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Clinical Development Phases I-III Regulatory, Quality, Manufacturing Treatment with new oral anticoagulant drugs does not require laboratory monitoring. However, there are some clinical settings where the measurement of the anticoagulant activity can be useful, especially in urgent surgery or invasive procedure. Prothrombin time (PT) and activated partial thromboplastin time (aPTT) are prolonged with good correlation with plasma drug concentration. The influence of rivaroxaban on PT is greater than that on aPTT, in contrast to dabigatran. Apixaban responses to PT and aPTT are weak. These tests are not specific and cannot detect low plasma concentrations. For direct Factor-Xa inhibitors, the most appropriate test is a modified anti-Xa chromogenic assay. A specific test unresponsive to heparins and fondaparinux has been developed. For dabigatran measurement, a modified thrombin clotting time, “Hemoclot,” has been well documented. The use of plasma calibrators allows an expression of the results in ng/ml of plasma. Expected peak concentration (2 to 4 h after drug intake) and trough concentration or Cmin—before a repeated administration—have been determined. More clinical work is warranted to determine possible adjustments of the drug according to its plasma concentration. Finally, the potential advantage of a punctual screening during long-term treatment has not been investigated.

A number of target-specific oral anticoagulants (TSOAs) have been developed in recent years, and some have shown considerable promise in large-scale, randomized clinical trials in the prevention and treatment of thromboembolism. Unlike traditional anticoagulants, such as vitamin K antagonists, these TSOAs exhibit predictable pharmacokinetics and pharmacodynamics. Among these agents, rivaroxaban, a direct Factor Xa inhibitor, has been approved for clinical use in many countries for the management of several thromboembolic disorders. As with the other TSOAs, rivaroxaban is given at fixed doses without routine coagulation monitoring. However, in certain patient populations or special clinical circumstances, measurement of drug exposure may be useful, such as in suspected overdose, in patients with a haemorrhagic or thromboembolic event during treatment with an anticoagulant, in those with acute renal failure, or in patients who require urgent surgery. This article summarizes the influence of rivaroxaban on commonly used coagulation assays and provides practical guidance on laboratory testing of rivaroxaban in routine practice. Both quantitative measurement (using the anti-Factor Xa method) and qualitative measurement (using prothrombin time, expressed in seconds) are discussed, together with some practical considerations when performing these tests and interpreting the test results.

New oral anticoagulants are directed towards a single target, essentially factor Xa (FXa) or factor IIa. They do not require routine coagulation monitoring. However, in special clinical settings (emergency surgery, bleeding, thrombosis, control of the patient's compliance, suspected overdose, potential drug interference, and so on), measurement of plasma levels is needed. Several available anti-FXa assays are used for monitoring anticoagulant activity of heparins and fondaparinux. They must be modified and standardized for the measurement of direct FXa inhibitors (rivaroxaban, apixaban, edoxaban, betrixaban and others). The use of calibrators (lyophilized plasma with a known concentration of drug) allows an expression of the results in ng per ml of plasma. Two categories of assays - endogenous and exogenous assays are available. Endogenous assays are useful in pharmaceutical research, while exogenous assays are used in clinical laboratories. The preferred anti-FXa assay is a specific method in contrast to prothrombin time and activated partial thromboplastin time, but it is not available everywhere at any time. A specific measurement of direct FXa inhibitors is feasible with the use of a new test developed by the authors' group. The physicians must be aware of the possibility to measure the plasma concentration of FXa inhibitors in patients at high risk of bleeding and in several other special clinical situations.

