Effects of a plasma-derived C1 esterase inhibitor on hemostatic activation, clot formation, and thrombin generation

Hereditary angioedema (HAE) is a rare, autosomal dominant disease in which C1 esterase inhibitor (C1 INH) is deficient or dysfunctional. Package inserts for nanofiltered C1 esterase inhibitor (C1 INH-nf) products contain warnings about thrombotic events. The objective of this study was to evaluate the effect of C1 INH-nf on hemostatic activation, clot formation, and thrombin generation. Ten healthy volunteers provided blood samples for thromboelastometry using the ROTEM system. Platelet-poor samples were prepared for thrombin generation studies. C1 INH-nf was added to samples at final concentrations of 0.14, 0.7, 1.4, 2.8, and 7.0 U/ml. Recombinant factor VIIa and prothrombin complex concentrate were used as procoagulant controls, and antithrombin and desirudin were used as anticoagulant controls. C1 INH-nf had no procoagulant effect on hemostasis based on thromboelastometry, regardless of the final concentration or activating reagent used (P > 0.05 for all comparisons of C1 INH-nf versus negative control). C1 INH-nf 2.8 and 7.0 U/ml concentrations had a statistically significant anticoagulant effect on maximum clot firmness (P < 0.05 for all comparisons of C1 INH-nf versus negative control), with a magnitude similar to that observed with desirudin. C1 INH-nf had no effect on thrombin generation lag time, peak thrombin generation, or thrombin generation rate, regardless of the final concentration or activating reagent used (P < 0.05 for all comparisons of C1 INH-nf versus negative controls). We found no evidence of a procoagulant effect of C1 INH-nf when studied ex vivo at concentrations up to 10-fold higher than those achieved with clinical dosing in patients with HAE.