An H 3-antihistamine is a classification of drugs used to inhibit the action of histamine at the H 3 receptor.H 3 receptors are primarily found in the brain and are inhibitory autoreceptors located on histaminergic nerve terminals, which modulate the release of histamine.
- Medical uses
Histamine produces increased vascular permeability, causing...
H1-antihistamines refer to compounds that inhibit the...
- Atypical antihistamines
Inhibit the action of histidine decarboxylase: 1....
- Medical uses
Pages in category "Antihistamines" The following 36 pages are in this category, out of 36 total. This list may not reflect recent changes ().
H 1 antagonists, also called H 1 blockers, are a class of medications that block the action of histamine at the H 1 receptor, helping to relieve allergic reactions.Agents where the main therapeutic effect is mediated by negative modulation of histamine receptors are termed antihistamines; other agents may have antihistaminergic action but are not true antihistamines.
Although histamine is small compared to other biological molecules (containing only 17 atoms), it plays an important role in the body. It is known to be involved in 23 different physiological functions. Histamine is known to be involved in many physiological functions because of its chemical properties that allow it to be versatile in binding.
- 111.148 g·mol−1
- 83.5 °C (182.3 °F; 356.6 K)
- Easily soluble in cold water, hot water
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Sep 29, 2019 · Perhaps the most striking method of demonstrating the effect of antihistamine substances is to use them to protect guinea-pigs against the action of histamine sprayed into the air from an atomizer.
Cetirizine, sold under the brand name Zyrtec among others, is a second generation antihistamine used to treat allergic rhinitis (hay fever), dermatitis, and urticaria. It is taken orally.  Effects generally begin within an hour and last for about a day. 
Diphenhydramine is an antihistamine mainly used to treat allergies. It can also be used for insomnia, symptoms of the common cold, tremor in parkinsonism, and nausea. It is used by mouth, injection into a vein, injection into a muscle, or applied to the skin.
Loratadine, sold under the brand name Claritin among others, is a medication used to treat allergies. This includes allergic rhinitis (hay fever) and hives. It is also available in combination with pseudoephedrine, a decongestant, known as loratadine/pseudoephedrine.
Antihistamines provide their primary action by blocking histamine H 1 at the receptor site. They have no effect on rate of histamine release, nor do they inactivate histamine. By inhibiting the activity of histamine, they can reduce capillary fragility, which produces the erythema, or redness, associated with allergic reactions.
Feb 05, 2019 · Antihistamines are a class of agents that block histamine release from histamine-1 receptors and are mostly used to treat allergies or cold and flu symptoms, although some first-generation antihistamines may also be used for other conditions.