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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COPD Patients Fare Best With Zyban for Smoking Cessation - Brief Article
From Family Pratice News, 3/15/01

SAN FRANCISCO -- Smokers with chronic obstructive pulmonary disease are more likely to kick the habit with the help of sustained-release bupropion, Dr. Donald P. Tashkin reported at the annual meeting of the American College of Chest Physicians.

Women, heavier smokers, and patients with moderate, rather than mild, COPD got the greatest benefit from treatment with sustained-release bupropion (Zyban) in a randomized, placebo-controlled study that included 411 patients, said Dr. Tashkin of the University of California, Los Angeles.

Previous data had established that Zyban was an effective first-line aid for smokers without COPD who were trying to quit, he noted.

All patients in the current study had mild (stage I) or moderate (stage II) COPD diagnosed by spirometry and were randomized to 12 weeks of treatment with Zyban (206 patients) or placebo (205 patients) and followed for 26 weeks. Patients in both treatment arms had smoked 25-2 6 years and made more than three attempts to quit, on average.

Patient diaries and tests of exhaled carbon dioxide at clinic visits showed that patients using Zyban were more likely to abstain from smoking. At 4 weeks, 32% in the Zyban group and 18% in the placebo group were abstinent, rates that fell by week 26 to 16% of patients in the Zyban group and 9% on placebo, Dr. Tashkin said.

Patients with mild COPD found it easier to quit than did patients with moderate COPD-quir rates were higher for patients with stage I disease in both the Zyban and placebo groups, compared with patients with stage II COPD. Among smokers with stage I COPD, 29% on Zyban and 18% on placebo achieved abstinence. Quit rates were 19% and 7%, respectively, for patients with stage II COPD.

Zyban proved to be more helpful for patients with stage II COPD, increasing the odds of abstinence more than threefold if they took Zyban rather than placebo. Among patients with stage I COPD, Zyban doubled the odds of abstinence, compared with the placebo group, Dr. Tashkin reported.

The difference in abstinence rates between Zyban and placebo was greater for women with COPD than for men. The drug nearly tripled the odds of quitting for women and doubled the odds of quitting for men.

Heavier smokers (those with more than a 30-pack-year history of smoking) were more than twice as likely to quit using Zyban, compared with placebo, and lighter smokers improved their chances of quitting by an odds ratio of 1.5 using Zyban instead of placebo.

An equal proportion of patients in each group discontinued treatment: 14 with Zyban and 13 with placebo. Patients on placebo had more craving for cigarettes and more withdrawal symptoms such as anger, anxiety, sadness, and difficulty concentrating.

Age (older or younger than 60 years) did not affect abstinence rates, Dr. Tashkin said.

Rates of insomnia were higher in the Zyban group in the first few weeks but then leveled off, Dr. Tashkin said. Overall, insomnia affected 25% of patients on Zyban and 13% of patients on placebo but rarely caused discontinuation of treatment.

COPYRIGHT 2001 International Medical News Group
COPYRIGHT 2001 Gale Group

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