Effects of ximelagatran,an oral direct thrombin inhibitor,r-hirudin and enoxaparin on thrombin generation and platelet activation in healthy male subjects

OBJECTIVES: The effects of ximelagatran, an oral direct thrombin inhibitor (DTI), recombinant hirudin (r-hirudin) and enoxaparin on thrombin generation and platelet activation were studied in humans. BACKGROUND: Recombinant hirudin (parenteral DTI) and enoxaparin (low molecular weight heparin) have been demonstrated to be clinically effective in acute coronary syndromes. Ximelagatran is currently under investigation for the prevention and treatment of thromboembolism. The shed blood model allows for the study of thrombin generation and platelet activation in humans in vivo. METHODS: This was an open-label, parallel-group study involving 120 healthy male volunteers randomized to receive one of three oral doses of ximelagatran (15, 30 or 60 mg), r-hirudin (intravenous) or enoxaparin (subcutaneous) at doses demonstrated to be clinically effective in acute coronary syndromes, or to serve as a control. Thrombin generation (prothrombin fragment 1+2 [F1+2] and thrombin-antithrombin complex [TAT]) and platelet activation (beta-thromboglobulin [beta-TG]) biomarkers were studied using a shed blood model involving blood collection from skin incisions made using standardized bleeding time devices. RESULTS: Oral ximelagatran, intravenous r-hirudin and subcutaneous enoxaparin rapidly and significantly (p < 0.05) decreased F1+2, TAT and beta-TG levels in shed blood, indicating inhibition of thrombin generation and platelet activation. Statistically significant concentration (melagatran, the active form of ximelagatran)-response relationships for F1+2 (p = 0.005), TAT (p = 0.005) and beta-TG (p < 0.001) levels, with IC(50)s of 0.376 (F1+2), 0.163 (TAT) and 0.115 (beta-TG) micromol/l, were detected. Melagatran showed dose-proportional pharmacokinetics with low variability. All drugs were well tolerated. CONCLUSIONS: Oral administration of the DTI ximelagatran resulted in a rapid inhibition of both thrombin generation and platelet activation in a concentration-dependent manner using a human shed blood model. The inhibition of thrombin generation by 60 mg ximelagatran was comparable to that observed with doses of r-hirudin and enoxaparin demonstrated to be effective for the treatment of acute coronary syndromes.     

Transition from argatroban to oral anticoagulation with phenprocoumon or acenocoumarol: effect on coagulation factor testing

Treatment with the thrombin inhibitor argatroban is often followed by vitamin K-antagonist treatment. In this study, the behavior of coagulation factors measured under these treatment regimens is shown. Healthy subjects received infusions of 1.0, 2.0, or 3.0 microg/kg/hr argatroban before and during phenprocoumon or acenocoumarol dosing. Quantitation of factors II, VII, IX, and X by clot-based assays resulted in dose dependent, approximately 20%, lower than expected values in the presence of argatroban. On the contrary, values for the inhibitors, protein C and protein S, were higher. Cotherapy exaggerated the effect by vitamin K-antagonist alone. However, testing by immunologic and chromogenic assays did not show any effect by argatroban. Coupled with a lack of bleeding in the subjects, these data suggests that argatroban does not affect coagulation proteins and that the observations are only an assay artifact. Assay interferences must be considered when measuring coagulation proteins in patients receiving thrombin inhibitors.     

Effects of melagatran, the active form of the oral direct thrombin inhibitor ximelagatran, and dalteparin on the endogenous thrombin potential in venous blood from healthy male subjects.

The effect of the oral direct thrombin inhibitor ximelagatran and its active form, melagatran, on thrombin generation was investigated in vitro and ex vivo using a thrombin generation assay. In-vitro thrombin generation was triggered in human platelet-poor plasma by the addition of tissue factor, and the endogenous thrombin potential (ETP) was measured. The ETP IC(50) values for melagatran and the low-molecular-weight heparin dalteparin were 0.44 micromol/l and 0.06 IU/ml, respectively. In contrast to dalteparin, melagatran increased the time-to-thrombin peak in a concentration-dependent manner. ETP was also studied ex vivo in platelet-poor plasma collected from healthy male subjects (n = 54) at pre-dose and 2 h post-dose, with ximelagatran (60 mg) orally, dalteparin (120 IU/kg) subcutaneously, or control (water) orally. After ximelagatran or dalteparin administration, the time-to-thrombin peak was prolonged by 41 and 95%, and the ETP was decreased by 61 and 77%, respectively. Thus, melagatran, the active form of the oral direct thrombin inhibitor ximelagatran, efficiently delays and inhibits the generation of thrombin in plasma both in vitro and ex vivo.     

