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Cells in the body release histamine during several types of allergic reactions. When histamine binds to its receptors on other cells, it stimulates changes within the cells that lead to release of other chemicals that cause sneezing, itching, and increased mucus production. Antihistamines such as promethazine compete with histamine for one of the receptors for histamine (the H1 receptor) on cells; however, when antihistamines bind to the receptors they do not stimulate the cells. Instead, they prevent histamine from binding and stimulating the cells. Promethazine also blocks the action of acetylcholine, a neurotransmitter that nerves use to communicate with one another, on its receptors (anticholinergic effect), and this may explain its benefit in reducing the nausea of motion sickness. It is used as a sedative because it causes drowsiness as a side effect. The cough suppressant effects may be due to is anticholinergic effects.
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Dr. Ogbru received his Doctorate in Pharmacy from the University of the Pacific School of Pharmacy in 1995. He completed a Pharmacy Practice Residency at the University of Arizona/University Medical Center in 1996. He was a Professor of Pharmacy Practice and a Regional Clerkship Coordinator for the University of the Pacific School of Pharmacy from 1996-99.
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GENERIC NAME: promethazine and codeine BRAND NAME: (Phenergan with Codeine: This brand no longer is available in the U.S.) DRUG CLASS AND MECHANISM: Promethazine is in a class of drugs called phenothiazines which also includes chlorpromazine (Thorazine) and trifluoperazine (Sazine); however, unlike the other drugs in this class, promethazine is not used as an anti-psychotic but rather as an anti-histamine, sedative, antiemetic (anti-nausea), and cough suppressant.
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Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.
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