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Page: Mode of Action
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Bupropion is a dopamine and norepinephrine reuptake inhibitor. It is about twice as potent an inhibitor of dopamine uptake than norepinephrine uptake. As bupropion is rapidly converted in the body into several metabolites with differing activity, its action cannot be understood without understanding its metabolism. Occupancy of dopamine transporter (DAT) by bupropion and its metabolites in human brain measured by positron emission tomography was 6–22% according to an independent study and 12–35% according to GSK researchers. Based on the analogy with serotonin reuptake inhibitors, higher than 50% inhibition of DAT would be needed for the dopamine reuptake mechanism to be a major mechanism of bupropion action. Bupropion does not inhibit MAO (i.e. is not a MAOI) and serotonin reuptake. However, it has been shown to indirectly enhance firing of serotonergic neurons (via activation of downstream norepinephrine flow). Bupropion has also been shown to act as a noncompetitive ?3?4 nicotinic antagonist. The degree of inhibition of ?3?4-receptors correlates well with the decrease of self-administration of morphine and metamphetamine in rats, and may be relevant to the effect of bupropion on nicotine addiction.
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