an·ti·his·ta·mine .ant-i-'his-tə-.mēn, .an-.tī-, -mən adj tending to block or counteract the physiological action of histamine <human blood lacks \antihistamine activity>
antihistamine n any of various compounds that oppose the actions of histamine and are used esp. for treating allergic reactions (as hay fever), cold symptoms, and motion sickness

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a drug that inhibits the action of histamine in the body by blocking the receptors for histamine, of which there are two types: H1 and H2. When stimulated by histamine, H1 receptors may produce such allergic reactions as hay fever, pruritus (itching), and urticaria (nettle rash). Antihistamines that block H1 receptors (H1-receptor antagonists), for example acrivastine, azatadine, and chlorphenamine, are used to relieve these conditions. Many H1-receptor antagonists, e.g. cyclizine and promethazine, also have strong antiemetic activity and are used to prevent motion sickness. The most common side-effect of these drugs, especially the older antihistamines (e.g. azatadine, brompheniramine, diphenhydramine, promethazine), is drowsiness and because of this they are sometimes used to promote sleep. Newer antihistamines (e.g. acrivastine, cetirizine (Zirtek), loratidine (Clarityn), terfenadine) are less sedating. Other side-effects include dizziness, blurred vision, tremors, digestive upsets, and lack of muscular coordination.
H2 receptors are found mainly in the stomach, where stimulation by histamine causes secretion of acid gastric juice. H2-receptor antagonists (e.g. cimetidine, nizatidine, ranitidine, and famotidine) block these receptors and reduce gastric acid secretion; they are used in the treatment of peptic ulcer and gastro-oesophageal reflux disease.

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an·ti·his·ta·mine (an″te-) (an″ti-hisґtə-mēn) an agent that counteracts the action of histamine. While the term can broadly include any agent that blocks any histamine receptor, in practice it is usually used to denote those blocking H1 receptors (H1 receptor antagonists), which are the drugs conventionally used to treat allergic reactions and are also components of many cough and cold preparations. Agents blocking H2 receptors are usually called histamine H2 receptor antagonists, and include the agents used to inhibit gastric secretion in peptic ulcer. See also histamine.

Medical dictionary. 2011.

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Look at other dictionaries:

  • antihistamine — (n.) 1933, from ANTI (Cf. anti ) + HISTAMINE (Cf. histamine) …   Etymology dictionary

  • antihistamine — ► NOUN ▪ a drug that counteracts the effects of histamine, used in treating allergies …   English terms dictionary

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  • antihistamine — UK [ˌæntɪˈhɪstəmiːn] / US [ˌæntɪˈhɪstəˌmɪn] noun [countable/uncountable] Word forms antihistamine : singular antihistamine plural antihistamines medical a drug used to treat an allergy (= a bad reaction to something you swallow or touch) …   English dictionary

  • antihistamine — noun Date: 1946 any of various compounds that counteract histamine in the body and that are used for treating allergic reactions (as hay fever) and cold symptoms • antihistamine adjective • antihistaminic adjective or noun …   New Collegiate Dictionary

  • antihistamine — [[t]æ̱ntihɪ̱stəmɪn[/t]] antihistamines also anti histamine N COUNT An antihistamine is a drug that is used to treat allergies …   English dictionary

  • antihistamine —    An exogenous agent that inhibits the release of histamine, the amino acid derivative that stimulates vasodilation and permeability under many circumstances, particularly tissue irritation. The most common type of antihistamine, the H1 receptor …   Herbal-medical glossary

  • antihistamine — /an ti his teuh meen , min/, n. Biochem., Pharm. any of certain compounds or medicines that neutralize or inhibit the effect of histamine in the body, used chiefly in the treatment of allergic disorders and colds. [1930 35; ANTI + HISTAMINE] * *… …   Universalium

  • antihistamine — noun A drug or substance that counteracts the effects of a histamine. Commonly used to alleviate the symptoms of hay fever and other allergies …   Wiktionary

  • antihistamine — an|ti|his|ta|mine [ˌæntıˈhıstəmi:n, mın] n [U and C] a drug that is used to treat an ↑allergy (=an unpleasant reaction to particular foods, substances etc) …   Dictionary of contemporary English

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