SummaryThe EXCLAIM study enrolled hospitalised acutely ill medical patients with age >40 years and recently-reduced mobility into a trial of extended-duration anticoagulant thromboprophylaxis. This post-hoc analysis evaluated the impact of age on patient outcomes. After completion of open-label therapy with enoxaparin 40 mg once-daily (10 ± 4 days), eligible patients underwent randomisation to receive double-blind therapy of enoxaparin (n=2,975) or placebo (n=2,988) for 28 ± 4 days. During follow-up, the venous thromboembolism (VTE) risk increased with age in both treatment groups. In patients with age >75 years, those who received extended-duration enoxaparin had lower incidence of VTE (2.5% vs 6.7%; absolute difference [AD] [95% confidence interval]: −4.2% [−6.5, −2.0]), proximal deep-vein thrombosis (2.5% vs 6.6%; AD −4.1 % [−6.2, −2.0]), and symptomatic VTE (0.3% vs 1.5%; AD −1.2% [−2.2, −0.3]), in comparison to those who received placebo. In patients with age ≤75 years, those who received enoxaparin had reduced VTE (2.4% vs 2.8%; AD −0.4% [−1.5, 0.7]) and symptomatic VTE (0.2% vs 0.7%; AD −0.6% [−1.0, −0.1]) in comparison to those who received placebo. In both age subgroups, patients who received enoxaparin had increased rates of major bleeding versus those who received placebo: age >75 years (0.6% vs 0.2%; AD +0.3% [−0.2, 0.9], respectively); age ≤75 years (0.7% vs 0.2%; AD +0.5% [0.1, 0.9]). Patients in both age subgroups that received enoxaparin had similar low bleeding rates (0.6% and 0.7%, respectively). VTE risk increased with age, though the bleeding risk did not. Patients with age >75 years had a more favourable benefit-to-harm profile than younger patients.

Introduction Edoxaban, an oral direct factor Xa (FXa) inhibitor, is in Phase III development for prevention and treatment of thromboembolic disorders. Fondaparinux is an approved indirect FXa inhibitor. This study compared the effects of edoxaban and fondaparinux on thrombin generation (TG) using the calibrated automated thrombogram (CAT). Secondary objectives included evaluation of edoxaban and inhibition of coagulation parameters (prothrombin time [PT], activated partial thromboplastin time [aPTT]), anti-FXa activity and clotting times. Materials and Methods Pooled citrated platelet-poor plasma from healthy subjects was spiked with edoxaban (0.02-3.65 μM) or fondaparinux (0.15-1.18 μM). Parameters of TG were calculated using Thrombinoscope™ software. PT ratios and aPTT were measured in the presence of different thromboplastin reagents. Exogenous anti-FXa was measured using Rotachrom HBPM (Stago) and a specific assay developed for direct FXa inhibitors (Hyphen BioMed). Results Edoxaban exhibited a 3-fold greater concentration-dependent effect than fondaparinux across TG parameters (except endogenous thrombin potential). Edoxaban also produced a concentration-dependent prolongation of PT ratio and aPTT. The magnitude of concentration-dependent increase was related to thromboplastin reagent. In contrast to edoxaban, fondaparinux was inactive on these clotting tests. Linear correlations were observed between plasma concentration of edoxaban and anti-FXa activity and results of clotting time assays. Conclusions TG evaluation by the CAT method, coagulation tests, and anti-FXa and clotting assays demonstrated concentration-dependent effects of edoxaban. The PT and aPTT prolongation are reagent dependent; correction of PT ratio by international normalized ratio does not reduce variability in response. The greater effect of edoxaban vs. fondaparinux may be related to the broader activity of direct FXa inhibitors compared with indirect FXa inhibitors.

