Bupropion action

The mechanism of action of most of the miscellaneous antidepressants is not clearly understood. Examples of this group of drugs include fluoxetine (Prozac) and bupropion (Wellbutrin). 

Nortriptyline. Nortriptyhne, a tricychc antidepressant, has been shown in double-blind, placebo-controlled randomized trials to be superior to placebo for smoking cessation (Prochazka et al. 1998). Nortriptyline appears to have efficacy comparable to that of bupropion for smoking cessation (Hall et al. 2002). The efficacy of this agent may be improved with more intensive behavioral therapies (Hall et al. 1998). Nortriptyline s mechanism of action is thought to relate to its noradrenergic and serotonergic reuptake blockade, because these two neurotransmitters have been implicated in the neurobiology of nicotine dependence. Side effects of nortiptyline are typical of tricyclic antidepressants and include dry mouth, blurred vision, constipation, and orthostatic hypotension. Nortriptyline appears to have some utility for smokers with a past history of major depression, and it can be recommended as a second-... 

The tricyclic antidepressants (TCAs), such as imipramine, can alleviate symptoms of ADHD. Like bupropion, TCAs likely will improve symptoms associated with comorbid anxiety and depression. The mechanism of action of TCAs is in blocking norepinephrine transporters, thus increasing norepinephrine concentrations in the synapse the increase in norepinephrine is believed to alleviate the symptoms of ADHD. TCAs have been demonstrated to be an effective non-stimulant option for ADHD but less effective than stimulants. However, their use in ADHD has declined owing to case reports of sudden death and anticholinergic side effects6,13 (Table 39-3). Further, TCAs may lower seizure threshold and increase the risk of car-diotoxicity, (e.g., arrythmias). Patients starting on TCAs should have a baseline and routine electrocardiograms. 

Bupropion s most potent neurochemical action is blockade of DA reuptake it blocks the reuptake of NE to a lesser extent. 

After more than a decade of use, bupropion (24) is considered a safe and effective antidepressant, suitable for use as first-line treatment. In addition, it is approved for smoking cessation and seasonal affective disorder. It is also prescribed off-label to treat the sexual dysfunction induced by SSRIs. Bupropion is often referred to as an atypical antidepressant and has much lower affinity for the monoamine transporters compared with other monoamine reuptake inhibitors. The mechanism of action of bupropion is still uncertain but may be related to inhibition of dopamine and norepinephrine reuptake transporters as a result of active metabolites [71,72]. In a recently reported clinical trial, bupropion extended release (XL) had a sexual tolerability profile significantly better than that of escitalopram with similar re-... 

Triple reuptake inhibitors (TRIs), which inhibit reuptake at all three transporters, have attracted considerable interest in recent years [77]. The involvement of dopamine reuptake in the etiology of depression and other CNS disorders has been recognized [29,30]. As a result, TRIs have been proposed to offer a faster onset of action and improved efficacy for depression over currently prescribed single or dual action monoamine reuptake inhibitors. Historically, the mesocorticolimbic dopamine pathway is thought to mediate the anhedonia and lack of motivation observed in depressed patients [78,79]. In addition, methylphenidate, both immediate release and extended release formula, has been found to be effective as an augmenting agent in treatment-resistant depression [4]. Furthermore, clinical studies using the combination of bupropion and an SSRI or SNRI have showed improved efficacy for the treatment of MDD in patients refractory to the treatment with SSRIs, SNRIs, or bupropion alone [5,80,81]. 

Tricyclic drugs have, as the name implies, a three-ring structure, and interfere with reuptake of norepinephrine and/or serotonin into axon terminals. Tricyclic drugs include imipramine (Tofranil), amitriptyline (Elavil), clomipramine (Anafranil), and nortriptyline (Pamelor, Aventil). Tricyclics have the occasional but unfortunate cardiovascular side effects of arrhythmia and postural hypotension. Newer, nontricyclic antidepressants have been developed that are collectively referred to as SSRIs. These have a potent and selective action on serotonin, and lack the cardiovascular side effects of the tricyclics. These include fluoxetine (Prozac), paroxetine (Paxil), sertraline (Zoloft), and fluvoxamine (Luvox). A fifth SSRI, citalopram (Celexa) has been used in Europe and has recently been approved in the United States. Venlafaxine (Effexor) blocks reuptake of norepinephrine and serotonin, while bupropion (Wellbutrin) acts on both dopamine and norepinephrine. 

Sexual function One of the potential benefits of hypericum is the apparent reduced or lack of adverse effects upon sexual function, compared to pharmaceutical antidepressants. The SSRIs are particularly notorious for inhibition of sexual function, whereas antidepressants with dopaminergic actions (e.g., bupropion) do not, and may actually enhance sexual function (Rosen et al. 1999 Piazza et al. 1997). Anecdotal reports and the fact that there are no clinical reports of sexual dysfunction with hypericum is encouraging, but it remains to be tested empirically. 

Costall B, Jones BJ, Kelly ME, Naylor RJ, Onaivi ES, Tyers MB (1990b) Sites of action of ondansetron to inhibit withdrawal from drugs of abuse. Pharmacol Biochem Behav 36 97-104 Cryan JF, Bruijnzeel AW, Skjei KL, Markou A (2003) Bupropion enhances brain reward function and reverses the affective and somatic aspects of nicotine withdrawal in the rat. Psychopharmacology 168 347-358... 

