Antihistamine: Wikis


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A histamine antagonist is an agent that serves to inhibit the release or action of histamine. Antihistamine can be used to describe any histamine antagonist, but it is usually reserved for the classical antihistamines that act upon the H1 histamine receptor.

Antihistamines are used as treatment for allergies. Allergies are caused by an excessive response of the body to allergens, such as the pollen released by grasses and trees. An allergic reaction indicates an excessive release of histamines by the body. Other uses of antihistamines are to help with normal symptoms of insect stings even if there is no allergic reaction.

Contents

Clinical: H1- and H2-receptor antagonists

H1-receptor antagonists

In common use, the term antihistamine refers only to H1 antagonists, also known as H1 antihistamines. It has been discovered that these H1-antihistamines are actually inverse agonists at the histamine H1-receptor, rather than antagonists per se.[1] Clinically, H1 antagonists are used to treat allergic reactions.

Examples:

H2-receptor antagonists

H2 antagonists, like H1 antagonists, are also inverse agonists and not true antagonists. H2 histamine receptors are found principally in the parietal cells of the gastric mucosa. H2 antagonists are used to reduce the secretion of gastric acid, treating gastrointestinal conditions including peptic ulcers and gastroesophageal reflux disease.

Examples:

Experimental: H3- and H4-receptor antagonists

These are experimental agents and do not yet have a defined clinical use, although a number of drugs are currently in human trials. H3-antagonists have a stimulant and nootropic effect, and are being investigated for the treatment of conditions such as ADHD, Alzheimer's Disease, and schizophrenia, whereas H4-antagonists appear to have an immunomodulatory role and are being investigated as antiinflammatory and analgesic drugs.

H3-receptor antagonists

Examples:

H4-receptor antagonists

Examples:

Others

Inhibitors of histamine release

These agents (mast cell stabilizers) appear to stabilize the mast cells to prevent degranulation and mediator release. Although this is an unlikely method of action.

Examples:

Other agents with antihistaminergic activity

Many drugs, used for other indications, possess unwanted antihistaminergic activity.

Large doses of vitamin C are known to alleviate shock by inhibiting deaminizing proteins that release histamine.[2]

References

  1. ^ Leurs R, Church MK, Taglialatela M (2002). "H1-antihistamines: inverse agonism, anti-inflammatory actions and cardiac effects". Clin Exp Allergy 32 (4): 489–98. doi:10.1046/j.0954-7894.2002.01314.x. PMID 11972592.  
  2. ^ Klenner, Frederick R. Observations On the Dose and Administration of Ascorbic Acid.... Section "Ascorbic acid to the rescue."

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