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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.
The histamine receptors are a class of G protein–coupled receptors which bind histamine as their primary endogenous ligand. [1] [2] Histamine receptors are proteins that bind with histamine, a neurotransmitter involved in various physiological processes. There are four main types: H1, H2, H3, and H4.
It is a first-generation antihistamine and works by blocking the histamine H 1 receptor. [2] Common side effects include sleepiness, restlessness, and weakness. Other side effects may include dry mouth and wheeziness. [2] Chlorpheniramine was patented in 1948 and came into medical use in 1949. [3] It is available as a generic medication and ...
Doxylamine and other first-generation antihistamines are the most widely used sleep medications in the world. [6] Typical side effects of doxylamine (at recommended doses) include dizziness, drowsiness, grogginess, and dry mouth, among others. [7] [4] As an antihistamine, doxylamine is an inverse agonist of the histamine H 1 receptor.
Histamine H 1 receptors are activated by endogenous histamine, which is released by neurons that have their cell bodies in the tuberomammillary nucleus of the hypothalamus. The histaminergic neurons of the tuberomammillary nucleus become active during the 'wake' cycle, firing at approximately 2 Hz; during slow wave sleep , this firing rate ...
Use in pregnancy appears safe but has not been well studied and use when breastfeeding is of unclear safety. [5] It is classified as a second-generation antihistamine and works by blocking histamine H 1-receptors. [6] [3] Levocetirizine was approved for medical use in the United States in 2007, [3] and is available as a generic medication. [4]
Another type of antihistamines known as H2-antihistamines are used to treat gastrointestinal conditions caused by excessive stomach acid. [8] Mechanism. H-1 antihistamines work by inhibiting histamine from binding to H-1 receptors. Histamine receptors expressed in smooth muscles, vascular endothelial cells, the heart, and the central nervous ...
Diphenhydramine, sold under the brand name Benadryl among others, is an antihistamine and sedative. It is a first-generation H 1-antihistamine and it works by blocking certain effects of histamine, which produces its antihistamine and sedative effects. [11] [2] Diphenhydramine is also a potent anticholinergic. [12]