Bupropion is an atypical antidepressant drug that is the only nonnicotine-based prescription medicine approved for smoking cessation by the FDA. Its mechanism of action is presumed to be mediated by its capacity to block neuronal reuptake of dopamine and/or norepinephrine (Fiore et al. 2000). Relative to other antidepressants, bupropion has a relatively high affinity for the dopamine transporter (Baldessarini 2001). There is also evidence that bupropion acts as a functional nicotine antagonist, suggesting another potential mechanism by which bupropion could reduce smoking rates (Slemmer et al. 2000). 

Bupropion (Weiibutrin, Zyban). Bupropion is an antidepressant that is also FDA approved as a treatment for smoking cessation. It is marketed as an antidepressant as Weiibutrin and for the treatment of nicotine dependence as Zyban. Its mechanism of action in this regard is obscure, but it may act on dopamine and/or norepinephrine systems. 

Another widely practiced strategy to treat sexual dysfunction is the addition of pro-noradrenergic or pro-dopaminergic medications such as dopamine agonists or psychostimulants. The addition of bupropion is also believed to be effective but its mechanism of action remains obscure. 

Pharmacology Bupropion is a nonnicotine aid to smoking cessation. The mechanism by which bupropion enhances the ability of patients to abstain from smoking is unknown. However, it is presumed that this action is mediated by noradrenergic or dopaminergic mechanisms. 

The role of dopamine is discussed more thoroughly in Finder, Chapter 14, in this volume. Several antidepressants are thought to have enhanced antidepressant action attributed to extra effects on the dopamine system. Bupropion, which is available as an antidepressant in the United States only, has an indirect effect on dopamine. An appropriate minimum effective dose was not established in the early clinical trial development program, and the rather high doses used in clinical practice may have contributed to the number of reports of convulsions. The rate, which is acceptable at lower doses of 450 mg/day, rises to unacceptable levels at higher doses [J. A. Johnston et al. 1991). 

This lack of information may well relate to bupropion s complex metabolism, whereby biologically active metabolites predominate several-fold over the parent compound these metabolites may ultimately prove to be the basis for therapeutic effects [Golden et al. 1988]. Furthermore, because the full spectrum of action of the metabolites has not been explored, it is difficult to confidently characterize the primary biochemical action of bupropion as noradrenergic. One must therefore be cautious in interpreting any distinct aspects of bupropion s clinical actions as reflecting some noradrenergic mechanisms. And to our knowledge, bupropion is unique in that no other compound available for use in humans has a similar overall profile of preclini-cal and clinical biochemical effects. 

Although the efficacy of tricyclic antidepressants in the treatment of unipolar depression is beyond reproach, the side-effect profile of these agents makes them less desirable as first-line therapeutic agents. Introduction of selective serotonin reuptake inhibitors (SSRIs) such as fluoxetine, paroxetine, sertraline, citalopram and fluvoxamine in the past decade has revolutionized the treatment of depression universally. The side-effect profile of SSRIs, such as nausea, diarrhea and sexual dysfunction, is considerably more benign than that of tricyclic drugs. Multiple controlled trials have proven the efficacy of SSRIs vs. placebo (Nemeroff, 1994). Recently, a number of SNRIs (serotonin and noradrenaline reuptake inhibitors) and so-called atypical antidepressants have been marketed that may have additional advantages over SSRIs, such as more rapid onset of action (venlafaxine. mirtazapine) and low sexual side-effect potential ( bupropion, nefazodone). Additionally, it appears that venlafaxine may be more efficacious in cases of treatment-refractory depression (Clerc et al., 1994 Fatemi et al., 1999). Finally, in a recent report (Thase et al., 2001),... 

Bupropion appears to be pharmacologically unique relative to other conventional antidepressants and most closely resembles the action of psychostimulants. 

Consistent with its most potent known mechanism of action, bupropion is an indirect dopamine agonist via its inhibition of the neuronal uptake pump for dopamine (503, 504). Hence, bupropion can potentiate the effects of other dopamine agonists. This interaction does not typically cause serious problems and may even be advantageous in specific instances such as patients with Parkinson s disease plus a depressive disorder. Because of its ability to inhibit NE uptake, bupropion would be prone to the same interactions as NSRIs such as desipramine and reboxetine. 

Preskorn SH. Bupropion what mechanism of action J Pract Psychiatry Behav Heaith 2000 6 39-44. 

Ferris R, Maxwell R, Cooper B, et al. Neurochemical and neuropharmacological investigations into the mechanisms of action and bupropion hydrochloride —a new atypical antidepressant agent. In Costa E, Racogoni B, eds. Typical and atypical antidepressants molecular mechanisms. New York Raven Press, 1982. 

The actions of bupropion remain poorly understood. Bupropion and its major metabolite hydroxybupropion are modest-to-moderate inhibitors of norepinephrine and dopamine reuptake in animal studies. However, these effects seem less than are typically associated with antidepressant benefit. A more significant effect of bupropion is presynaptic release of catecholamines. In animal studies, bupropion appears to substantially increase the presynaptic availability of norepinephrine and dopamine to a lesser extent. Bupropion has virtually no direct effects on the serotonin system. 

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