H1 receptor antagonists' allergy treatment foundation — the antihistamine drug class blocking histamine H1 receptors to relieve allergic rhinitis, urticaria, and other histamine-mediated allergic symptoms, spanning both older first-generation agents (diphenhydramine, chlorpheniramine) and newer second-generation formulations (cetirizine, loratadine, fexofenadine) — represents one of...