肝功能障碍营养治疗

各种原因引起的肝功能障碍会引起不同程度的机体能量及多种营养素代谢障碍,在肝病早期就会出现营养不良。肝病患者营养不良的早期诊断、早期治疗很重要,为此需对肝病患者的营养状态进行全面客观的评估,做出营养诊断,旨在指导营养治疗。适宜的营养治疗可以提供肝功能障碍患者代谢需要的能量和营养素,维持或改善肝脏功能,加快肝细胞自身修复,促进细胞新生,改善机体代谢状态。文章将就肝功能障碍患者的营养代谢特点、营养状态评估及营养治疗进行综述。     

Compliance and adherence to oral anticoagulation therapy in elderly patients with atrial fibrillation in the era of direct oral anticoagulants

Elderly patients with atrial fibrillation usually have more concomitant conditions that affect compliance and adherence to anticoagulant therapy. Direct oral anticoagulants seem to be associated with better adherence; however, there is still room to improve continuous coagulation control and adherence among elderly patients receiving anticoagulants in everyday practice.     

Effect of emicizumab on global coagulation assays for plasma supplemented with apixaban or argatroban

Journal of Thrombosis and Thrombolysis - Emicizumab is a bi-specific humanized monoclonal antibody mimicking the factor (F) VIII cofactor activity in mediating the activation of FX by FIXa. Recent...     

Level of protein C determined by combined assays during disseminated intravascular coagulation and oral anticoagulation

We have developed a variation of the solid-phase enzyme-linked immunosorbent assay (ELISA) to enable measurement of the activity and antigen levels of protein C (PC) in human plasma. With this assay it is possible to do both tests with the same sample and same microtiter plate coated with anti-PC monoclonal antibody (MCA)JTC-4, which inhibited neither activation of PC nor activity of activated PC (APC). Even in patients undergoing heparin treatment for severe disseminated intravascular coagulation, there were no detectable differences between amidolytic activity and antigen levels of PC in patients' plasma. In addition, there was a strong correlation between the immunologic levels of PC in patients' plasma determined both by polyclonal ELISA using peroxidase-labeled immunopurified antiprotein C-IgG and those found with MCA ELISA using peroxidase-labeled MCAJTC-5, which does not bind to APC. In contrast, when oral anticoagulation therapy was started, immunologic levels of plasma PC estimated by peroxidase-labeled MCAJTC- 1, a MCA that recognizes a gamma-carboxyglutamic acid domain-related conformational change of PC induced by metal ions, decreased more rapidly than did either the PC level determined by polyclonal ELISA or the percent prothrombin time. This suggested that comparison of MCAJTC- 1-recognized PC levels and prothrombin time may be necessary at the beginning of oral anticoagulation therapy to treat patients safely.     

Influence of coagulation factors on extrinsic thrombin generation.

The extrinsic coagulation activity assay (EXCA) is a new thrombin generation test for the tissue factor pathway of coagulation. The EXCA was performed with 10 parts citrated plasma of different contents of fibrinogen. One part tissue factor, 250 mmol/l CaCl(2), generating about 1 IU/ml thrombin within 1 min (37 degrees C). After 0-30 min 2.5 mol/l arginine (pH 8.6) Generated thrombin was detected by addition of CHG-Ala-Arg-pNA and measurement of triangle upA/t. The EXCA is dependent on factors 10% of the factor VII norm in the sample achieves 70-80% of the thrombin generation norm. The EXCA is not dependent on factors VIII, IX, XI and XII. Even in antithrombin III-deficient plasma, a phase of thrombin inhibition appears after the thrombin peak. Supplemented purified fibrinogen resulted in decreased thrombin generation in the important. Fibrinogen seems to act as antithrombin I; thrombin might be entrapped in the nascent fibrin. The EXCA is suitable to diagnose the level of extrinsic factors in patient plasma.     

