Deficiency of C1 Inhibitor leads to unopposed activation of complement, with 
localized, unpredictable, and sometimes life-threatening attacks of angioedema. 
Treatment with plasma-derived C1 Inhibitor rapidly aborts attacks, and may be 
lifesaving, but is expensive, requires use of a pooled blood product, may need 
to be repeated and may not be effective in autoantibody mediated angioedema. The 
antifibrinolytic agents aprotinin, tranexamic acid, and epsilon-aminocaproic 
acid are useful for prophylaxis and treatment of angioedema, likely by 
inhibiting plasmin. Specific drugs to replace the deficient C1 Inh have not been 
reported. The kallikrein inhibitor DX-88 (Dyax) has received orphan drug status 
in Europe and is undergoing clinical trial in Europe and the USA.