Bupropion chemical structure
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Zyban

Bupropion (amfebutamone) is an antidepressant of the amino ketone class, chemically unrelated to tricyclics or selective serotonin reuptake inhibitors (SSRIs). It is similar in structure to the stimulant cathinone, and to phenethylamines in general. It is a chemical derivative of diethylpropion, an amphetamine-like substance used as an anorectic. Bupropion is both a dopamine reuptake inhibitor and a norepinephrine reuptake inhibitor. more...

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History

Bupropion was first synthesized by Burroughs Research in 1966, and patented by Burroughs-Wellcome (later Glaxo-Wellcome, and, as of 2000, GlaxoSmithKline) in 1974. It was approved by the FDA in 1985 and marketed under the name Wellbutrin as an antidepressant, but clinical trials indicated that incidence of seizure was two to four times greater than other antidepressants and the drug was quickly pulled from the market. It was subsequently discovered that reducing the dose by about half greatly reduced the risk of seizures. Glaxo then developed a sustained-release (SR) version of Wellbutrin which releases bupropion hydrochloride at a slower rate. The SR formulation is taken twice a day, in order to further decrease the possibility of adverse side effects and seizures. It is also available in generic form (Bupropion SR). Extended Release bupropion, Wellbutrin XL, is the most recent formulation of bupropion and is taken orally once a day. Because of this altered mechanism of delivery and reduced dosing, incidence of seizures with bupropion is comparable to, and in some cases, lower than that of other antidepressants.

In 1997, bupropion HCl was approved by the FDA for use as a smoking cessation aid. Glaxo subsequently marketed the drug under the name Zyban to help people stop smoking tobacco by reducing the severity of craving and addiction/withdrawal symptoms. It can be used in combination with nicotine replacement therapies. Bupropion treatment course lasts for seven to twelve weeks, with the patient halting the use of tobacco around ten days into the course.

Bupropion is also being investigated as a weight loss drug.

Mode of action

Bupropion is a selective catecholamine (norepinephrine and dopamine) reuptake inhibitor. It has only a small effect on serotonin reuptake. It does not inhibit MAO. The actual mechanism behind bupropion's action is not known, but it is thought to be due to the effects on dopaminergic and noradrenergic mechanisms.

Pharmacokinetics

Bupropion is metabolised in the liver. It has at least three active metabolites: hydroxybupropion, threohydrobupropion and erythrohydrobupropion. These active metabolites are further metabolised to inactive metabolites and eliminated through excretion into the urine. The half-life of bupropion is 20 hours as is hydroxybupropion's. Threohydrobupropion's half-life is 37 hours and erythrohydrobupropion's 33 hours.

Chronic hepatotoxicity in animals

In rats receiving large doses of bupropion chronically, there was an increase in incidence of hepatic hyperplastic nodules and hepatocellular hypertrophy. In dogs receiving large doses of bupropion chronically, various histologic changes were seen in the liver, and laboratory tests suggesting mild hepatocellular injury were noted.

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Does long-term bupropion use prevent smoking relapse after initial success at quitting smoking? - Zyban - Poems
From Journal of Family Practice, 2/1/02 by Thomas A. Barringer

Hays JT, Hurt RD, Rigotti NA, et al. Sustained release bupropion for pharmacologic relapse after smoking cessation. Ann Intern Med 2001; 135:423-33.

* BACKGROUND Regardless of the intervention used, relapse after initial smoking cessation occurs in 70% to 80% of patients within 6 to 12 months. The investigators studied whether continuing bupropion treatment after initial success would decrease the relapse rate.

* POPULATION STUDIED The investigators enrolled 784 men and women, aged 18 years or older, who had smoked 15 cigarettes or more per day for the previous year. Participants were motivated to stop smoking and were generally in good health. The investigators excluded persons dependent on alcohol or other non-nicotine substances in the previous year, those using psychotropic medications or with a history of bupropion use, those currently using tobacco products other than cigarettes, and those currently using another therapy for smoking cessation.

* STUDY DESIGN AND VALIDITY This was a multicenter randomized double-blind placebo-controlled trial. All participants were given self-help material and took 300 mg bupropion sustained-release daily for 7 weeks. The subjects were instructed to set a target quit date 1 week after initiating treatment. Participants who had abstained from smoking cigarettes at week 7 were randomized to receive either bupropion or placebo for a total of 1 year. Allocation to treatment group was concealed and intention-to-treat analyses were performed. Participants returned for 14 visits during the first year (the medication phase) and for 5 visits during the follow-up year. All participants received the same educational material and counseling at each visit throughout the study.

The 40% long-term success rate after cessation is higher than that of previous studies. The 55% to 60% abstinence rate of those taking bupropion may pose an unrealistic expectation for care providers. These results were obtained in a select group of smokers who were highly motivated, who were intensely monitored (20 clinic visits over 2 years), and who received behavioral counseling at every visit.

* OUTCOMES MEASURED The study had 3 primary outcomes: (1) abstinence the week preceding each visit during the first year; (2) continuous abstinence during medication treatment; and (3) time to first relapse. Smoking status was defined by self-report of abstinence over the previous 7 days, confirmed with an expired air / carbon monoxide measurement at each visit. Relapse was defined by self-report, by expired air / carbon monoxide levels, or by missing 2 or more consecutive visits. Participants who were abstinent at every visit were classified as continuously abstinent.

* RESULTS Of the 784 participants enrolled in the open-label bupropion phase of the study, 461 (58.8%) were abstinent at week 7. Of these, 429 were randomized to receive placebo or bupropion for 45 weeks. A total of 347 (80.9%) remained in the study through the first year. Most participants (317, 73.9%) completed the entire 2 years of the study. Dropout rates were similar in the treated and untreated groups. At the end of 1 year, 55.1% of the treated patients were not smoking, compared with 42.3% in the placebo group (P= .001, NNT=8). At 18 months, significantly more treated patients were still not smoking (47.7% vs 37.7%, number needed to treat = 10). At the end of 2 years, however, abstinence rates were similar for the 2 groups (41.6% vs 40%). The drug was well tolerated. Insomnia and headache were the most common adverse effects.

RECOMMENDATIONS FOR CLINICAL PRACTICE

Highly motivated patients who stop smoking during the standard 7-week bupropion program are likely to maintain abstinence as long as they continue to take the drug, at least for 1 year. Once they have discontinued the drug, however, the relapse rate in this group is the same as for those in the standard program: It is reasonable to offer bupropion indefinitely to certain patients who are able to quit smoking after the standard program--those who can afford it or perhaps those for whom another indication to take bupropion is identified--as long as the clinician informs them of the available data on relapse after they have ended their participation in the program.

COPYRIGHT 2002 Appleton & Lange
COPYRIGHT 2002 Gale Group

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