual are known.

Cardiovascular Effects

During a controlled clinical trial of varenicline in patients with stable cardiovascular disease who smoked, certain cardiovascular events were reported more frequently in patients receiving varenicline than in patients receiving placebo. All-cause and cardiovascular mortality at 52 weeks of nontreatment follow-up were lower in patients receiving varenicline than in patients receiving placebo. Serious, nonfatal treatment-emergent events (events that occurred during treatment or within 30 days of completion) included nonfatal myocardial infarction (MI) and nonfatal stroke. Events occurring during 30 or more days after completing treatment (up to 52 weeks) included nonfatal MI, need for coronary revascularization, hospitalization for angina pectoris, transient ischemic attack, new diagnosis of peripheral vascular disease, or hospital admission for a peripheral vascular disease procedure. FDA analysis of this trial revealed a possible increased risk of these adverse cardiovascular events in patients with cardiovascular disease who received varenicline.

Subsequently, FDA required the manufacturer of varenicline to conduct a meta-analysis of placebo-controlled studies to further assess the cardiovascular safety of varenicline. This analysis included 15 randomized, placebo-controlled trials of at least 12 weeks' duration that provided data on more than 7000 patients (including 4190 treated with varenicline); the varenicline smoking cessation trial in patients with stable cardiovascular disease was included in the meta-analysis. Major adverse cardiovascular events (MACE; a composite end point of cardiovascular death, nonfatal MI, and nonfatal stroke), involving events occurring up to 30 days after treatment, were reported more frequently in patients receiving varenicline than in those receiving placebo (hazard ratio 1.95, 95% confidence interval 0.79-4.82). The estimated increase in MACE was 6.3 events per 1000 patient-years of exposure. Overall, these events were uncommon in both groups of patients and occurred principally in patients with known cardiovascular disease. Because event rates were low, the power for determining statistically significant differences between varenicline and placebo also is low. Although these findings are not statistically significant, the results are consistent across different time frames, subgroups, and sensitivity analyses. This meta-analysis found lower rates of overall mortality and cardiovascular mortality in patients receiving varenicline compared with those receiving placebo; however, this finding also was not statistically significant.

Varenicline has not been studied in patients with unstable cardiovascular disease or in patients who experienced a cardiovascular event during the 2 months prior to screening.

Because smoking is an independent and major risk factor for cardiovascular disease, smoking cessation is of particular importance in this patient population. The risks of varenicline should be weighed against the benefits of its use in smokers with cardiovascular disease.(See Patients with Cardiovascular Disease under Uses: Smoking Cessation.) Patients should be advised to notify a healthcare provider if they experience new or worsening symptoms of cardiovascular disease.

Somnambulism

Cases of somnambulism, sometimes resulting in harm to self, others, or property, have been reported in patients receiving varenicline. If somnambulism occurs, patients should discontinue varenicline and notify their healthcare provider.

Sensitivity Reactions

Hypersensitivity reactions, including angioedema, have been reported during postmarketing experience in patients receiving varenicline. Manifestations included swelling of the face, mouth (tongue, lips, and gums), extremities, and neck (pharynx and larynx). Life-threatening angioedema requiring emergent medical attention because of respiratory compromise has infrequently been reported. Patients should be instructed to discontinue varenicline and immediately seek medical attention if such symptoms occur.

Dermatologic Effects

Serious dermatologic reactions, including Stevens-Johnson syndrome and erythema multiforme, have been reported during postmarketing experience in patients receiving varenicline. Such reactions can be life-threatening; patients should be instructed to discontinue varenicline and to immediately contact their healthcare provider at the first appearance of a rash with mucosal lesions or any signs of hypersensitivity.

Nausea

Nausea, which is dose-related and often transient (although may persist for several months), is the most common adverse effect associated with varenicline, occurring in about 30% of patients titrated to the maximum recommended dose of 1 mg twice daily in several clinical studies; while nausea usually was mild or moderate, discontinuance of the drug was required in about 3% of those receiving varenicline at a dosage of 1 mg twice daily. Initial titration of varenicline dosage (see Dosage and Administration: Dosage) reduces the incidence of nausea. Dosage reduction should be considered in patients experiencing intolerable nausea.

Specific Populations

Pregnancy

Available human data are insufficient to determine whether varenicline is associated with a risk of major congenital malformations or miscarriage when used during pregnancy. In animal reproductive studies, varenicline did not produce any major malformations; however, there was some evidence of maternal toxicity, developmental toxicity, and decreased fetal weight when pregnant rats and rabbits were administered varenicline during the period of organogenesis at maternal exposures 36-50 times the exposure at the maximum recommended human dose.

Smoking during pregnancy is associated with known risks to the mother, fetus, and newborn infant; however, it is not known whether smoking cessation with varenicline may reduce these risks.

Lactation

Varenicline is distributed into milk in animals. It is not known whether the drug is distributed into human milk or if the drug has any effects on the breast-fed infant or on milk production. The known benefits of breast-feeding should be considered along with the mother's clinical need for varenicline and any potential adverse effects of the drug or underlying maternal condition on the infant.

