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(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.


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.


A drug that prevents or diminishes the effect of histamine; used in treating allergic reactions and common-cold symptoms.


any drug that neutralizes the effects of histamine, used esp in the treatment of allergies
References in periodicals archive ?
In conclusion, we found that pheniramine maleate which is an antihistaminic is more effective than lidocain and can be considered as an alternative method to prevent fentanyl induced cough during anesthesia induction.
2003) The antioxidative and antihistaminic properties of quercetin in ethanol-induced gastric lesions.
Topical anti-inflammatory, antihistaminic, analgesics, anesthetics agents, immunomodulators, immunosuppressants, as well as steroids agents [11, 13] are prescribed based on the severity of RAS 1,3,14].
The company manufactures APIs in several therapeutic categories, including Antihistaminic, Antihypertensive, Antithrombotic and Anticonvulsant.
Scouring through The Journal of Pharmacy and Pharmacology for instance, a researcher from, say, Harvard University could spot a topic such as "Evaluation of antihistaminic activity of piper betel leaf in guinea pig".
In cases of older patients, a sedative antihistaminic is preferred to the non-sedating forms so as to prevent the patient from continuously scratching the affected area.
It is also used as an antibacterial, antipyretic, antihistaminic, analgesic, insecticidal, ovicidal, feeding deterrent, growth inhibitor and morphogenetic agent (12-21).
Mast Cell Stabilizing, Antianaphylactic and Antihistaminic Activity of Coccinia grandis Fruits in Asthma.
Fully buffered ascorbates and flavonoid/flavonol complexes described here work synergistically, and are antihistaminic and hormone sparing.
Combination mast cell stabilizers and antihistamines, which combine mechanisms of both antihistaminic and mast cell stabilization in a single drug, are the most recently developed drugs for topical treatment of ocular allergies.
prescription Analgesics 49 35 Analgesic opiates 9 0 Antibiotics 54 35 Antifungal/antiviral/antiparasitics 18 44 Fixed combinations 29 59 Blood pressure medication 26 19 Oral antidiabetics 9 78 Proton pump inhibitors/antiacids/ 15 47 histamine H2-receptor antagonists Antidiarrheals 7 57 Antihistaminic 7 43 Cough medicine 11 18 Anticoagulants + antiplatelet drugs 2 100 Contraceptives 8 0 Bronchodilators 4 50 Antiepileptic/antidepressants/anxiolytics 6 67 Osteoporosis treatment 2 50 Thyroid medicine 6 17 Cholesterol lowering medication 3 67 Vitamins/minerals/other nutrients 13 46 Testosterone 1 0 Corticosteroids 7 29 Other OTC medicines (a) 25 40 Total (all types) 311 38 End-user's country of residence Mexico % with Medications type No.