Author: Prof. Dr. med. Peter Altmeyer

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Last updated on: 27.09.2023

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H1 antagonists; Histamine receptor antagonists

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Substances that attenuate or abolish the effects of histamine by reversible binding to histamine receptors.

A distinction is made among the H1 antagonists:

Pharmacodynamics (Effect)
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Competitive inhibition ofH1 receptors, diaminooxydase inhibition, inhibition of potassium leakage from cells. Inhibition of histamine-mediated effects such as vasodilation, increased vascular permeability via inhibition of the release of proinflammatory cytokines such as IL-4, IL-6, Il-8,IL-13 from mast cells and the expression of the adhesion molecule P-selectin from endothelial cells. The spectrum of action of H1 antihistamines thus includes antiallergic and antiphlogistic effects.

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  • urticaria
  • allergic rhinitis and conjunctivitis
  • drug allergies
  • insect bites
  • Quincke's edema
  • pruritus
  • Serum sickness

Some agents in this drug group have more sedative properties, so they are used as sleeping pills. Diphenhydramine or doxylamine are examples.

Agents that have a stronger anticholinergic effect, such as diphenhydramine and dimenhydrinate (8-chlorotheophylline salt of diphenhydramine), are used as antiemetics for kinetosis.

Undesirable effects
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Sedation (inability to drive! with the H1 antagonists), dry mouth (due to anticholinergic effect), gastrointestinal disorders, central nervous disorders. The photosensitizing potency of the newer non-sedating antihistamines is not proven.

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Central steaming pharmaceuticals, alcohol (effect intensification).

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Pregnancy, infants, bladder neck adenoma.

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Before starting antihistaminergic therapy, it is recommended that all patients undergo a risk assessment according to the CONGA report (acronym for Consensus Group on New-Generation Antihistamines):
  • Does any form of heart disease already exist? If so, an antihistamine with little or no interaction with the cardiac potassium channels should be chosen.
  • Is there a co-medication with the following preparations: macrolides, opiates, imidazoles, psychotropic drugs, anti-malaria drugs? If so, an accurate re-evaluation of the medication should be carried out and the combination of QT time prolonging preparations should be done carefully and only if strictly indicated.
  • Are there other risk factors such as liver diseases, electrolyte shifts, special potassium-rich diets? If so, treatment of the underlying diseases and strict indication for the prescription of the antihistamine.

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  • Netzwerk aktuell (2006) Photosensitization through antihistimanics. Medication telegram 37: 60


Last updated on: 27.09.2023