antihistamine

antihistamine /an·ti·his·ta·mine/ (-his´tah-mēn) an agent that counteracts the action of histamine; usually used for agents blocking H1 receptors (H) and used to treat allergic reactions and as components of cough and cold preparations. Agents blocking H2 receptors, used to inhibit gastric secretion in peptic ulcer, are usually called H.

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an·ti·his·ta·mine (nt-hst-mn, -mn)

n.

Any of several drugs used to counteract the physiological effects of histamine.

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anti·hista·mine adj.

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Antihistamine

A drug that inhibits the actions of histamine. Histamine causes dilatation of capillaries, contraction of smooth muscle, and stimulation of gastric acid secretion.

Mentioned in: Anti-Itch Drugs, Antinausea Drugs, Lichen Simplex Chronicus, Physical Allergy, Serum Sickness

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antihistamine

[-his′təmin]

Etymology: Gk, anti + histos, tissue, amine (ammonia compound)

any substance capable of reducing the physiologic and pharmacologic effects of histamine, including a wide variety of drugs that block histamine receptors. Many such drugs are readily available as over-the-counter medicines for the management of allergies. Toxicity resulting from the overuse of antihistamines and their accidental ingestion by children is common and sometimes fatal. These substances do not completely stop the release of histamine, and the ways in which they act on the central nervous system are not completely understood. The antihistamines are divided into histamine₁ (H₁) and histamine₂ (H₂) blockers, depending on the responses to histamine they prevent. H₁-blocking drugs, such as alkylamines, ethanolamines, ethylenediamines, and piperazines, are effective in the symptomatic treatment of acute allergies. Second-generation H₁ blockers, such as cetirizine, fexofenadine, and loratadine, cause less sedation. The H₂-blocking drugs are effective in the control of gastric secretions and are often used in the treatment of gastroesophageal reflux. Antihistamines can both stimulate and depress the central nervous system. antihistaminic, adj.

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antihistamine (an´tīhis´tmin),

n a drug that counteracts the release of histamine such as occurs in allergic reactions; also has topical anesthetic and sedative effects, as well as a drying effect on the nasal mucosa.

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antihistamine

a drug that counteracts the effects of histamine by acting on histamine receptors without activating them but preventing their accessibility to histamine. A competitive and reversible reaction. There are two types:

Those that block H₁ receptors are commonly referred to as the antihistamines and are widely used to relieve the symptoms of allergic reactions, especially urticaria. Some have an antinauseant action that is useful in the prevention of motion sickness and others have a sedative and hypnotic action.

H₂ receptor blocking agents inhibit the stimulation of gastric secretions.

See also histamine antagonists, H₂-receptor blocker.

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antihistamine 

Any substance that reduces the effect of histamine or blocks histamine receptors, usually the histamine 1 (H1) receptor. It is used in the treatment of allergic conjunctivitis and also in the temporary relief of minor allergic symptoms of the eye. Common agents include antazoline sulfate, azelastine hydrochloride, cetirizine, chlorphenamine, emedastine, epinastine hydrochloride, ketotifen, levocabastine, loratadine and olopatadine. See hypersensitivity; mast cell stabilizers.

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antihistamine

Antihistaminic Pharmacology An agent that counteracts the effects of histamine released during allergic reactions by blocking histamine–H₁ receptors Adverse effects Dry mouth, drowsiness, urine retention in ♂, tachycardia. See Histamine receptor.