Abstract
Research into new anticoagulants for preventing and treating thromboembolic disorders has focused on targeting single enzymes in the coagulation cascade, particularly Factor Xa and thrombin, inhibition of which greatly decreases thrombin generation. Based on the results of phase III clinical trials, rivaroxaban, a direct Factor Xa inhibitor, has been approved in many countries for the management of several thromboembolic disorders. Owing to its predictable pharmacokinetic and pharmacodynamic characteristics, fixed-dose regimens are used without the need for routine coagulation monitoring. In situations where assessment of rivaroxaban exposure may be helpful, anti-Factor Xa chromogenic assays (in tandem with standard calibration curves generated with the use of rivaroxaban calibrators and controls) could be used. It is important to note that test results will be affected by the timing of blood sampling after rivaroxaban intake. In addition, the anti-Factor Xa method measures the drug concentration and not the intensity of the drug’s anticoagulant activity, and a higher than expected rivaroxaban plasma level does not necessarily indicate an increased risk of bleeding complications. Therefore, clinicians need to consider test results in relation to the pharmacokinetics of rivaroxaban and other patient risk factors associated with bleeding.
Highlights
Traditional anticoagulant agents such as vitamin K antagonists (VKAs), unfractionated heparin (UFH), low molecular weight heparins and fondaparinux have been widely used in the prevention and treatment of thromboembolic diseases
Rivaroxaban is approved in the European Union (EU) and North America for the treatment of deep vein thrombosis (DVT) and pulmonary embolism, and prevention of recurrent DVT and pulmonary embolism in adults, and is approved in the EU, in combination with antiplatelet agents, for the prevention of atherothrombotic events in adults who have acute coronary syndromes and elevated cardiac biomarkers [3,4,9]
Results were reported in a field trial of 18 centres that compared prothrombin time (PT) results from different laboratories using different local reagents versus one central reagent and local instruments. This trial reported inter-laboratory variation in mean PT values that was significantly reduced by use of a centrally provided PT reagent (STA® Néoplastine CI Plus [Diagnostica Stago]) and when results were expressed as rivaroxaban concentrations [40]
Summary
Traditional anticoagulant agents such as vitamin K antagonists (VKAs), unfractionated heparin (UFH), low molecular weight heparins and fondaparinux have been widely used in the prevention and treatment of thromboembolic diseases. This trial reported inter-laboratory variation in mean PT values that was significantly reduced by use of a centrally provided PT reagent (STA® Néoplastine CI Plus [Diagnostica Stago]) and when results were expressed as rivaroxaban concentrations (μg/l) [40] This method may be sensitive enough to measure peak rivaroxaban plasma concentrations that would occur after currently approved therapeutic doses, i.e. provide a qualitative confirmation of the presence of rivaroxaban [37]. Accumulating data indicate that anti-Factor Xa chromogenic assays (with use of rivaroxaban calibrators and controls) are able to measure a wide range of rivaroxaban concentrations encompassing the entire range after therapeutic dosing [1,2,24]. The timing of blood sampling after tablet intake is important because levels of rivaroxaban change markedly over time owing to the pharmacokinetics of the drug (e.g. levels of rivaroxaban will differ greatly 2–4 hours versus 24 hours after dosing)
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