Influence of coagulation factors on intrinsic thrombin generation.

The intrinsic coagulation activity assay (INCA) is a new thrombin-generation test that imitates the intrinsic pathway of blood coagulation. The aim of the present study was to investigate the influence of the main coagulation factors on the INCA. The INCA was performed with citrated plasma samples supplemented with different amounts of fibrinogen. The INCA and activated partial thromboplastin time determination were performed with factor-depleted plasmas and with mixtures of depleted plasmas with normal plasma. Supplemented purified fibrinogen resulted in a decrease of intrinsic thrombin generation (50% inhibitory concentration = 0.8 g/l). The INCA depends on the intrinsic factors (factors VIII, IX, XI and XII) and on the factors of the common pathway (factors II, V and X): for normal thrombin generation, at least about 50% of normal factor II is necessary. For the majority of factors, the sensitivity of the INCA appears to be approximately one order of magnitude better than that of the activated partial thromboplastin time. The INCA allows one to diagnose defects in the intrinsic coagulation system and might be a useful test to support development and characterization of new drugs targeted at the intrinsic generation of thrombin.     

Treatment with an oral direct thrombin inhibitor decreases platelet activity but increases markers of inflammation in patients with myocardial infarction

Abstract. Christersson C, Oldgren J, Wallentin L, Siegbahn A (Uppsala University, Uppsala, Sweden). Treatment with an oral direct thrombin inhibitor decreases platelet activity but increases markers of inflammation in patients with myocardial infarction. J Intern Med 2011; 270 : 215–223. Background. Thrombin has a role not only in the coagulation process but also in inflammatory responses. Oral direct thrombin inhibitors (DTIs) are currently being evaluated in patients with thromboembolic diseases. Objective. To investigate whether an oral DTI affects markers for platelet and inflammatory activity after myocardial infarction (MI). Methods. A total of 518 patients with MI were randomly assigned to ximelagatran treatment (four different dose groups) in combination with aspirin, or aspirin alone for 6 months. The levels of soluble (s) P‐selectin, soluble tissue factor, C‐reactive protein (CRP), interleukin (IL)‐10 and IL‐18 were analysed in serial blood samples. Results. sP‐selectin concentration increased after 1 week and persisted at an elevated level for 6 months in all study groups (P < 0.001). In the two highest ximelagatran dose groups, there was a reduced increase in sP‐selectin compared to treatment with lower doses of ximelagatran and aspirin alone (P = 0.01 and P = 0.002, respectively). IL‐18 levels did not change in the aspirin alone treatment group. By contrast, there was an elevation in IL‐18 level in the lower and higher ximelagatran dose groups after 6 months (P = 0.006 and P < 0.001, respectively). Ximelagatran increased IL‐10 levels (P = 0.002) and reduced the decrease in CRP levels after 6 months compared to treatment with aspirin alone (P = 0.002). Conclusion. A persistent elevation of platelet activity is found in patients with a recent MI after the cessation of acute antithrombotic treatment, and the addition of an oral DTI at higher doses decreases the activity. By contrast, long‐term treatment with a DTI increases the levels of several markers of inflammation. Further studies with prolonged exposure of oral DTIs are needed for evaluation of the effect on inflammatory processes and to determine whether these agents influence clinical outcomes.     

Anticoagulant properties, clinical efficacy and safety of efegatran, a direct thrombin inhibitor, in patients with unstable angina.

