Exposure–response for biomarkers of anticoagulant effects by the oral direct thrombin inhibitor AZD0837 in patients with atrial fibrillation

AIMS: AZD0837 is a novel oral anticoagulant investigated in clinical studies for stroke prevention in patients with atrial fibrillation (AF). It is bioconverted to its active form, AR-H067637, a potent, specific and reversible thrombin inhibitor. The effects on coagulation biomarkers were correlated with the pharmacokinetic (PK) exposure of AR-H067637 to guide selection of the effective dose regimen for a confirmatory efficacy study in AF patients. METHODS: Blood samples were obtained from 601 AF patients randomized to one of four doses of AZD0837 (blinded treatment) or dose-adjusted vitamin K antagonists (VKA, open treatment) for 3-9 months. A pharmacodynamic model was developed to describe the time course of the AR-H067637 exposure dependent effects and the effect of VKA on fibrin D-dimer. The thrombin generation measured ex vivo in venous plasma was also investigated. RESULTS: The PK exposure of AR-H067637 was stable with an interindividual variability of 33% and no or minor influence of patient demographics or comedications. For AZD0837, D-dimer levels decreased with more rapid onset than for VKA. The decrease in D-dimer levels correlated with steady-state plasma concentrations (C(ss)) of AR-H067637, with a maximum decrease of baseline D-dimer levels estimated to approximately 60% for both AZD0837 and VKA therapy. The effect on thrombin generation correlated closely with the plasma concentration of AR-H067637. CONCLUSIONS: The effects on thrombin generation and fibrin D-dimer levels correlated with the plasma concentration of its active form and provided comparable effects to well-controlled VKA therapy at an exposure at least corresponding to the 300 mg once daily dose of AZD0837.