Histamine antagonist

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A histamine antagonist is an agent which 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.

Many people suffer from allergies. These are caused by an excessive response of the body to allergens, materials that are sometimes omnipresent, such as the pollen released by grasses and trees. An allergic reaction indicates an excessive release, by the body, of histamines. The antihistamines described here inhibit the release of these histamines, thus relieving the allergic reactions and symptoms.

Contents 1 Clinical: H1- and H2-receptor antagonists 1.1 H1-receptor antagonists 1.2 H2-receptor antagonists 2 Experimental: H3- and H4-receptor antagonists 2.1 H3-receptor antagonists 2.2 H4-receptor antagonists 3 Others 3.1 Inhibitors of histamine release 3.2 Other agents with antihistaminergic activity 4 References 5 External links

[edit] Clinical: H₁- and H₂-receptor antagonists

[edit] H₁-receptor antagonists

Main article: H₁ antagonist

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:

• Diphenhydramine
• Loratadine
• Desloratadine
• Meclizine
• Quetiapine
• Fexofenadine

[edit] H₂-receptor antagonists

Main article: H₂ antagonist

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:

• Cimetidine
• Famotidine
• Ranitidine

[edit] Experimental: H₃- and H₄-receptor antagonists

These are experimental agents and do not yet have a defined clinical use. H₃-antagonists have a stimulant effect, and are being investigated for the treatment of conditions such as ADHD, Alzheimer's Disease and schizophrenia, while H₄-antagonists appear to have an immunomodulatory role.

[edit] H₃-receptor antagonists

Examples:

• ABT-239
• Cipralisant
• Ciproxifan
• Clobenpropit
• Thioperamide

[edit] H₄-receptor antagonists

Examples:

• Thioperamide

[edit] Others

[edit] Inhibitors of histamine release

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

Examples:

• Cromoglicate (cromolyn)
• Nedocromil

[edit] Other agents with antihistaminergic activity

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

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

[edit] References

[edit] External links

• MeSH Histamine+antagonist

v • d • e Antihistamines (primarily R06) Aminoalkyl ethers Bromazine/Bromodiphenhydramine • Carbinoxamine • Clemastine • Chlorphenoxamine • Diphenylpyraline • Diphenhydramine • Doxylamine • Orphenadrine • Phenyltoloxamine Substituted alkylamines Brompheniramine • Chlorphenamine • Dexbrompheniramine • Dexchlorpheniramine • Dimetindene • Pheniramine • Talastine Substituted ethylenediamines Chloropyramine • Histapyrrodine • Mepyramine • Methapyrilene • Tripelennamine (Pyribenzamine) Phenothiazine derivatives Alimemazine • Hydroxyethylpromethazine • Isothipendyl • Mequitazine • Methdilazine • Oxomemazine • Promethazine Piperazine derivatives Buclizine • Cetirizine • Chlorcyclizine • Cinnarizine • Cyclizine • Hydroxyzine • Levocetirizine • Meclizine • Niaprazine • Oxatomide Others for systemic use Antazoline • Azatadine • Bamipine • Cyproheptadine • Deptropine • Dimebon • Ebastine • Epinastine • Ketotifen • Mebhydrolin • Mizolastine • Phenindamine • Pimethixene • Pyrrobutamine • Rupatadine • Triprolidine • selective (Acrivastine • Astemizole • Azelastine • Desloratadine • Fexofenadine • Loratadine • Terfenadine) For topical use Bamipine • Chloropyramine • Chlorphenoxamine • Clemastine • Dimetindene • Diphenhydramine • Isothipendyl • Mepyramine • Promethazine • Thenalidine Antiallergic agents excluding corticosteroids Antazoline • Azelastine Other antiallergics Emedastine • Epinastine • Ketotifen • Montelukast • Olopatadine

v • d • e Receptor agonists, antagonists, and reuptake inhibitors BA/M: 5-HT (serotonin) receptor Serotonin receptor agonist • Serotonin antagonist (5-HT3) • Serotonin uptake inhibitor (SSRI) BA/M: Dopamine receptor Dopamine agonist • Dopamine antagonist • Dopamine reuptake inhibitor BA/M: Adrenergic receptor Adrenergic agonist (Alpha, Beta2) • Adrenergic antagonist (Alpha, Beta) • Adrenergic uptake inhibitor BA/M: Histamine receptor Histamine agonist • Histamine antagonist (H1, H2) Acetylcholine receptor Cholinergic (Muscarinic, Nicotinic) • Anticholinergic (Muscarinic, Nicotinic) • Acetylcholinesterase inhibitor AA: GABA receptor GABA agonist • GABA antagonist AA: Glutamate receptor NMDA receptor (NMDA receptor antagonist)