Elderly people with renal impairment are at high risk for venous thromboembolism (VTE) and acute coronary syndromes (ACS); however, they are also at increased risk for bleeding complications. Evidence-based data for the management of anticoagulation in elderly patients with severe renal impairment, in particular, are limited. These patients are frequently excluded from randomized clinical trials evaluating anticoagulants, confounding clinical decision making. Low-molecular-weight heparins (LMWHs), such as enoxaparin sodium and dalteparin sodium, provide a predictable anticoagulant effect across almost all patient populations; however, because they are primarily eliminated through the kidneys, elderly patients with moderate or severe renal impairment are potentially at risk for LMWH accumulation. Clinical evidence suggests that treatment with full-dose enoxaparin sodium could increase the risk for bleeding in elderly patients with severe renal impairment; however, this risk is ameliorated with approved dose adjustments. Dalteparin sodium has been evaluated in small studies within this population but no strategy for reduced dosing has been developed. There are limited clinical data on the use of fondaparinux sodium and, in particular, the new anticoagulants, such as dabigatran etexilate and rivaroxaban, in elderly patients with renal impairment. Evidence suggests that the clearance of fondaparinux sodium is mildly reduced in elderly patients, and more substantially reduced in patients with severe renal impairment; a dose reduction has recently been approved in Europe. Age and renal function appear to affect the exposure of dabigatran etexilate. A dose reduction is recommended in the elderly and in those with moderate renal function, but dabigatran etexilate is contraindicated in severe renal impairment. Rivaroxaban has been associated with increased exposure and pharmacodynamic effects in the elderly and those with renal impairment; at present there is no facility for dose reduction. Monitoring anticoagulant activity may help improve the safety profile of anticoagulants in elderly patients with renal impairment, particularly when approved dose reductions are unavailable. However, unlike the LMWHs, clinical surveillance of the new anticoagulants is challenging. In conclusion, extra care should be taken when anticoagulants are administered to elderly patients with renal impairment. Additional data are needed, particularly for the new anticoagulants, in order to guide the prevention and treatment of VTE and ACS, and to ensure the optimal safety profile in older patients with renal impairment.

SummaryEdoxaban, an oral direct factor Xa (FXa) inhibitor, is in phase III clinical development for stroke prevention in atrial fibrillation and treatment of venous thromboembolism. The shed blood model allows for study of activated coagulation at a site of standardised tissue injury due to local release of tissue factor. The objective of this study was to evaluate the effect of three doses of edoxaban on markers of coagulation in shed and venous blood versus placebo and a standard prophylactic dose of fondaparinux. A total of 100 healthy male subjects were randomised to receive single doses of one of five treatments: subcutaneously administered fondaparinux 2.5 mg; orally administered edoxaban 30, 60, or 120 mg; or placebo. The primary objective was measurement of blood coagulation markers prothrombin fragment 1+2 (F1+2) and thrombinantithrombin (TAT) complex, and platelet activation marker β-thromboglobulin (β-TG), in venous and shed blood. Secondary objectives included pharmacokinetics, shed blood volume, and safety of edoxaban. Single doses of edoxaban caused rapid and significant decreases of F1+2, TAT, and β-TG in the shed blood model, indicating inhibition of thrombin generation and platelet activation. Inhibition was significantly less for fondaparinux versus edoxaban. Baseline-corrected F1+2, TAT, and β-TG values demonstrated sustained inhibition up to 24 hours for shed blood in the edoxaban groups but no significant inhibition in venous blood. Overall, edoxaban treatments were well tolerated. In conclusion, single oral doses of edoxaban 30, 60, or 120 mg caused rapid and sustained inhibition of coagulation up to 24 hours in the shed blood model.

Several new oral anticoagulants such as rivaroxaban (which targets Factor Xa) and dabigatran etexilate (which targets thrombin) are in advanced stages of clinical development and are already available for clinical use in some countries. Although these agents do not require routine coagulation monitoring, assays to assess the level of anticoagulation may be of assistance in certain circumstances such as in case of overdose, in patients with a hemorrhagic or thromboembolic event during treatment, or to assess compliance. Moreover, the influence of the new oral anticoagulants on routine coagulation tests must be recognized. The prothrombin time is not suitable for rivaroxaban measurement for several reasons, and the routinely used international normalized ratio for monitoring the vitamin K antagonists cannot be applied to rivaroxaban. Development of universal assays is challenging because the new oral anticoagulants have different targets, and even those with the same target have variable effects on routine coagulation assays. Focusing on rivaroxaban, there is emerging evidence that an anti-Factor Xa assay that uses rivaroxaban-containing plasma calibrators may provide the optimal method for determining plasma rivaroxaban concentrations.

