XX is an oral non-sedating H 1-blocker that is similar in structure to cyproheptadine and azatadine, other H 1-blockers. It differs structurally from the other non-sedating HÀ-blockers terfenadine and astemizole. Due to poor penetration into the CNS and a low affinity for CNS H 1-receptors, CNS effects are less with it compared to the traditional H 1-blockers. It was approved by the FDA in April 1993 to relieve symptoms associated with seasonal allergic rhinitis. The mechanism of action is similar to other H1-blockers, it does not prevent the release of histamine but competes with free histamine for binding at the H1-receptor. This competitive antagonism blocks the effects of histamine on H1-receptors in the GI tract, uterus, large blood vessels, and bronchial muscle. It does not readily cross the blood-brain barrier, and it preferentially binds at H1-receptors in the periphery rather than within the brain, which probably accounts for some of its nonsedating character. |