ICATIBANT IS A COMPETITIVE ANTAGONIST SELECTIVE FOR THE BRADYKININ B2 RECEPTOR, WITH AN AFFINITY SIMILAR TO BRADYKININ. HEREDITARY ANGIOEDEMA IS CAUSED BY AN ABSENCE OR DYSFUNCTION OF C1-ESTERASE-INHIBITOR, A KEY REGULATOR OF THE FACTOR XII/KALLIKREIN PROTEOLYTIC CASCADE THAT LEADS TO BRADYKININ PRODUCTION. BRADYKININ IS A VASODILATOR WHICH IS THOUGHT TO BE RESPONSIBLE FOR THE CHARACTERISTIC HAE SYMPTOMS OF LOCALIZED SWELLING, INFLAMMATION, AND PAIN. ICATIBANT INHIBITS BRADYKININ FROM BINDING THE B2 RECEPTOR AND THEREBY TREATS THE CLINICAL SYMPTOMS OF AN ACUTE, EPISODIC ATTACK OF HAE.