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Related to Antihistaminergic: H1 receptor antagonist, H1 antihistamine


(ăn'tĭhĭs`təmēn), any one of a group of compounds having various chemical structures and characterized by the ability to antagonize the effects of histaminehistamine
, organic compound derived in the body from the amino acid histidine by the removal of a carboxyl group (COOH). Although found in many plant and animal tissues, histamine is specifically important in human physiology because it is one of the chemicals released from
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. Their principal use in medicine is in the control of allergies such as hay fever and hives. Some antihistamines are also useful as sedatives and for the prevention of motion sickness; others, such as fexofenadine (Allegra) and loratadine (Claritin) are nonsedating.
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A type of drug that inhibits the combination of histamine with histamine receptors. These drugs are termed either H-1 or H-2 receptor antagonists depending on which type of histamine receptor is involved. H-1 receptor antagonists are used largely for treating allergies, and H-2 receptor antagonists are used to treat peptic ulcer disease and related conditions. See Histamine

The primary therapeutic use of H-1 receptor antagonists is to antagonize the effects of histamine released from cells by antigen-antibody reactions; they can thus inhibit histamine-induced effects, such as bronchoconstriction, skin reactions, for example, wheals and itching, and nasal inflammation. These drugs, therefore, are quite effective in reducing allergy signs and symptoms, especially if they are administered before contact with the relevant antigen; however they are not effective in treating asthma. Their effects vary widely, both among the drugs and from individual to individual; in young children excitement may be seen. Another common set of effects caused by many of these drugs, including dry mouth, blurred vision, and urinary retention, can be ascribed to their anticholinergic actions. H-1 receptor antagonists have low toxicity. The chief adverse effect is sedation. Overdoses of H-1 receptor antagonists may be associated with excitement or depression, and although there is no pharmacologic antidote for these drugs, good supportive care should be adequate in managing cases of poisoning. See Allergy, Antigen-antibody reaction

H-2 receptor antagonists are much newer. Histamine stimulates gastric acid secretion by combining with H-2 receptors. By preventing this combination, H-2 antagonists can reduce acid secretion in the stomach, an effect that makes these drugs useful in managing various conditions, such as peptic ulcer disease.

Other conditions in which H-2 antagonists are used to lower gastric acidity include reflux esophagitis, stress ulcers, and hypersecretory states such as the Zollinger-Ellison syndrome, in which tumor cells secrete large amounts of the hormone gastrin, which stimulates gastric acid secretion. In these conditions, administration of H-2 antagonists reduces symptoms and promotes healing.

The toxicity of H-2 antagonists is quite low, and adverse effects are reported by only 1-2% of patients. The most common side effects are gastrointestinal upsets, including nausea, vomiting, and diarrhea.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


A drug that prevents or diminishes the effect of histamine; used in treating allergic reactions and common-cold symptoms.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


any drug that neutralizes the effects of histamine, used esp in the treatment of allergies
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
(40) Adverse effects of mood stabilizers and/or various atypical antipsychotic agents have been reported in specific domains, including antihistaminergic (sedation, weight gain), anticholinergic (dry mouth, constipation), alpha-1 blockade (dizziness, orthostasis), dopamine antagonism (hyperprolactinemia, psychomotor slowing, extrapyramidal symptoms [EPS]), and increased serotonergic effect (sexual dysfunction).
Animal studies have shown anticholinergic and antihistaminergic activity with doxepin.
* High-potency antipsychotics are preferred during pregnancy because they are less likely to have associated anticholinergic, antihistaminergic, or hypotensive effects.
The TCAS cause a broad spectrum of adverse effects, including anticholinergic effects (eg, dry mouth, constipation, blurred vision, urinary retention, impaired cognition), antihistaminergic effects (eg, sedation, weight gain), serotonergic effects (eg, sexual dysfunction), and in overdose, direct cardiotoxic effects similar to those with quinidine antiarrhythmics (Table5).[58-61] Unfortunately, in a patient population focused on somatic complaints, even minor, nuisance side effects may limit compliance with a prescribed drug regimen.
The mechanism of action of bupropion is not known but may possibly be related to relatively weak effects on noradrenergic, dopaminergic, and serotonergic systems., Bupropion is not associated with the anticholinergic, antihistaminergic, or cardiac effects of the TCAs or venlafaxine.