Bupropion

Introduction Overview

Generic Name

bupropion

Brand Name

Wellbutrin, Wellbutrin SR, Wellbutrin XL, Zyban, Aplenzin, Budeprion XL, Forfivo XL

Dosage Form

Immediate-release tablets, Sustained-release tablets, Extended-release tablets

Drug Class

Miscellaneous antidepressants and smoking cessation agents

Pharmacokinetics

Absorption

Bupropion is well absorbed orally with peak plasma concentrations reached within 2 to 3 hours for immediate-release formulations. Sustained-release tablets achieve peak concentration around 3 hours, while extended-release tablets peak around 5 hours post dosing. Absorption is not significantly affected by food, but taking bupropion with food may improve gastrointestinal tolerability. The absolute bioavailability is limited due to extensive first-pass metabolism. Dose-dependent increases in plasma concentrations have been observed, with saturation of metabolism at higher doses impacting pharmacokinetics.

Distribution

Following absorption, bupropion is widely distributed throughout the body. It is approximately 84% protein bound, primarily to albumin. The apparent volume of distribution ranges from 17 to 60 L/kg, indicating extensive tissue penetration. Bupropion and its active metabolites, particularly hydroxybupropion, distribute into the central nervous system to exert pharmacologic effects. The modest protein binding and large volume of distribution facilitate distribution into peripheral tissues and the brain.

Metabolism

Bupropion undergoes extensive hepatic metabolism primarily by the cytochrome P450 enzyme CYP2B6 to three active metabolites: hydroxybupropion, threohydrobupropion, and erythrohydrobupropion. These metabolites contribute significantly to the drug’s clinical effects, possessing antidepressant and smoking cessation properties. The metabolism involves hydroxylation, reduction, and glucuronidation processes. Genetic polymorphisms and drug interactions affecting CYP2B6 can significantly alter bupropion metabolism and exposure.

Elimination

The elimination half-life of bupropion is approximately 21 hours, whereas its active metabolites have longer half-lives ranging from 20 to 37 hours, supporting once or twice-daily dosing regimens. Bupropion and its metabolites are primarily eliminated renally as metabolites, with less than 1% of the unchanged drug excreted in urine. Renal impairment may necessitate monitoring but typically does not require dosage adjustment. Hepatic impairment can reduce metabolism, potentially increasing bupropion exposure, and warrants caution.

Dosage Forms

Adults

Bupropion is available as immediate-release tablets (75 mg, 100 mg), sustained-release tablets (SR) (100 mg, 150 mg, 200 mg), and extended-release tablets (XL) (150 mg, 300 mg). Dosages vary depending on the indication: for major depressive disorder (MDD), immediate-release is started at 100 mg twice daily increasing to 100 mg three times daily (max 450 mg/day); SR tablets begin at 150 mg once daily increasing to 150 mg twice daily (max 400 mg/day); XL tablets start at 150 mg once daily increasing to 300 mg once daily (max 450 mg/day). For seasonal affective disorder (SAD), XL formulations are typically dosed 150-300 mg once daily during autumn and winter months. For smoking cessation, SR tablets 150 mg once daily for 3 days, then 150 mg twice daily for 7-12 weeks; maximum dose 300 mg/day.

Adolescents

Bupropion’s safety and efficacy in pediatric populations, including adolescents, have not been adequately established. It is generally not recommended for use in children and adolescents due to increased risk of adverse effects, including seizures and suicidal ideation. If considered, careful risk-benefit analysis and close psychiatric monitoring are essential.

Special Populations

In patients with renal impairment, no dosage adjustment is generally necessary, but clinical monitoring is advised. Hepatic impairment can cause increased plasma levels due to reduced metabolism; dose adjustments or cautious use is recommended. Elderly patients may have increased sensitivity; treatment should start at low doses with careful titration. Bupropion is contraindicated in patients with seizure disorders or eating disorders such as anorexia nervosa or bulimia due to elevated seizure risk. It is not recommended during pregnancy unless benefits outweigh risks, and caution is advised during breastfeeding as the drug passes into breast milk.

