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Antihistamine Drugs: Mechanisms, Clinical Applications, and Therapeutic Significance in Modern Medicine
Antihistamine drugs are a class of pharmaceutical agents that inhibit the biological effects of histamine, a naturally occurring chemical mediator involved in various physiological processes, including allergic reactions, gastric acid secretion, neurotransmission, and immune responses
Histamine is released by mast cells, basophils, and certain neurons in response to allergens, tissue injury, or immune triggers, leading to symptoms such as itching, swelling, nasal congestion, hives, and bronchoconstriction. Antihistamines act by blocking histamine receptors and are widely used to manage allergic disorders, gastrointestinal conditions, and other histamine-mediated pathologies.
Types of Histamine Receptors and Drug Classification
Histamine exerts its effects through four known receptor subtypes: H1, H2, H3, and H4, each mediating distinct physiological responses:
H1 Receptors: Found in smooth muscles, endothelium, and the central nervous system, H1 receptors are responsible for allergic responses, vasodilation, increased vascular permeability, and bronchoconstriction. H1-antihistamines, such as loratadine, cetirizine, diphenhydramine, and fexofenadine, are primarily used to treat allergic…