Inhibition by azelastine of the immunologically induced histamine release from isolated guinea pig mast cells.

4-(p-Chlorobenzyl)-2-(hexahydro-1-methyl-1H-azepin-4-yl)-1-(2H)-phthalazinone (azelastine, A 5610) did not affect the spontaneous histamine release but inhibited effectively the allergic histamine release from isolated mesenteric mast cells of actively sensitized guinea pigs. At 10(-6) mol/l concentration the inhibition was almost equal to that caused by adrenaline (10(-8) mol/l).