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Orexigen Therapeutics, Inc.

Drug Names(s): Excalia, zonisamide and bupropion

Description: Empatic is a proprietary combination of bupropion, a dopamine and norepinephrine reuptake inhibitor, plus zonisamide, an anticonvulsant medication. Bupropion and zonisamide are thought to act on the regulatory cells of the hypothalamus to reduce food intake and increase energy expenditure.

Proopiomelanocortin (POMC) neurons in hypothalamus express receptors for the hormone leptin (involved in adjusting food intake and energy expenditure to maintain constant levels of fat) and play a central role in the control of energy homeostasis and body weight regulation. Fat cells release leptin, which enter the brain to provide information about the body's energy stores. Stimulation of leptin receptors in POMC neurons leads to the release of alpha-MSH which, in turn, stimulate MC4 receptors to decrease food intake and increase metabolic rate. Neuropeptide Y (NPY)/agouti-related protein (AgRP) neurons release AgRP, which acts in an opposite manner.

Blockade of dopamine and norepinephrine re-uptake by bupropion increases levels of these neurotransmitters, which is thought to cause release of alpha-MSH, but reduced secretion of AgRP, thereby reducing appetitite and increasing metabolism. Zonisamide is thought to also increase monoamines.

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