Three medications are available for acute treatment of HAE: Berinert-P® (plasma-derived C1 esterase inhibitor, approved in the US and Europe), KALBITOR® (ecallantide, a kallikrein inhibitor, approved only in the US currently), and Firazyr® (icatibant, bradykinin β2-receptor inhibitor, approved only in Europe currently). Here, C1S is linked to hereditary angioedema.