Introduction Edoxaban (the free base of DU-176b) is a new, oral direct Factor Xa inhibitor. This is the first study to compare the hemostatic response to edoxaban, ximelagatran, and dalteparin in healthy, elderly adults. Materials and Methods In this open-label, active-controlled clinical trial, 40 adults (65-75 years), were randomised to: oral edoxaban (60 mg, twice-daily, 7 doses), subcutaneous dalteparin (5000 IU, once-daily, 4 doses), oral ximelagatran (24 mg, twice-daily, 7 doses) or no drug. Blood samples were taken before, and 1.5, 4, 12, 24, 72, 84, 96, 108, 120, and 144 hours after, the first dose. The primary outcomes were changes in thrombin-antithrombin complex, prothrombin fragment 1 + 2 and D-dimer, and adverse events. Additional biomarkers of coagulation, and endothelial cell and platelet activation were compared (ANOVA). Results All subjects completed the study. Inhibition of thrombin generation lag time, peak, and constant velocity index were significantly greater, and extended for a longer period of time, following edoxaban administration, compared with dalteparin. We found that the traditional assay for anti-FXa activity was not appropriate for the new anticoagulants. Biomarker changes following edoxaban administration (including prolongation of prothrombin time) reflected inhibition of Factor Xa; there was no effect on platelet, tissue factor or endothelial activation. There were no clinically significant changes in primary outcomes. No serious adverse events were reported. Conclusion Oral administration of edoxaban resulted in effective Factor Xa and TG inhibition, and was well-tolerated. Studies are needed to confirm edoxaban (60 mg daily) use in clinical practice. Sponsorship Daiichi Sankyo Pharma Development.

The endothelium is recognized today as a functional and dynamic component of the body that plays an important part in health and disease. This article briefly reviews the role of endothelium in thrombosis and hemostasis. There is a paradigm shift from one that regards the endothelium as one single entity to the concept that the endothelium is heterogeneous. Thrombotic complications in many disorders show a predilection to specific locations, despite the fact that a hypercoagulable state affects the entire body. Likewise, bleeding is more commonly encountered in certain anatomical locations than in others. Recent observations of the heterogeneous distribution of coagulation and fibrinolytic factors in the endothelium and the adaptation of the endothelium to various stimuli may provide an explanation for the diverse phenotypes. Recognition of this changing paradigm is helpful to for the diagnosis and management of bleeding and thrombotic complications. It also helps in the understanding of the pathogenesis of many bleeding and thrombotic disorders, and in the development of new drug designs for site-specific therapy.

SummaryIn the US, ambulatory status is often a criterion for stopping prophylaxis for venous thromboembolism (VTE). In an analysis of the prophylaxis in MEDical patients with ENOXaparin (MEDENOX) trial, ambulatory status was assessed as outcome and patients grouped accordingly for further analysis. Rates of VTE and bleeding were evaluated. Using multivariate logistic regression, the relationships between thromboprophylaxis, VTE risk, and ambulatory status were assessed. Ambulatory status was reached in 607/1,084 patients, in a mean time of 4.4 days. Thromboprophylaxis was provided for 7.3 and 7.7 days in the ambulatory and non-ambulatory groups. Although VTE rates were lower in ambulatory patients, enoxaparin 40 mg once daily significantly reduced the risk of VTE vs. placebo in ambulatory (3.3% vs. 10.6%; relative risk [RR] = 0.31; 95% confidence interval [CI], 0.13ﺹ0.78; p=0.008) and non-ambulatory patients (9.0% vs. 19.7%; RR = 0.46; 95% CI, 0.23ﺹ0.91; p=0.02). Major bleeding was not significantly different between enoxaparin and placebo in either group. By multivariate regression analysis, VTE risk in ambulatory patients was lower with enoxaparin vs. placebo (odds ratio [OR] = 0.28; 95% CI, 0.11ﺹ0.74; p=0.01), but higher in patients with a history of VTE (OR = 3.74; 95% CI, 1.59ﺹ8.84; p=0.003) or cancer (OR = 2.12; 95% CI, 1.00ﺹ4.48; p=0.049). Despite timely mobilisation, patients who become ambulatory are at VTE risk and experience a significant risk reduction with enoxaparin 40 mg. Therefore, it is essential that ambulatory patients receive recommended thromboprophylaxis.

