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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 ?
The doctor or the nurse is trained to evaluate and decide if the child's condition can be managed by an anti-histamine pill or he requires an Epi Pen jab.
Doctors and nurses in both the hospitals were trained for a day on the selection of cases, 20MWBC test, the dose, the use of ASV and the use of adrenaline and anti-histamines following a standard protocol.
gt;> Have a first aid kit at home, handy in the car or in your luggage if you're traveling and include emergency items like plasters, antiseptic wipes for cleaning cuts and grazes and anti-histamines .
And despite guidelines advocating the use of widely available non-sedating treatment, 28 per cent of the students taking medication were on a sedating anti-histamine, findings showed.
Now you have it, it can't really be cured but you can treat it with over-the-counter anti-histamine tablets and sprays.
Dutch researchers say onion skins contain quercetin,a potent natural anti-histamine and anti-inflammatory shown to help hay fever sufferers.
Dutch researchers say onion skins contain quercetin, a potent natural anti-histamine and anti-inflammatory shown to help hay fever sufferers.
The same prescriptions which probably patients have been immune to for a number of years, such as anti-histamine tablets and some antibiotics, even, which have been dolled out like Smarties.
Vitamin C is thought to have natural anti-histamine effects, so include berries, kiwi fruit, peppers, tomatoes, broccoli, red onions, citrus fruit, berries and apples.
Thalidomide was first created in West Germany by a drug company which was unsuccessfully attempting to develop an anti-histamine when they noticed the drug acted as an effective tranquilliser and painkiller.
Paramedics spent an hour treating cabbie James with anti-histamine in the back of the ambulance.
This figure rises to 70% if they are taking a sedating anti-histamine treatment, which can cause drowsiness.