Mechanism Of Action

Bupropion primarily acts as a norepinephrine-dopamine reuptake inhibitor (NDRI). It selectively inhibits the reuptake of norepinephrine and dopamine neurotransmitters in the brain by blocking their transporters, resulting in increased synaptic concentrations of these catecholamines. This elevated availability enhances neurotransmission, improving mood and reducing nicotine cravings. Unlike selective serotonin reuptake inhibitors (SSRIs), bupropion exerts minimal effect on serotonin systems, distinguishing its pharmacologic profile.

At the molecular level, bupropion binds to dopamine transporter (DAT) and norepinephrine transporter (NET) proteins, inhibiting reuptake and promoting increased extracellular neurotransmitter levels in mesolimbic and mesocortical pathways. This action contributes to its antidepressant effects and efficacy in smoking cessation by modulating reward and mood circuits. Bupropion's active metabolites, such as hydroxybupropion, also contribute to these effects by maintaining pharmacodynamic activity with longer half-lives.

Additionally, bupropion acts as a non-competitive antagonist of nicotinic acetylcholine receptors, which further supports smoking cessation by reducing the reinforcing effects of nicotine. This nicotinic receptor antagonism contributes to decreased dopamine release triggered by nicotine and helps mitigate withdrawal symptoms.

Clinically, bupropion improves depressive symptoms by enhancing catecholaminergic activity, whereas its dopaminergic modulation alleviates anhedonia and fatigue. It also benefits patients with seasonal affective disorder, possibly by countering reduced dopamine and norepinephrine function during low-light seasons. Its unique mechanism avoids common SSRI adverse effects like sexual dysfunction and weight gain, making it a preferred option in some patients. Research continues to explore its neurochemical interactions and potential benefits in other neuropsychiatric conditions.

Pharmacological Actions

Inhibition of norepinephrine reuptake increasing synaptic norepinephrine levels
Inhibition of dopamine reuptake enhancing dopaminergic neurotransmission
Non-competitive antagonism of nicotinic acetylcholine receptors reducing nicotine reinforcement
Active metabolites contribute to sustained pharmacologic effects
Enhancement of mood-regulating monoaminergic pathways
Reduction of nicotine cravings and withdrawal symptoms
Minimal serotonergic activity minimizing typical SSRI side effects
Promotion of weight loss or weight neutrality in contrast to other antidepressants
Stimulation of reward pathways aiding smoking cessation
Improvement in energy, concentration, and motivation in depressed patients
Modulation of neurotransmitters involved in seasonal affective disorder
Potential mild stimulant effects increasing psychomotor activity
No direct effect on GABAergic or glutamatergic systems

Therapeutic Clinical Uses

Treatment of major depressive disorder (MDD) in adults
Management of seasonal affective disorder (SAD) with extended-release formulations
Assistance with smoking cessation via reduction of nicotine cravings and withdrawal symptoms
Adjunctive treatment for weight management in combination with naltrexone (as in Contrave)
Improvement of depressive symptoms such as low mood, anhedonia, and fatigue
Reduction of symptoms of nicotine dependence and prevention of relapse
Use in patients intolerant to SSRIs due to side effect profile
Potential off-label use in adult attention-deficit hyperactivity disorder (ADHD)
Use in patients with depression who also require weight control
Management of depression in patients with sexual dysfunction or fatigue related to other antidepressants

Side Or Adverse Effects

Dry mouth and sore throat
Insomnia and sleep disturbances
Headache and dizziness
Nausea, vomiting, and gastrointestinal discomfort
Tremors and sweating
Anxiety, nervousness, or agitation
Fast or irregular heartbeat (tachycardia)
Confusion, hostility, or mood changes
Weight loss and decreased appetite
Ringing in the ears (tinnitus)
Skin rash and hypersensitivity reactions
Increased urination
Blurred vision
Seizures, especially at higher doses or in predisposed patients
Potential for suicidal ideation and behavioral changes

