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Effect of smoking cessation: Physiological changes resulting from smoking cessation, with or without treatment with varenicline, may alter the pharmacokinetics or pharmacodynamics of some medicinal products, for which dosage adjustment may be necessary (examples include theophylline, warfarin and insulin) (see Warfarin under Interactions.)
At the end of treatment, discontinuation of varenicline was associated with an increase in irritability, urge to smoke, depression, and/or insomnia in up to 3% of patients.
There have been post-marketing reports of neuropsychiatric symptoms, some serious, including changes in behavior or thinking, anxiety, psychosis, mood swings, aggressive behavior, agitation, depressed mood, suicidal ideation and suicidal behavior, in patients attempting to quit smoking with varenicline (see Adverse Reactions).
A large randomized, double-blind, active and placebo-controlled study was conducted to compare the risk of serious neuropsychiatric events in patients with and without a history of psychiatric disorder treated for smoking cessation with varenicline, bupropion, nicotine replacement therapy patch (NRT) or placebo. The primary safety endpoint was a composite of neuropsychiatric adverse events that have been reported in post-marketing experience. The use of varenicline in patients with or without a history of psychiatric disorder was not associated with an increased risk of serious neuropsychiatric adverse events in the composite primary endpoint compared with placebo (see Pharmacology: Pharmacodynamics: Study in Subjects with and without a History of Psychiatric Disorder under Actions).
A causal relationship between serious neuropsychiatric events and varenicline has not been established. Physicians should observe patients attempting to quit smoking with or without varenicline for the occurrence of serious neuropsychiatric symptoms and should instruct patients to contact a healthcare professional if they experience such symptoms.
In clinical trials and post-marketing experience there have been reports of seizures in patients with or without a history of seizures, treated with varenicline. Varenicline should be used cautiously in patients with a history of seizures or other conditions that potentially lower the seizure threshold. Causal relationship between these reports and varenicline use has not been established.
There have been post-marketing reports of hypersensitivity reactions including angioedema in patients treated with varenicline. Clinical signs included swelling of the face, mouth (tongue, lips, and gums), neck (throat and larynx) and extremities. There were rare reports of life-threatening angioedema requiring urgent medical attention due to respiratory compromise. Patients experiencing these symptoms should discontinue treatment with varenicline and contact a healthcare provider immediately.
There have also been post-marketing reports of rare but severe cutaneous reactions, including Stevens-Johnson Syndrome and Erythema Multiforme in patients using varenicline. As these skin reactions can be life-threatening, patients should discontinue treatment at the first sign of rash or skin reaction and contact a health care provider immediately.
In a smoking cessation study in patients with stable cardiovascular (CV) disease and in a meta-analysis of 15 clinical trials, some CV events were reported more frequently in patients treated with varenicline compared to placebo. These events occurred primarily in patients with known CV disease. No causal relationship between these events and varenicline has been established. In a large smoking cessation trial that assessed CV safety in patients with and without a history of psychiatric disorder, major CV events (CV death, non-fatal MI, non-fatal stroke) were reported less frequently in patients treated with varenicline compared to placebo. In these studies, major CV events were infrequent overall and all-cause and CV mortality was lower in patients treated with varenicline compared to patients treated with placebo. Smoking is an independent and major risk factor for CV disease. Patients should be instructed to notify their healthcare providers of new or worsening cardiovascular symptoms and to seek immediate medical attention if they experience signs and symptoms of myocardial infarction or stroke (see Pharmacology: Pharmacodynamics: Study in Subjects with Cardiovascular Disease, Cardiac Assessment Study under Actions).
Effects on ability to drive and use machines: Patients should be advised to use caution driving or operating machinery until they know how quitting smoking and/or varenicline may affect them.
