Antihistamines

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

The H1-antagonists are distinguished:

• Sedating H1 antagonists (1st generation):
  • Clemastine
  • Dexchloropheniramine
  • Dimetinden
  • Hydroxycin
  • Ketotifen
  • Meclizine
  • Promethazine and others
• Non-sedating H1 antagonists (2nd generation):
  • Azelastine
  • Cetirizine
  • Desloratadine
  • Ebastine
  • Fexofenadine
  • Levocetirizine
  • Loratadine
  • Mequitazine
  • Mizolastine
  • Terfenadine
  • Rupatadine.

Competitive inhibition of H1 receptors, diaminooxidase inhibition, inhibition of potassium leakage from the cells. 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 are inhibited. The spectrum of action of H1 antihistamines thus includes anti-allergic and antiphlogistic effects.

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.

• 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.

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