AIMS: Thrombin plays a key role in the clinical syndrome of unstable angina. We investigated the safety and efficacy of five dose levels of efegatran sulphate, a direct thrombin inhibitor, compared to heparin in patients with unstable angina. METHODS: Four hundred and thirty-two patients with unstable angina were enrolled. Five dose levels of efegatran were studied sequentially, ranging from 0.105 mg. kg(-1). h(-1)to 1.2 mg. kg(-1). h(-1)over 48 h. Safety was assessed clinically, with reference to bleeding and by measuring clinical laboratory parameters. Efficacy was assessed by the number of patients experiencing any episode of recurrent ischaemia as measured by computer-assisted continuous ECG ischaemia monitoring. Clinical end-points were: episodes of recurrent angina, myocardial infarction, coronary intervention (PTCA or CABG), and death. RESULTS: Efegatran demonstrated dose dependent ex-vivo anticoagulant activity with the highest dose level of 1.2 mg. kg(-1). h(-1)resulting in steady state mean activated partial thromboplastin time values of approximately three times baseline. Thrombin time was also increased. Neither of the efegatran doses studied were able to suppress myocardial ischaemia during continuous ECG ischaemia monitoring to a greater extent than that seen with heparin. There were no statistically significant differences in clinical outcome or major bleeding between the efegatran and heparin groups. Minor bleeding and thrombophlebitis occurred more frequently in the efegatran treated patients. CONCLUSION: Administration of efegatran sulphate at levels of at least 0.63 mg. kg(-1). h(-1)provided an anti-thrombotic effect which is at least comparable to an activated partial thromboplastin time adjusted heparin infusion. There was no excess of major bleeding. The level of thrombin inhibition by efegatran, as measured by activated partial thromboplastin time, appeared to be more stable than with heparin. Thus, like other thrombin inhibitors, efegatran sulphate is easier to administer than heparin. However, no clinical benefits of efegatran over heparin were apparent.     

Risk of falls and major bleeds in patients on oral anticoagulation therapy

BackgroundThe risk of falls is the most commonly cited reason for not providing oral anticoagulation, although the risk of bleeding associated with falls on oral anticoagulants is still debated. We aimed to evaluate whether patients on oral anticoagulation with high falls risk have an increased risk of major bleeding.MethodsWe prospectively studied consecutive adult medical patients who were discharged on oral anticoagulants. The outcome was the time to a first major bleed within a 12-month follow-up period adjusted for age, sex, alcohol abuse, number of drugs, concomitant treatment with antiplatelet agents, and history of stroke or transient ischemic attack.ResultsAmong the 515 enrolled patients, 35 patients had a first major bleed during follow-up (incidence rate: 7.5 per 100 patient-years). Overall, 308 patients (59.8%) were at high risk of falls, and these patients had a nonsignificantly higher crude incidence rate of major bleeding than patients at low risk of falls (8.0 vs 6.8 per 100 patient-years, P = .64). In multivariate analysis, a high falls risk was not statistically significantly associated with the risk of a major bleed (hazard ratio 1.09; 95% confidence interval, 0.54-2.21). Overall, only 3 major bleeds occurred directly after a fall (incidence rate: 0.6 per 100 patient-years).ConclusionsIn this prospective cohort, patients on oral anticoagulants at high risk of falls did not have a significantly increased risk of major bleeds. These findings suggest that being at risk of falls is not a valid reason to avoid oral anticoagulants in medical patients.     

Pharmacokinetics and anticoagulant effect of the direct thrombin inhibitor melagatran following subcutaneous administration to healthy young men.

The pharmacokinetic dose linearity and reproducibility, the effects on ex-vivo coagulation time assays and bleeding time, and tolerability of the direct thrombin inhibitor melagatran following subcutaneous (s.c.) dosing were investigated in two open-label studies in healthy males: (i). a dose-escalation study in which subjects received single s.c. doses of melagatran (0.1-5 mg); and (ii). a repeated-dosing study in which 3 mg s.c. melagatran was administered at 12-h intervals for 4 days. In both studies, melagatran was rapidly absorbed with maximum plasma concentrations (C(max)) observed about 0.5 h post dosing. The half-life of melagatran was about 2 h. The area under the melagatran plasma concentration versus time curve increased linearly with dose. No time dependency in the area under the curve or Cmax was observed over 4 days of twice-daily dosing. The variability in pharmacokinetic parameters was low and the bioavailability of melagatran appeared to be complete. There was a steep and linear prolongation of thrombin time, a non-linear prolongation of both activated partial thromboplastin time and activated coagulation time, and a decrease in prothrombin complex activity with increasing melagatran plasma concentration. Only moderate increases in capillary bleeding time were observed with s.c. doses up to 5 mg melagatran. Melagatran was well tolerated after s.c. injection, with good local tolerability at the injection site.     

