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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 .
It contains fexofenadine, as the hydrochloride, an antihistamine; and pseudoephedrine, as the hydrochloride, a nasal decongestant. [ 2 ] In 2021, it was the 279th most commonly prescribed medication in the United States, with more than 800,000 prescriptions.
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.
There are four main types: H1, H2, H3, and H4. H1 receptors are linked to allergic responses, H2 to gastric acid regulation, H3 to neurotransmitter release modulation, and H4 to immune system function. There are four known histamine receptors: H 1 receptor H1 Receptors: These receptors are primarily located on smooth muscle cells, endothelial ...
react with or supply one mole of electrons in a redox reaction. [6] [7] The "hydrogen ion" and the "electron" in these examples are respectively called the "reaction units." By this definition, the number of equivalents of a given ion in a solution is equal to the number of moles of that ion multiplied by its valence.
The values below are standard apparent reduction potentials (E°') for electro-biochemical half-reactions measured at 25 °C, 1 atmosphere and a pH of 7 in aqueous solution. [ 1 ] [ 2 ] The actual physiological potential depends on the ratio of the reduced ( Red ) and oxidized ( Ox ) forms according to the Nernst equation and the thermal voltage .
Terfenadine acts as a peripherally-selective antihistamine, or antagonist of the histamine H 1 receptor. [3] It is a prodrug, generally completely metabolized to the active form fexofenadine in the liver by the enzyme cytochrome P450 3A4.
Quifenadine is a derivative of quinuclidylcarbinol, which reduces the effects of histamine on organs and systems. Quifenadine is a competitive blocker of H1 receptors. In addition, it activates the diamine oxidase enzyme, which breaks down about 30% of endogenous histamine.