Histamine antagonist

A histamine antagonist is an agent which serves to inhibit the release or action of histamine.

Although the term "antihistamine" could technically be used for any histamine antagonist, in practice the term is reserved for the classical antihistamines which act upon the H1 histamine receptor.

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Clinical: H₁- and H₂-receptor antagonists

H₁-receptor antagonists

Main article: H1 antihistamine

In common use, the term antihistamine refers only to H₁-receptor 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]

H₂-receptor antagonists

Main article: H₂-receptor antagonist

Clinically-relevant histamine H₂-receptors are found principally in the parietal cells of the gastric mucosa. H₂-receptor "antagonists" are also inverse agonists, rather than true antagonists; and are used to reduce the secretion of gastric acid. Examples include cimetidine, ranitidine, and famotidine.

Experimental: H₃- and H₄-receptor antagonists

These are experimental agents and do not yet have a defined clinical use.

H₃-receptor antagonists

• ABT-239
• Thioperamide
• Clobenpropit
• Impromidine
  • • Similar in structure to burimamide
    • Imidazole ring
    • Polar moiety on the side chain - thiourea, isothiourea and guanidine
    • other substituents are highly variable

H₄-receptor antagonists

• Thioperamide

Others

Inhibitors of histamine release

These agents (mast cell stabilizers) appear to stabilise the mast cells to prevent degranulation and mediator release.

• Cromoglicate (cromolyn)
• Nedocromil

Other agents with antihistaminergic activity

Many drugs, used for other indications, possess unwanted antihistaminergic activity. These include tricyclic antidepressants, antipsychotics, etc.

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. PMID 11972592.