Effects of the oral, direct factor Xa inhibitor apixaban on routine coagulation assays and anti-FXa assays

IntroductionApixaban is an oral direct factorXa inhibitor developed for the prophylaxis and treatment of thromboembolic disorders. Laboratory monitoring is not necessary, but the effects on common coagulation reagents and assays constitute clinically valuable information. ObjectivesTo investigate the effects of apixaban on commonly used coagulation methods, and to evaluate anti-FXa assays for specific determination of the drug concentration. Materials and MethodsApixaban was added to plasma from healthy subjects in the concentration range 0-1000gL(-1), and analyses were performed with different reagents for activated partial thromboplastin time (APTT), prothrombin time (PT), antithrombin, proteinC, and proteinS. A lupus anticoagulant assay and an APTT assay with varying phospholipid concentrations were used to study the phospholipid dependence. ResultsIn general, apixaban showed fewer effects invitro than have been shown for rivaroxaban, another direct FXa inhibitor. The concentration needed to double the APTT varied between 2200 and 4700gL(-1), and the concentration needed to double the PT varied between 700 and 3900gL(-1). The effects on antithrombin, proteinC and proteinS assays were dependent on the type of reagent. Apixaban did not cause false-positive lupus anticoagulant results. Chromogenic anti-FXa assays showed linear dose-response curves with apixaban. ConclusionsTherapeutic concentrations of apixaban variably affect different assay groups, and even different reagents within an assay group. The effects were much smaller than with rivaroxaban. The use of APTT and/or PT assays to screen the anticoagulant activity of apixaban cannot be recommended. A chromogenic anti-FXa assay can be used for reliable measurements of apixaban concentration.