“May all be happy, may all be healed, may all be at peace and may no one ever suffer."
Azelastine, a phthalazinone derivative, exhibits histamine H1 receptor antagonist activity in isolated tissues, animal models and humans. It is administered as a racemic mixture with no difference in pharmacologic activity noted between the enantiomers in invitro studies. The major metabolite, desmethylazelastine, also possesses H1-receptor antagonist activity.