Monitoring direct FXa-inhibitors and fondaparinux by Prothrombinase-induced Clotting Time (PiCT): relation to FXa-activity and influence of assay modifications.
ABSTRACT FXa-activity can be measured by the Prothrombinase induced Clotting time (PiCT). The manufactured assay uses bovine FXa as component and employs a incubation period before re-calcification. Its use with new direct FXa-inhibitors is challenged by reports on decreased sensitivity.
Blood was incubated with 3 investigational, structurally related (oxazolidinones) direct FXa-inhibitors including the recently approved agent rivaroxaban (0 - 2.0 microM), with the structurally distinct direct FXa-inhibitor DX 9065a (0 - 18 microM) and with the indirect inhibitor fondaparinux (0 - 0.6 microM). We tested modifications of PiCT regarding the source of FXa (bovine or human) and the incubation step (incubation before re-calcification=2-step, no incubation =1-step), and compared results with inhibition of human or bovine FXa-activity.
The bovine 2-step PiCT showed a paradoxical decrease with all direct FXa-inhibitors, this effect is surmounted only at high concentrations and is not seen with the bovine 1-step PiCT. The decrease in PiCT is not observed in antithrombin-depleted plasma. The humanized PiCT (1 or 2 step) showed a consistent prolongation under all direct inhibitors. Fondaparinux prolonged PiCT with either assay. The correlation between PiCT and corresponding FXa-activity was significant both for humanized 2-step PiCT or bovine 1 step PiCT (r2=0.80), but the 95% prediction interval was large and covered a span of 40% FXa-activity between one agent and another.
The customary bovine PiCT should only be used to monitor direct FXa-inhibitors when modified as 1-step procedure. PiCT is not suitable to assess similarity of FXa-inhibition when different agents are interchanged.
- Thrombosis Research 06/2002; 106(3):V267-73. · 3.13 Impact Factor
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ABSTRACT: Rivaroxaban (BAY 59-7939) is an oral, direct factor Xa inhibitor in advanced development. This study was undertaken to investigate its effects on thrombin generation. In this placebo-controlled, randomized, crossover study, 12 healthy subjects received rivaroxaban (single 5- or 30-mg dose) or placebo. Thrombin generation was investigated by measuring the endogenous thrombin potential and prothrombinase-induced clotting time. Maximal effect of rivaroxaban was observed 2 hours after drug administration: prothrombinase-induced clotting time was prolonged 1.8 and 2.3 times baseline after rivaroxaban 5 and 30 mg, respectively. Collagen-induced endogenous thrombin potential was reduced by approximately 80% and approximately 90% compared with baseline after rivaroxaban 5 and 30 mg, respectively, and tissue factor-induced endogenous thrombin potential was reduced by approximately 40% (5 mg) and approximately 65% (30 mg), respectively. Thrombin generation remained inhibited for 24 hours. There was a close correlation between plasma concentration of rivaroxaban and prolongation of prothrombinase-induced clotting time and reduction in endogenous thrombin potential. Rivaroxaban strongly inhibits platelet-induced thrombin generation, after activation of either platelets or the coagulation pathway, even in the presence of minimal factor Xa inhibition in plasma.The Journal of Clinical Pharmacology 12/2007; 47(11):1398-407. · 2.84 Impact Factor
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ABSTRACT: Despite recent progress in antithrombotic therapy, there is still an unmet medical need for safe and orally available anticoagulants. The coagulation enzyme Factor Xa (FXa) is a particularly promising target, and recent efforts in this field have focused on the identification of small-molecule inhibitors with good oral bioavailability. We identified oxazolidinone derivatives as a new class of potent FXa inhibitors. Lead optimization led to the discovery of BAY 59-7939 (5), a highly potent and selective, direct FXa inhibitor with excellent in vivo antithrombotic activity. The X-ray crystal structure of 5 in complex with human FXa clarified the binding mode and the stringent requirements for high affinity. The interaction of the neutral ligand chlorothiophene in the S1 subsite allows for the combination of good oral bioavailability and high potency for nonbasic 5. Compound 5 is currently under clinical development for the prevention and treatment of thromboembolic diseases.Journal of Medicinal Chemistry 10/2005; 48(19):5900-8. · 5.61 Impact Factor