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Related to antihistamine: decongestant


(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 ?
Lastly, it should be noted that patients can prefer different antihistamine eye drops despite their overall ocular discomfort, (30,33) with the differences in acceptability likely to be due to the pH of the eye drops.
Meta-analyses show that oral antihistamines are not more effective than intranasal corticosteroids for eye symptoms.
Yanai categorizes antihistamines into three classes: fexofenadine, which does not cross the blood-brain barrier even at supratherapeutic doses; the "less sedating" antihistamines, which occupy roughly 20% or less of available cortical [H.
14) Thus, when prescribing an antihistamine for individuals with SAR, all attributes of an antihistamine should be assessed to prescribe an agent that provides maximum clinical benefit, without interfering with daily living and working activities.
We are very excited about our new licensing relationship with Sepracor in the United States and the prospect of expanding our antihistamine business," stated Roch Doliveux, CEO of UCB.
There are some new antihistamines which are very effective, good ones if you are going away on holiday, some which you just need to take once a day.
For those really bad days, when your sinuses are feeling the pressure, use an antihistamine that also features a decongestant for sinus control.
We expected that patients who received either the antihistamine or corticosteroid, in addition to the antibiotic, would have clearing symptoms and less recurrence," said Chonmaitree.
Until last year, many allergy sufferers would have reached for a medication called Claritin, a newer generation of antihistamine that doesn't make users drowsy.
Many health plans have put other antihistamine prescription allergy drugs on higher, more expensive pharmacy tiers to discourage members from choosing the prescription medications over Claritin.
You're allergic," he told her, and prescribed a steroidal nose spray and a prescription antihistamine.