[Assessment of anti-factor Xa activity for heparin and related products by chromogenic assays and thrombin generation...

Anticoagulant therapy is widely used for the prevention and treatment of thromboembolism. In addition to established agents such as warfarin, unfractionated heparin and low-molecular-weight heparins, a variety of new anticoagulant drugs has been introduced for clinical use, including direct thrombin inhibitors and factor Xa inhibitors. These new drugs can be given at fixed doses without the need for routine monitoring of the coagulation profile. However, an assays to evaluate anticoagulant strength would be valuable to prevent undesired hemorrhagic or thromboembolic events during treatment. In the present study, we examined the feasibility of several laboratory monitoring tests, including chromogenic-based anti-factor Xa assay and the thrombin generation test to determine the anticoagulant effect of low-molecular-weight heparins and fonda-parinux. Dose-dependent relationship between anti-factor Xa activity and the concentration of fondaparinux was observed by the chromogenic assays. In the thrombin generation test, the peak parameter seemed to be more informative than the endogenous thrombin potential, which corresponds to the total amount of thrombin activity, to assess the pharmacodynamic effects. In summary, our study suggested that both assays may be useful for quantitative determination of factor Xa activity. Further studies are necessary to develop and establish simpler methods that can be used in routine laboratory testing to monitor treatment with the newer anticoagulant drugs.