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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 ...
Therapeutically, fexofenadine is a selective peripheral H 1 blocker. It is classified as a second-generation antihistamine because it is less able to pass the blood–brain barrier and cause sedation, compared to first-generation antihistamines. [12] [13] It was patented in 1979 and came into medical use in 1996. [14]
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 .
The first H 1 receptor antagonists were discovered in the 1930s and were marketed in the 1940s. [22] Piperoxan was discovered in 1933 and was the first compound with antihistamine effects to be identified. [ 22 ]
Clemastine, also known as meclastin, is a first-generation H1 histamine antagonist (antihistamine) with anticholinergic properties (drying) and sedative side effects. [1] Like all first-generation antihistamines, it is sedating. [2] [3] Patented in 1960, it came into medical use in 1967. [4]
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 .
Cetirizine acts as a highly selective antagonist of the histamine H 1 receptor. [3] The K i values for the H 1 receptor are approximately 6 nM for cetirizine, 3 nM for levocetirizine, and 100 nM for dextrocetirizine, indicating that the levorotatory enantiomer is the main active form. [3]
Cyproheptadine is a very potent antihistamine or inverse agonist of the H 1 receptor. At higher concentrations, it also has anticholinergic, antiserotonergic, and antidopaminergic activities. Of the serotonin receptors, it is an especially potent antagonist of the 5-HT 2 receptors.