Auteur(s) : Meyer Michel Samama Service d’hematologie biologique, AP-HP Hotel-Dieu, 1, place du Parvis-Notre-Dame, 75181 Paris cedex 04, France La prophylaxie de la maladie thromboembolique veineuse (MTEV) gagne une place de plus en plus importante dans le milieu medical et chirurgical, depuis que de nombreuses etudes ont bien etabli son efficacite et sa securite. Tous les specialistes recommandent de choisir et d’adapter le traitement prophylactique en fonction de l’importance [...]

The procoagulant activity of a thrombus is essentially due to clot-associated factor IIa and factor Xa activities.The aim of this review is to underline that specific antithrombin and anti-Xa drugs, such as r-hirudin and DX 9065a, respectively, are complementary, and could be used in combination in clinical trials in patients with acute arterial thrombosis such as coronary syndromes. After standardization of the in-vitro techniques for clot-bound thrombin and clot-associated factor Xa, we have studied the anticoagulant effect of unfractionated heparin and a low-molecular heparin in an in-vitro model. We have confirmed the inability of heparins to inhibit clot-bound thrombin and clot-associated factor Xa. We have compared r-hirudin, a direct thrombin inhibitor, with DX9065a, a direct factor Xa inhibitor. We have observed that r-hirudin inhibited clot-bound thrombin but not clot-bound factor Xa. After r-hirudin treatment interruption, a hypercoagulation rebound has been reported and it could be in relation with the persistence of factor Xa activity in the clot. We have demonstrated that DX9065a inhibits clot-bound factor Xa but does not inhibit clot-bound factor IIa. The complementary effect of DX9065a and r-hirudin is demonstrated in this experimental model. It is likely that several other combinations of drugs may also exhibit an increase of the antithrombotic activity which could be of interest in clinical implication for the treatment of several groups of patients at high risk of arterial thrombosis.

Argatroban, a synthetic chemical compound, and recombinant hirudin (r-hirudin) are both direct thrombin inhibitors. Their actions are reversible and irreversible, respectively. We studied the influence of these two anticoagulants on the thrombin generation test using the method according to Hemker. For this investigation, a pool of citrated, platelet-poor, normal human plasma was supplemented with each drug at increasing concentrations. r-Hirudin had a dramatic influence on the initiation phase with almost no effect on the peak thrombin generated or the endogenous thrombin potential (ETP). In contrast, argatroban prolonged the initiation phase of thrombin generation and decreased the peak and ETP values. These differences are attributable to the irreversible and reversible binding to thrombin of these agents. This study reveals clear distinctions between the mechanisms of these two thrombin inhibitors.

This chapter describes the pharmacology of approved parenteral anticoagulants, including the indirect anticoagulants, unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs), fondaparinux, and danaparoid as well as the direct thrombin inhibitors hirudin, bivalirudin, and argatroban. UFH is a heterogeneous mixture of glycosaminoglycans that bind to antithrombin via a unique pentasaccharide sequence and catalyze the inactivation of thrombin factor Xa and other clotting factors. Heparin also binds to cells and other plasma proteins, endowing it with unpredictable pharmacokinetic and pharmacodynamic properties, and can lead to nonhemorrhagic side effects, such as heparin-induced thrombocytopenia (HIT) and osteoporosis. LMWHs have greater inhibitory activity against factor Xa than thrombin and exhibit less binding to cells and proteins than heparin. Consequently, LMWH preparations have more predictable pharmacokinetic and pharmacodynamic properties, have a longer half-life than heparin, and have a lower risk of nonhemorrhagic side effects. LMWHs can be administered once or twice daily by subcutaneous injection, without anticoagulant monitoring. Based on their greater convenience, LMWHs have replaced UFH for many clinical indications. Fondaparinux, a synthetic pentasaccharide, catalyzes the inhibition of factor Xa, but not thrombin, in an antithrombin-dependent fashion. Fondaparinux binds only to antithrombin; therefore, HIT and osteoporosis are unlikely to occur. Fondaparinux has excellent bioavailability when administered subcutaneously, has a longer half-life than LMWHs, and is given once daily by subcutaneous injection in fixed doses, without anticoagulant monitoring. Three parenteral direct thrombin inhibitors and danaparoid are approved as alternatives to heparin in HIT patients.