In vitro studies using a global hemostasis assay to examine the anticoagulation effects in plasma by the direct thrombin inhibitors: dabigatran and argatroban

This study aimed to assess whether a global hemostatic assay we developed can measure the anticoagulant effects of the direct thrombin inhibitors (DTIs)—dabigatran and argatroban. A normal plasma pool (NPP) spiked with one of the DTIs and five plasma samples from patients with coronary heart disease spiked with dabigatran were examined. Fibrin formation and fibrin degradation were initiated by adding recombinant tissue factor (together with washed-frozen-thawed platelets and CaCl₂) and recombinant tissue plasminogen activator. Fibrin optical density (OD) was recorded, based on which coagulation activation profile (Cp) and fibrinolysis activation profile (Fp) were determined. Moreover, the sum of OD values registered over time (fibrin OD-sum) was calculated to reflect the capacity of fibrin formation under the general effect by Cp and Fp. The endogenous thrombin potential (ETP) and the standard clotting markers i.e., activated partial thromboplastin time (APTT) and prothrombin time expressed as International Normalized Ratio (INR) were also analyzed. Results demonstrated that APTT, INR and ETP could detect the effects of the DTIs except for INR in NPP containing dabigatran. In our global assay, the DTIs depressed the fibrin formation (shown as decreased fibrin OD-sum value) by leading to decrease of Cp and increase of Fp. Thus, our global assay which examines both fibrin formation and degradation seems more advantageous than the other methods mentioned above, as regards the possibility of being a laboratory tool to monitor the antithrombotic therapy with DTIs.     

Bleeding risk and major adverse events in patients with previous ulcer on oral anticoagulation therapy

Bleeding is the major concern for patients receiving oral anticoagulation therapy (OAT), especially those with histories of gastrointestinal ulcer. The aim of this study was to evaluate the efficacy and safety of OAT in patients with nonvalvular atrial fibrillation with histories of ulcer. A composite end point, including major adverse cardiac events or major bleeding, was compared between patients with AF with previous ulcers who were (OAT+; n = 200) and were not (OAT- n = 230) receiving OAT. During the follow-up period of 3.3 ± 2.7 years, 28 (14%) and 66 (29%) OAT+ and OAT- patients, respectively, had major adverse cardiac events (p = 0.001). Major bleeding occurred in 46 OAT+ patients (23%) and 25 OAT- patients (11%) (p = 0.001). There was no significant difference in the composite end point between OAT+ and OAT- patients (29% vs 36%, p = 0.08). The incidence of major bleeding was significantly lower, decreasing from 30% to 14%, when OAT began after endoscopic confirmation of ulcer healing (p = 0.02). OAT+ patients who achieved time in the therapeutic range ≥60% for international normalized ratio (2.0 to 3.0) demonstrated better cumulative survival free from the composite end point than OAT- patients (p = 0.01). In conclusion, OAT in patients with nonvalvular AF with histories of gastrointestinal ulcer made no difference in the composite end point compared to absence of OAT. In OAT+ patients, maintaining an optimal international normalized ratio reduced the composite end point, and the confirmation of ulcer healing reduced the incidence of bleeding.     

Bleeding profiles of anticoagulants, including the novel oral direct thrombin inhibitor ximelagatran: definitions, incidence and management

Ximelagatran is a novel oral direct thrombin inhibitor (oral DTI) that is currently in advanced clinical development for the prevention and treatment of thromboembolic events in a wide range of patient populations and indications. The clinical development of novel anticoagulant therapies requires that treatments be assessed according to both their clinical benefit (reduction of risk of thromboembolic events) and safety profile (primarily bleeding). Definition and assessment of bleeding severity is thus an important factor in clinical trial design. Lack of consistency in bleeding definitions used in different clinical trial programmes makes comparison of bleeding event data difficult. Standard bleeding definitions would be required to make fair comparisons between clinical trials possible. The definitions of bleeding events used in clinical trials of ximelagatran are broadly consistent with those used in many other major trials. Results of phase II and III trials comparing ximelagatran with currently available anticoagulant therapies demonstrate that ximelagatran can be used with fixed dosing with no coagulation monitoring, dose titration, or dose adjustment, without compromising efficacy or safety. The incidences of major bleeding events in clinical trials of ximelagatran have been low and similar to those with other anticoagulant drugs. Adequate treatment in case of emergency situations such as serious bleeding should include cessation of treatment and maintenance of adequate diuresis.