In the Literature

Helgeson ME, Pigott AM, Kierski KR. Retrospective review of diphenhydramine versus diphenhydramine plus glucocorticoid for treatment of uncomplicated allergic reaction in dogs. J Vet Emerg Crit Care (San Antonio). 2021;31(3):380-386.

The Research …

According to this study, ≈1.2% of emergency veterinary visits are for mild allergic reactions. Type I hypersensitivity reactions occur when immunoglobulin E antibodies on the surface of mast cells and basophils (formed during initial exposure to an allergen) crosslink and trigger degranulation after re-exposure to the allergen. Exposure can occur via direct contact with or ingestion, inhalation, or injection of an allergen. Mast cell and basophil degranulation releases histamine, leukotrienes, and prostaglandins. Histamine activates H₁ receptors on the endothelium, vascular smooth muscle, hepatocytes, and lymphocytes.