Recombinant activated factor VII effectively reverses the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin ex vivo as measured using thromboelastography.

Bleeding is the major adverse reaction to anticoagulants, leading to significant morbidity and even mortality. Protamine is a specific antidote for heparin yet is only partially effective for enoxaparin, and the activated factor X inhibitor fondaparinux and the direct thrombin inhibitors argatroban and bivalirudin lack specific antidotes. We evaluated the ability of recombinant activated factor VII (rFVIIa), a general hemostatic agent, to reverse the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin, as measured by thromboelastography. Whole-blood samples containing each test anticoagulant, with or without rFVIIa 1.5-4.5 microg/ml, were prepared ex vivo (n >or= 48, each anticoagulant) and analyzed by thromboelastography. The thromboelastography parameters of clot initiation, propagation, rigidity and elasticity were compared for the ex-vivo samples for each anticoagulant. The reversal ability of rFVIIa was also assessed using the standard clinical assay used to monitor each anticoagulant. Thromboelastography was performed on blood from eight stably anticoagulated patients, with and without exogenous rFVIIa. For each anticoagulant, rFVIIa significantly improved and, in some cases, completely normalized all thromboelastography parameters (P < 0.001). rFVIIa significantly (P < 0.01) decreased the activated partial thromboplastin time for argatroban-containing, bivalirudin-containing, or heparin-containing blood yet did not affect the anti-activated factor X levels for enoxaparin-containing or fondaparinux-containing blood. By thromboelastography, rFVIIa exerted generally similar reversal effects on the anticoagulated patient samples as on the ex-vivo samples. In conclusion, rFVIIa effectively reverses the anticoagulant effects of heparin, enoxaparin, fondaparinux, argatroban, and bivalirudin, and should be considered for patients with excessive bleeding associated with these anticoagulants.

Differential effects of direct thrombin inhibitors and antithrombin-dependent anticoagulants on the dynamics of clot formation.

New anticoagulants, including the direct thrombin inhibitors (DTIs) and fondaparinux, are increasingly replacing unfractionated heparin and enoxaparin. We examined the effects of argatroban (n = 60), bivalirudin (n = 44), heparin (n = 14), enoxaparin (n = 22), and fondaparinux (n = 24) on clot formation utilizing thromboelastography. Blood samples containing anticoagulants at clinically relevant concentrations were prepared ex vivo and analyzed using kaolin or tissue factor activation. Thromboelastography parameters of clot initiation (R), clot propagation (K and angle), clot rigidity (maximum amplitude) and clot elasticity (G) were compared between anticoagulants. Thromboelastography was also performed on blood from eight patients receiving anticoagulants. Each anticoagulant exerted significant concentration-dependent effects on R, K and angle. Only heparin, enoxaparin, and fondaparinux significantly affected maximum amplitude and G. Significant differences existed for all parameters between heparin and each anticoagulant and between fondaparinux and each DTI (P < 0.001), and for angle, maximum amplitude, and G between enoxaparin and each DTI (P < 0.008). Thromboelastography responses in ex-vivo samples and patient samples were comparable. In conclusion, whereas argatroban, bivalirudin, heparin, enoxaparin and fondaparinux each delay clot formation, the DTIs do not alter clot rigidity or elasticity. The reduced bleeding reported with DTIs versus heparin may relate to the fact that clots form with normal rigidity and elasticity.

Safety and pharmacokinetics of recombinant factor XIII-A2 administration in patients with congenital factor XIII deficiency.

Congenital factor XIII (FXIII) deficiency is associated with a tendency for severe bleeding, a risk for spontaneous abortion, and a high rate of spontaneous intracranial hemorrhage. This phase 1 escalating-dose study was developed to evaluate the safety and pharmacokinetics of a single administration of human recombinant FXIII-A2 (rFXIII-A2) homodimer in adults with congenital FXIII deficiency. Pharmacokinetics and activity of rXIII and changes in endogenous B subunit levels were assessed. Recombinant FXIII-A2 homodimer were complexed with endogenous FXIII-B subunits to form an FXIII-A2B2 heterotetramer with a half-life of 8.5 days, similar to that of endogenous FXIII. The median dose response was a 2.4% increase in FXIII activity based on unit per kilogram rFXIII administered. After the administration of rFXIII-A2, clot solubility normalized as measured by clot lysis in urea. Clot strength and resistance to fibrinolysis, as assessed by thromboelastography, also improved. Safety reviews were conducted before each dose escalation; no serious adverse events, including bleeding or thrombosis, were noted during the study. In addition, there was no evidence of the generation of specific antibodies to rFXIII or yeast proteins. Recombinant FXIII appears to be a safe and potentially effective alternative for FXIII replacement in patients with FXIII deficiency.