Ecallantide is a potent and selective human plasma kallikrein inhibitor that is indicated for the symptomatic treatment of hereditary angioedema. Ecallantide is a recombinant 60-amino-acid protein produced in Pichia pastoris yeast cells that contains three intramolecular disulfide bonds. Ecallantide works by blocking kallikrein to participate in the kallikrein-kinin system, which is a complex proteolytic cascade that initiates inflammatory and coagulation pathways.