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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.
When a person comes in contact with a specific trigger, their immune system produces antibodies called immunoglobulin E (IgE) molecules that bind to mast cells (immune cells found mainly in the skin, respiratory tract and digestive tract) and triggers the release of histamine and other chemicals that guards our immune system. [3]
Histamine release in the brain triggers secondary release of excitatory neurotransmitters such as glutamate and acetylcholine via stimulation of H 1 receptors in the cerebral cortex. Consequently, unlike the H 1 -antihistamines which are sedating, H 3 -antihistamines have stimulant and cognition-modulating effects.
Hydroxyzine works by blocking the effects of histamine. [9] It is a first-generation antihistamine in the piperazine family of chemicals. [ 8 ] [ 4 ] Common side effects include sleepiness , headache , and dry mouth .
Bilastine is an antihistamine medication used to treat hives (), allergic rhinitis and itchy inflamed eyes (allergic conjunctivitis) caused by an allergy. [6] It is a second-generation antihistamine and takes effect by selectively inhibiting the histamine H 1 receptor, preventing these allergic reactions. [7]
Histamine is a weak base (a compound able to react with a hydrogen ion to form an acid) that can link with acid groups within the granules of the mast cells. [8] The mechanism of the displacement theory. The crux of this theory lies in the assumption that histamine liberators release histamine by displacing it from cells.
They block mast cell degranulation, stabilizing the cell and thereby preventing the release of histamine and related mediators. One suspected pharmacodynamic mechanism is the blocking of IgE-regulated calcium channels. Without intracellular calcium, the histamine vesicles cannot fuse to the cell membrane and degranulate. [1]
Chloropyramine is known as a competitive reversible H 1 receptor antagonist (also known as an H 1 inverse agonist), meaning that it exerts its pharmacological action by competing with histamine for the H 1 subtype histamine receptor. By blocking the effects of histamine, the drug inhibits the vasodilation, increased vascular permeability, and ...