Wellbutrin XL, SR

Wellbutrin XL (extended-release) is used to relieve mental depression. It is also used to prevent episodes of seasonal affective disorder (form of depression occurring mainly during the autumn and winter months). This medication effectively treats depression characterized by reduced energy, pleasure and interest, with low risk of weight gain sexual side effects.

This antidepressant is often prescribed for depression when selective serotonin reuptake inhibitors (SSRIs) or tricyclic antidepressants (TCAs) cannot be used or are not effective.

Dosing: The starting dose is 150 mg per day, which your doctor may increase to the usual adult dose of 300 mg per day. The maximum dosage is 450 mg per day. Always make sure that you take Wellbutrin XL as prescribed by your doctor.

Although not an approved indication, the combination of Wellbutrin and either an SSRI or an SNRI is generally well tolerated and can boost antidepressant response. Combining two antidepressants has become a common strategy in the treatment of resistant depression. The results of clinical study have shown that when the patient fails to respond to an SSRI or venlafaxine, an addition of Wellbutrin SR can increase the chances of response [5].

Wellbutrin appears to significantly affect dopaminergic neurotransmission and may help with fatigue and sexual dysfunction induced by SSRIs of SNRIs. A study by Papakostas and associates examined the impact of bupropion vs SSRIs on sleepiness and fatigue in patients with depression. The investigators pooled data from 6 double-blind, randomized clinical trials and found greater improvements in fatigue scores among both bupropion-treated and SSRI-treated groups than placebo-treated patients, and greater improvements in fatigue scores among bupropion-treated than SSRI-treated patients [6].

Wellbutrin may reverse SSRI-induced sexual dysfunction due to its dopaminergic effect. In addition to the SSRI produces an increase in desire to engage in sexual activity and frequency of engaging in sexual activity [7].

• Metabolism: Extensively metabolized by hydroxylation or oxidation in the liver. CYP2B6 is involved in formation of hydroxybupropion (50% as potent as bupropion). The other 2 main metabolites are threohydrobupropion and erythrohydrobupropion, which are 20% as potent as bupropion.
• Elimination half-life: about 21 hr, about 20 hr (hydroxybupropion), about 37 hr (threohydrobupropion), and about 33 hr (erythrohydrobupropion).
• Excretion: 87% excreted in urine, 10% in feces, and 0.5% as unchanged drug.

• once a day dosage regimen
• low risk of sexual dysfunction [2]: does not lower libido, produce impotence or impair orgasms
• low risk of weight gain
• decreased appetite and weight loss (however, may be a harmful effect for anorectic persons)
• low potential for triggering mania in the bipolar disorder

• frequently cause agitation, anxiety, and insomnia (addition of a sedative agent or discontinuation of therapy may be required; gradual escalation of dose may minimize symptoms)
• risk of seizures
• risk of hypertension
• high potential for interactions; it is cytochrome P450-2D6 (CYP2D6) inhibitor

Wellbutrin XL contains the same active ingredient as Wellbutrin SR, but XL is formulated in an extended-release, once-daily tablet. This means that with XL formulation, you can take one tablet in the morning, continue with your daily activities, and not worry about remembering to take a second dose.

Both formulations are bioequivalent in terms of systemic exposure to bupropion, but differ in their pharmacokinetics and dosing.

• attention-deficit/hyperactivity disorder (ADHD)
• depression associated with bipolar disorder (in combination with mood stabilizers)
• enhancement of weight loss
• augmenting a partial response to SSRIs

The mechanism of activity is not fully understood. It is a relatively weak inhibitor of the neuronal uptake of norepinephrine and dopamine, and does not inhibit monoamine oxidase or the reuptake of serotonin. Metabolite inhibits the reuptake of norepinephrine. The primary mechanism of action is thought to be dopaminergic and/or noradrenergic.

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• 1. U.S. FDA. Wellbutrin XL Prescribing Information
• 2. Labbate LA, Brodrick PS, Nelson RP, Lydiard RB, Arana GW. Effects of bupropion sustained-release on sexual functioning and nocturnal erections in healthy men. J Clin Psychopharmacol. 2001 Feb;21(1):99-103. PubMed