Loratadine is a second-generation antihistamine with competitive antagonistic properties to peripheral histamine H1-receptors. Loratadine selectively inhibits H1-receptors primarily located on respiratory smooth muscle cells, vascular endothelial cells, the gastrointestinal tract, and immune cells. Loratidine is a competitive histamine antagonist that does not cross the blood-brain barrier. Therefore, it is non-sedative.
Loratadine binds to H1-receptors in different cells and causes a decrease in vascular permeability (prevents edema and flushing), decreases smooth muscle tone (bronchodilation), and decreases the activation of the peripheral nociceptive receptors (decreases pain and pruritus). At high concentrations, it can inhibit histamine release from mast cells and basophils, thereby reducing ICAM-1 expression in epithelial cells and inhibiting type 1 hypersensitivity reactions.