Definition of "Antihistamine"

Last modified: 5 days



Antihistamine (aka histamine antagonist) inhibits the action of histamine, used to relieve allergies.

Classification
  • Histamine H1-receptor antagonist, used to Tx allergic reactions in the nose (e.g. itching, runny nose, and sneezing), which are used off-label for insomnia. They are also used to Tx motion sickness or vertigo caused by problems w/ the inner ear, by binding to H1 receptors in mast cells, smooth muscle, and endothelium in the body and tuberomamillary nucleus in the brain. Examples include:
    • 3rd generation antihistamine, as it is less able to pass the BBB and cause sedation:
      • Fexofenadine (Allegra, Telfast)
    • 2nd generation antihistamines, as they are less able to cross the BBB and thus have diminished effects on the CNS, thus less likely to induce drowsiness or interfere w/ memory formation:
      • Cetirizine (Zyrtec)
      • Loratadine (Claritin)
    • 1st generation antihistamines:
      • Quetiapine (an antipsychotic, Seroquel)
      • Doxylamine (Unisom)
      • Diphenhydramine (Benadryl)
  • Histamine H2-receptor antagonist, used to Tx gastric acid conditions (e.g. peptic ulcers and acid reflux), by binding to H2 receptors in the upper GI tract, primarily in the stomach
See also
  • H2 blocker

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Definition of Antihistamine | Autoprac


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