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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.
H 1-antihistamines work by binding to histamine H 1 receptors in mast cells, smooth muscle, and endothelium in the body as well as in the tuberomammillary nucleus in the brain. Antihistamines that target the histamine H 1-receptor are used to treat allergic reactions in the nose (e.g., itching, runny nose, and
H 1-receptor antagonists are competitive inhibitor of histamine receptor H 1 and are used to treat allergies. This group is often referred simply as antihistamines . Wikimedia Commons has media related to H1 receptor antagonists .
In addition, subjective sleepiness correlated well with the brain H 1 receptor occupancy. [45] PET studies with antihistamines have found that brain H 1 receptor occupancy of more than 50% is associated with a high prevalence of somnolence and cognitive decline , whereas brain H 1 receptor occupancy of less than 20% is considered to be non ...
The H 1 receptor is a histamine receptor belonging to the family of rhodopsin-like G-protein-coupled receptors. This receptor is activated by the biogenic amine histamine . It is expressed in smooth muscles , on vascular endothelial cells , in the heart, and in the central nervous system .
It also crosses the blood–brain barrier and inversely agonizes the H 1 receptors centrally. [70] Its effects on central H 1 receptors cause drowsiness. Diphenhydramine is a potent antimuscarinic (a competitive antagonist of muscarinic acetylcholine receptors) and, as such, at high doses can cause anticholinergic syndrome. [71]
Mirtazapine is a very strong H 1 receptor antagonist and, as a result, it can cause powerful sedative and hypnotic effects. [11] A single 15 mg dose of mirtazapine to healthy volunteers has been found to result in over 80% occupancy of the H 1 receptor and to induce intense sleepiness. [92]
Fexofenadine, sold under the brand name Allegra among others, [10] is an antihistamine pharmaceutical drug used in the treatment of allergy symptoms, such as hay fever and urticaria. [11] Therapeutically, fexofenadine is a selective peripheral H 1 blocker.