Assay Dependent Reversal of the Oral and Parenteral Anti-Xa Agents By Andexanet Alfa

Introduction: Andexanet alfa (AA, Portola Pharmaceuticals, San Francisco, USA) is an approved reversal agent for the control of potential bleeding associated with apixaban and rivaroxaban. Beside the oral anti-Xa agents, parenteral forms of the inhibitors of factor Xa such as otamixaban (Sanofi Aventis, Paris, France) and DX9065a (Mitsubishi Pharmaceuticals, Tokyo, Japan) have also been developed. These agents represent synthetic organo-mimerics with comparable selectivity and inhibitory profile to the currently available oral anti-Xa agents. Parenteral anti-Xa agents are considered for clinical development. Andexanet alfa is a broad-spectrum neutralizing agent for anti-Xa drugs including heparin and heparino-mimerics. We hypothesized that andexanet alfa may also reverse the effects of such parenteral anti-Xa agents as otamixaban and DX9065a. This study is designed to compare the neutralization profile of andexanet alfa for apixaban and rivaroxaban with otamixaban and DX9065a in various laboratory assays.

Materials and Method: Apixaban, rivaroxaban, otamixaban and DX9065a were commercially obtained in powdered form and diluted in 0.9 % sodium chloride to make stock solution of 1.0 mg/ml. Andexanet alfa was obtained from the hospital pharmacy. Drugs were supplemented in plasma in the concentration range of 0.0 – 1.0 ug/ml. Individual aliquots of samples were supplemented with either saline or andexanet alfa at a final concentration of 100 ug/ml. Factor Xa activity was measured by using an amidolytic method. For clotting profile, prothrombin time (PT) and activated partial thromboplastin time were measured. Thrombin generation studies were carried out using a calibrated automated thrombogram (CAT, Diagnostica Stago, Paris, France). Such parameters as peak thrombin (PT), area under the curve (AUC) and lag time (LT) were measured. The inhibitory effects of each of these agents towards factor Xa were calculated and their reversal by andexanet alfa was determined. Results were compiled as mean SD of 3 individual determination.

Result: Both the oral and parenteral anti-Xa agents produced a concentration dependent inhibition of factor-Xa with the IC50 values ranging from 0.17 - 1.1 ug/ml in control group. Supplementation of andexanet alfa at 100 ug/ml resulted in the neutralization of the anti-Xa activities of these agents with the IC50 values ranging from 0.22 - 1.1 ug/ml. Andexanet alfa did not produce any reversal of the anti-Xa activities of DX9065a. In the thrombin generation studies, Apixaban, rivaroxaban and otamixaban produced strong concentration dependent inhibition of thrombin formation. However, DX9065a produced relatively weaker anti-Xa effects. The IC50 values varied with apixaban (0.08 ug/ml), rivaroxaban (0.22 ug/ml), otamixaban (0.6 ug/ml) and DX9065a (>2.5 ug/ml). In the clot-based prothrombin time assay all agents produced a concentration dependent prolongation of PT in the range of 0 - 1 ug/ml. Andexanet alfa at 100 ug/ml produced a complete neutralization of apixaban, rivaroxaban and otamixaban, whereas it partially neutralized the anticoagulant effects of DX9065a in this assay. The parenteral anticoagulants otamixaban and DX9065a produced a much stronger anticoagulant effects in the aPTT assay in comparison to both apixaban and rivaroxaban. Andexanet alfa at 100 ug/ml effectively neutralized the anticoagulant effects of otamixaban in comparison to Apixaban and rivaroxaban. Whereas DX9065a were not neutralized. Table 1 shows the composite results for the neutralization of oral and parenteral anti-Xa agents at 0.5 ug/ml by andexanet alfa at 100 ug/ml.

Conclusion: Our results suggest that andexanet alfa is capable of neutralizing the effects of potent parenteral anti-Xa agents such as otamixaban in an assay dependent fashion. The data also points to the varying inhibitory effects of anti-Xa agents which are differentially neutralized by andexanet alfa. These results also underscore that the in-vitro anti-Xa potency of both the oral and parenteral anti-Xa agents does not fully reflect their inhibitory effects on the overall coagulation process. Nevertheless, andexanet alfa may be a useful agent in the neutralization of parenteral anti-Xa agents.