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antihistamine (ănˌtĭhĭsˈtəmēn), any one of a group of compounds having various chemical structures and characterized by the ability to antagonize the effects of histamine. 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
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Our study provides useful information to plan a suitable educational intervention for rationale antihistaminic use and to minimize adverse effect.
Present study has been targeted to develop the rapid and accurate spectrophotometric methods for the determination of five antihistaminic drugs; promethazine, diphenhydramine, desloratadine, levocetirizine, and loratadine.
A detail history revealed that, she used to develop that kind of rash in each month, began 3-4 days before starting of menstruation and subsided spontaneously or with antihistaminic within 4-5 days after stoppage of menstruation.
This rash delayed the patient departure from the hospital but had a favorable response to medical treatment with IV corticosteroid and antihistaminic. 127 ERCPs were performed on 75 iodine allergic patients.
He is currently on antihistaminic. Attacks in mild form are still present.
MRS resembles angioedema, but it can be differentiated with the lack of response to antihistaminic drugs, tendency to last longer and by causing fibrosis in the involved tissues (18).
Other works demonstrated that the antisecretory action of the aqueous extract occurs through a mechanism common to both antihistaminic and anticholinergic pathways [18].
However, participants who were on treatment with antidepressants, antihistaminic, and antihypertensive, were edentulous or had any systemic illnesses, or underwent radiotherapy to head and neck regions were excluded from the study.
The seeds and extracts have antioxidant [3], antidiabetic [4], antihistaminic [5], antihypertensive [6], antiinflammatory, analgesic [7], antimicrobial [8], and antitumor [9] effects.
A limited number of studies have investigated the clinical properties and antihistaminic treatment responses of children with urticaria in the literature.
The patient was put on topical steroid and oral antihistaminic treatment.