This chapter focuses on new antithrombotic drugs that are in phase II or III clinical testing. Development of these new agents was prompted by limitations of existing antiplatelet, anticoagulant, or fibrinolytic drugs. Addressing these unmet needs, this chapter (1) outlines the rationale for development of new antithrombotic agents, (2) describes the new antiplatelet, anticoagulant, and fibrinolytic drugs, and (3) provides clinical perspectives on the opportunities and challenges faced by these novel agents.

Congenital afibrinogenemia is a rare disorder characterized by the absence in circulating fibrinogen, a hexamer composed of two sets of three polypeptides (Aalpha, Bbeta and gamma). Although predisposition to thrombosis is a well known feature of dysfibrinogenemia, the relatively frequent thrombotic manifestations seen in congenital afibrinogenemia are puzzling. We herein report a mutational analysis of a young afibrinogenemic man from Turkey with multiple thrombo-embolic events involving both arteries and veins. Purified DNAs of the propositus was used for amplification by polymerase chain reaction of all the exons of the A subunit gene with primers allowing the analysis of the intron-exon boundaries. Analysis of the genes coding for the three fibrinogen chains of the propositus found a homozygous G to A transition in the exon 5 of the A alpha chain gene (g.g4277a; access number gi458553). The TGG to TGA codon change predicts a homozygous W315X in the A alpha chain (p.W334X when referring to the translation initiation codon). Both parents and his brother were found to carry this heterozygous mutation. This is the first report of a patient homozygous for this rare mutation associated with afibrinogenemia. Our patient was free of known risk factors as well as diseases associated with thrombosis including atherosclerosis, vasculitis, Buerger's disease, and it seems therefore probable that afibrinogenemia itself might have contributed to both arterial and venous thrombosis.

Summary. Background: Low-molecular-weight heparins (LMWHs), derived from unfractionated heparin (UFH) by different depolymerization procedures, vary in both their relative abilities to enhance the inhibition of FXa (anti-FXa) and thrombin (anti-FIIa), and in their physicochemical properties. Objective: We aimed to profile the inhibition of thrombin generation induced by bemiparin, enoxaparin, nadroparin, dalteparin and tinzaparin in platelet-rich plasma (PRP), and to compare them with UFH and fondaparinux (a synthetic pentasaccharide that specifically enhances FXa inhibition). Methods: Different LMWHs, UFH or fondaparinux were added to normal PRP. Thereafter, tissue factor-triggered thrombin generation was assessed using the Thrombogram–Thrombinoscope® assay. Results: At equivalent anti-FIIa activity concentrations, LMWHs and UFH exhibited similar inhibitory effects upon thrombin generation. However, when used at equivalent anti-FXa activity concentrations, tinzaparin was significantly more active than the other LMWHs at inhibiting thrombin generation, and had similar activity to that of UFH. Enoxaparin, nadroparin and dalteparin all showed similar inhibitory activities. In these experiments, bemiparin exhibited the lowest inhibitory effect on thrombin generation of all the LMWHs. At 0.1 μg mL–1 (0.093 anti-FXa IU mL–1), fondaparinux inhibited the rate of thrombin generation by 50%. A 7-fold higher concentration of fondaparinux was required to inhibit the endogenous thrombin potential by 50%. Conclusions: LMWHs have a variable inhibitory effect on thrombin generation in vitro when compared by anti-FXa activity, but are similar when compared by their anti-FIIa activities. The rate of thrombin generation during the propagation phase, rather than the endogenous thrombin potential, is more sensitive to the anticoagulant activity of fondaparinux and the polysaccharide chains of LMWHs possessing only anti-FXa activity.

