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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.
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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 ?
* On March 15, 2019, we announced that we had we entered into an exclusive license agreement with Ocumension Therapeutics for the development and commercialization of Nicox's product ZERVIATE (cetirizine ophthalmic solution), 0.24% for the treatment of allergic conjunctivitis for the Chinese market.
Participants started taking cetirizine (10mg) orally daily and continued for one year, in addition to their established NMOSD disease-modifying therapy.
Mattila and Paakaari [6] reported in their study of newer non-sedating antihistamines fexofenadine, loratadine, acrivastine, astemizole, cetirizine, astemizole and terfenadine however not entirely free from central effects and there at astemizole quantitative differences between them psychomotor and sleep studies in the healthy subjects in laboratory may predict that antihistamine does not cause drowsiness; but the safety margin is narrow enough to cause a central sedating effect during actual treatment.
In this case, the Chinese medicine dose group, high-dose group, and the Western cetirizine group are significantly different (P < 0.001).
He required cetirizine occasionally (1-2 times a week).
8,829,005 includes method of treatment claims that cover the company's cetirizine product candidate (cetirizine ophthalmic solution, 0.24 percent).
Various gel formulations of cetirizine HCl were prepared and optimized by using response surface methodology containing different ratios of PG(X1) and PEG(X2) taken as two independent variables whereas cumulative amount of cetirizine HCl was used to calculate dependent (response) variables (Y1 - Y7).
A small amount of cetirizine HCl was dissolved in 10 ml of distilled water in separating funnel, shaked it for 10 min, added 10 ml of octanol and shaked vigorously for 10 min.
Just recently, Food and Drug Administration (FDA) associated cetirizine with potential signs of severe risk for oculogyric crisis.2 A retrospective study has established that cetirizine causes oculogyric complications particularly in the paediatric population (8 paediatric cases out of a total of 9 cases) with dosage extending from 5 to 10mg and commencement of symptoms varying from 3 to 184 days.3 Confirmed rechallenge data were seen in 6 cases of oculogyric crisis while 8 cases underwent thorough neurologic consultation with radiographic proceedings.
In the study, 422 people with seasonal allergies received 12 treatments of cetirizine (Zyrtec) alone, with acupuncture, or with sham (fake) acupuncture over eight weeks.
These agents are used for allergic rhinitis, sinusitis, seasonal allergic rhinitis, and chronic idiopathic urticaria, The three OTC agents in this class also can be divided into two subgroups: piperazines (cetirizine) and piperidines (fexofenadine and loratadine).
Cetirizine is used for seasonal allergic rhinitis in children aged 2-6 years (6).