Precautions

Avoid use in patients with seizure disorders or history of seizures
Use with caution in patients with eating disorders such as anorexia or bulimia
Do not use during abrupt withdrawal of alcohol, benzodiazepines or sedatives
Monitor blood pressure during treatment especially in combination with nicotine replacement therapy
Be vigilant for changes in mood, worsening depression, or suicidal ideation especially in young adults
Use cautiously in patients with hepatic or renal impairment
Avoid concomitant use with monoamine oxidase inhibitors within 14 days
Inform patients that symptom improvement may take several weeks
Caution in patients with narrow-angle glaucoma due to pupillary dilation risk
Avoid abrupt discontinuation to prevent withdrawal symptoms and mood destabilization
Caution when driving or operating machinery due to potential dizziness or sedation
Adjust dose cautiously in elderly and those with comorbidities
Monitor for signs of hypertensive episodes

Warnings

Increased risk of seizures particularly at doses above recommended levels
Contraindicated in patients with seizure disorders and eating disorders
Not to be used concomitantly with other bupropion-containing products to avoid overdose
Potential for serious allergic and severe skin reactions
Risk of suicidal thoughts and behaviors primarily in patients under 24 years
Avoid use within 14 days before or after MAO inhibitor therapy
May cause manic episodes in bipolar disorder patients
Potential for high blood pressure increases especially when combined with nicotine replacement agents
May cause false positive results in amphetamine drug screening tests
Use during pregnancy only if clearly needed; unknown fetal risk
Risk of angle-closure glaucoma in susceptible individuals due to pupillary dilation
Potential for neuropsychiatric symptoms during smoking cessation therapy
Close monitoring advised during initiation and dose changes

Contraindications

History of seizure disorder or epilepsy
Current or past diagnosis of bulimia nervosa or anorexia nervosa
Abrupt discontinuation of alcohol, benzodiazepines, barbiturates, or antiepileptic drugs
Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days of MAOI therapy
Hypersensitivity or allergy to bupropion or any formulation components
Use of multiple bupropion-containing products simultaneously
Known narrow-angle glaucoma without appropriate therapy
Patients with central nervous system tumors increasing seizure risk
Use in pediatric populations due to safety concerns

Drug Interactions

Concurrent use with MAO inhibitors may cause hypertensive crisis; contraindicated
CYP2B6 inducers (e.g., carbamazepine, phenytoin, ritonavir) may decrease bupropion levels, requiring dose adjustment
Inhibits CYP2D6, increasing plasma levels of drugs metabolized by this enzyme such as certain antidepressants (paroxetine, fluoxetine), antipsychotics (haloperidol), beta-blockers (metoprolol), and some antiarrhythmics
Concurrent use with other drugs that lower seizure threshold (e.g., antipsychotics, theophylline) increases seizure risk
Digoxin levels may decrease when coadministered; monitor digoxin plasma levels
Dopaminergic agents like levodopa and amantadine may increase CNS toxicity risk
Caution when combined with CNS stimulants or serotonergic agents due to potential additive effects
Alcohol use may increase seizure risk and neuropsychiatric adverse effects
Nicotine replacement therapies may increase risk of hypertension
Drugs affecting bupropion metabolism can alter efficacy and toxicity profiles
Potential interaction with drugs altering cytochrome P450 enzymes affecting bupropion clearance

Preparations Of The Drug

Immediate-release tablets: 75 mg, 100 mg oral tablets
Sustained-release (SR) tablets: 100 mg, 150 mg, 200 mg for twice daily dosing
Extended-release (XL) tablets: 150 mg, 300 mg for once daily dosing
Brand formulations include Wellbutrin, Wellbutrin SR, Wellbutrin XL, Zyban, Aplenzin, Budeprion XL, Forfivo XL each with different release profiles
Available in oral tablet form only
Dosing strengths allow for titration based on clinical response and tolerability
Formulations designed for specific indications such as depression, smoking cessation, and seasonal affective disorder
Prescribed in divided doses for IR and SR forms, once daily for XL form
Products manufactured with access to generic equivalents in multiple strengths
Drug packaging often includes dosing instructions to avoid dose stacking and minimize seizure risk