Monitoring plasma levels of factor Xa inhibitors: how, why and when?

Abstract

New oral anticoagulants are directed towards a single target, essentially factor Xa (FXa) or factor IIa. They do not require routine coagulation monitoring. However, in special clinical settings (emergency surgery, bleeding, thrombosis, control of the patient’s compliance, suspected overdose, potential drug interference, and so on), measurement of plasma levels is needed. Several available anti-FXa assays are used for monitoring anticoagulant activity of heparins and fondaparinux. They must be modified and standardized for the measurement of direct FXa inhibitors (rivaroxaban, apixaban, edoxaban, betrixaban and others). The use of calibrators (lyophilized plasma with a known concentration of drug) allows an expression of the results in ng per ml of plasma. Two categories of assays – endogenous and exogenous assays are available. Endogenous assays are useful in pharmaceutical research, while exogenous assays are used in clinical laboratories. The preferred anti-FXa assay is a specific method in contrast to prothrombin time and activated partial thromboplastin time, but it is not available everywhere at any time. A specific measurement of direct FXa inhibitors is feasible with the use of a new test developed by the authors’ group. The physicians must be aware of the possibility to measure the plasma concentration of FXa inhibitors in patients at high risk of bleeding and in several other special clinical situations.

Keywords::

• antifactor Xa
• apixaban
• calibrators
• fondaparinux
• heparins
• rivaroxaban

Financial & competing interests disclosure

MM Samama, C Guinet and L Le Flem are employees of Biomnis Laboratories. MM Samama serves as a consultant for Bayer Schering Pharma AG, Sanofi-Aventis, Eli Lilly and Daiichi Sankyo, is, a member of advisory board/steering committee for Bristol–Myers Squibb, Pfizer Laboratory and Johnson & Johnson, and an invited speaker/chairperson for Sanofi-Aventis, GlaxoSmithKline, Bayer Schering Pharma AG, Boehringer Ingelheim, Rovi Laboratory and TEM. J Amiral is employee at Hyphen Biomed Company. J Seghatchian is a freelance consultant advisor in blood component technology and thrombosis/hemostasis. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.