Oral and topical antihistamines: pharmacologic properties and therapeutic potential in ocular allergic disease

Allergic eye disease is a common clinical occurrence in individuals who experience local and systemic hypersensitivity reactions. The majority of ocular symptoms involve the conjunctiva and lids, which are exposed to the environment and thereby are sites of interaction between allergens and immunocompetent cells. Signs and symptoms of ocular involvement can manifest as itching, chemosis, tearing, swollen lids, and photophobia.

Histamine is a key preformed mediator released when allergen molecules crosslink to antigen-binding components of adjacent IgE molecules on mast cells or basophil surface. On its release, histamine acts on H1-receptors on a variety of tissues and cells, including blood vessels, smooth muscle, and sensory nerves.

Drugs classified as H1-receptor antagonists, commonly referred to as the antihistamines, are among the most efficacious and frequently used medications for ocular and systemic allergy symptoms.

This review focuses on the pharmacologic actions and side effects of oral first-generation sedating or classic H1-receptor antagonists; the second-generation, relatively nonsedating H1-receptor antagonists; and the topical ocular antihistamine/decongestants and single-entity antihistamine formulations.