Pediatric Use

Safety and efficacy of varenicline have not been established in patients younger than 18 years of age and use of the drug in this age group is not recommended. In a limited number of pediatric patients 12-17 years of age, systemic exposure to varenicline, as assessed by area under the concentration-time curve (AUC) and renal clearance of the drug, in pediatric patients weighing more than 55 kg was comparable to that of an adult population over the dosage range of 0.5-2 mg daily. At a varenicline dosage of 0.5 mg twice daily, steady-state exposure was approximately 40% higher in adolescents 12-17 years of age weighing 55 kg or less when compared with that of an adult population.

Geriatric Use

The pharmacokinetic profile of varenicline in healthy male and female smokers (65-75 years of age) who received 1 mg of the drug once or twice daily for 7 consecutive days was similar to that of younger individuals in one study. No substantial differences in safety and efficacy were observed relative to younger adults in this study, and other reported clinical experience has not identified differences in responses between geriatric patients and younger patients; however, increased sensitivity cannot be ruled out.

Varenicline is substantially excreted by the kidneys. Because geriatric patients are more likely to have decreased renal function, dosage should be selected cautiously; it may be useful to monitor renal function in such patients.

Renal Impairment

Varenicline is substantially eliminated by renal glomerular filtration along with active tubular secretion. Varenicline pharmacokinetics were unchanged in individuals with mild renal impairment (estimated creatinine clearance ranging from greater than 50 mL/minute up to 80 mL/minute); in individuals with moderate renal impairment (estimated creatinine clearance 30-50 mL/minute), varenicline exposure increased 1.5-fold compared with individuals with normal renal function (estimated creatinine clearance above 80 mL/minute). Dosage reduction is not required in patients with mild to moderate renal impairment.

In individuals with severe renal impairment (estimated creatinine clearance less than 30 mL/minute), varenicline exposure was increased 2.1-fold. In individuals with end-stage renal disease undergoing a 3-hour session of hemodialysis 3 days each week, varenicline exposure was increased 2.7-fold following administration of varenicline 0.5 mg once daily for 12 days; however, peak plasma concentrations and AUC were similar to those of healthy individuals receiving 1 mg twice daily. Varenicline was efficiently removed by hemodialysis in individuals with end-stage renal disease. Dosage adjustment is necessary for patients with severe renal impairment and for patients with end-stage renal disease undergoing hemodialysis.(See Dosage and Administration: Special Populations.)

Common Adverse Effects

In placebo-controlled studies, adverse effects reported in more than 5% of patients receiving varenicline and with an incidence twice the rate observed in those receiving placebo were nausea, abnormal (vivid, unusual, or strange) dreams, constipation, flatulence, and vomiting.

Drug Interactions

Physiologic changes resulting from smoking cessation (with or without varenicline) may alter the pharmacokinetics or pharmacodynamics of some drugs (e.g., theophylline, warfarin, insulin); dosage adjustment may be required.

The manufacturer states that clinical experience in patients receiving varenicline with other drugs has not revealed evidence of clinically important interactions.

Drugs Affecting or Metabolized by Hepatic Microsomal Enzymes

Pharmacokinetic interactions unlikely with drugs metabolized by or affecting cytochrome P-450 (CYP) isoenzymes. In vitro studies indicate that varenicline does not inhibit CYP isoenzymes 1A2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1, or 3A4/5 in vitro. The drug also does not induce CYP isoenzymes 1A2 or 3A4.

Drugs Eliminated by Renal Secretion

Clinically important pharmacokinetic interaction (requiring dosage reduction of varenicline) unlikely.

Metformin

Pharmacokinetic interaction unlikely. Varenicline (1 mg twice daily) did not alter the steady-state pharmacokinetics of metformin (500 mg twice daily); metformin had no effect on varenicline steady-state pharmacokinetics.

Alcohol

Increased intoxicating effects of alcohol can occur in patients receiving varenicline.(See Concomitant Use of Alcohol under Cautions: Warnings/Precautions.) Patients should reduce the amount of alcohol they consume while receiving varenicline until they know how the drug affects their tolerance to alcohol.(See Advice to Patients.)

Bupropion

Pharmacokinetic interaction unlikely. Safety of combined use of bupropion and varenicline not established.

Cimetidine

Potential pharmacokinetic interaction (increased plasma concentration of varenicline as a result of a reduction in renal clearance). Concomitant use with inhibitors of organic cation transporter OCT2 (e.g., cimetidine) may not necessitate varenicline dosage adjustment; increased systemic exposure to varenicline is not expected to be clinically important.

Digoxin

Pharmacokinetic interaction unlikely.

Nicotine

Pharmacokinetic interaction unlikely. Increased incidence of adverse effects (nausea, headache, vomiting, dizziness, dyspepsia, fatigue) and increased rate of discontinuance of combination (varenicline and transdermal nicotine replacement) therapy compared with those receiving transdermal nicotine and placebo. Safety and efficacy of varenicline in combination with other smoking cessation therapies have not been studied.

Warfarin

Pharmacokinetic interaction unlikely. Warfarin pharmacokinetics may be affected by smoking cessation.

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