SummaryVenous thromboembolism (VTE) is often asymptomatic, misdiagnosed, and unrecognized at death, and there is a lack of routine postmortem examinations. These factors are thought to result in marked underestimates ofVTE incidence. The objective of our study was to estimate the total burden of VTE within the European Union (EU) per annum. An epidemiological model was constructed to estimate the number of community- and hospital-acquired incidents and recurrent cases (attack rate) of nonfatal VTE and VTE-related deaths, as well as incident and prevalent cases of post-thrombotic syndrome (PTS) and chronic thromboembolic pulmonary hypertension (PH) occurring in the EU per annum. Individual models were developed for six EU countries. The models were populated with data from published literature and, where necessary, expert opinions. The findings were tested using probabilistic sensitivity analyses. The esti mated total number of symptomaticVTE events (range based on probabilistic sensitivity analysis) per annum within the six EU countries was 465,715 (404,664–538,189) cases of deep-vein thrombosis, 295,982 (242,450–360,363) cases of pulmonary embolism (PE), and 370,012 (300,193–483,108) VTE-related deaths. Of these deaths, an estimated 27,473 (7%) were diagnosed as being antemortem; 126,145 (34%) were sudden fatal PE, and 217,394 (59%) followed undiagnosed PE. Almost threequarters of all VTE-related deaths were from hospital-acquired VTE.VTE is a major health problem in the EU, with over one million VTE events or deaths per annum in the six countries examined. Given the availability of effective VTE prophylaxis, many of these events and deaths could have been prevented. These results have important implications for the allocation of healthcare resources.

Background Aspirin (ASA) failure to inhibit in vitro platelet function had been termed ASA resistance. The prevalence of this phenomenon as measured with different platelet function tests varies widely among studies. Objectives In this study, we propose to determine the prevalence of ASA non-responsiveness in stable coronary artery patients using three different tests. Patients and methods One hundred ninety-one patients with a stable coronary artery disease and receiving secondary ASA prophylaxis (250 mg/day) were tested. For each patient the ASA-induced platelet inhibition was determined using three different tests: Ivy Bleeding time (BT), collagen/epinephrine closure time (CEPI-CT; PFA-100™, Dade-Behring) and urinary 11-dehydrothromboxane B2 (uTxB2) excretion level. The agreement between these tests was evaluated by kappa statistics test. Results The prevalence of biological ASA resistance was 15.7% (n = 30), 20.4% (n = 39) and 24.6% (n = 47) by BT, PFA-100™ and UTxB2, respectively. Only fourteen patients (7.3%) were non-responders for two tests: 6 (3.1%) BT/ PFA-100™; 1 (0.5%) BT/UTxB2; 7 (3.7%) PFA-100™/UTxB2). A poor agreement was found between these three methods and only 3 patients were resistant with all the tests (1.6%). Conclusion The lack of agreement supposed that different types of aspirin resistance exist. Thus, combination of two tests or more could be a primary solution for a better identification of ASA resistant patients. This hypothesis must be confirmed by a large-scale randomized study with clinically well-defined endpoints.

Cancer is linked with hypercoagulability and risk of thrombosis and this close association was recognized by Armand Trousseau in 1865. The relation between cancer and blood coagulation is reciprocal: cancer induces a hypercoagulable state and predisposes to thrombosis and activation of platelets, blood coagulation and fibrinolysis interfere with tumor cell biology, tumor growth, angiogenesis and metastatic process. In the present article, we analyze the clinical trials which assessed the influence of anticoagulant treatment on the survival of patients with cancer. The available data show that low-molecular-weight heparins (LMWHs) tend to be more effective and safer than vitamin K antagonists (VKA) in improving survival in patients with cancer. The beneficial effect of anticoagulation with either LMWHs or VKA is not universal for all patients with cancer. There are some histological types of cancers which, at early stages, appear to be more sensitive than others to the effect of anticoagulant treatment. The available clinical trials, although limited, are encouraging for the beneficial effect of anticoagulant treatment on the survival of cancer patients. More clinical trials are needed, targeting groups of patients homogenous regarding the type of cancer, the stage of the disease and life expectancy. The forthcoming clinical trials have to address some issues regarding the optimal dose, the timing and the duration of treatment with LMWH in relation to chemotherapy or other anticancer therapies.

Non-VKA oral anticoagulants (NOACs), thanks to their ease of use and their similar or superior safety/efficacy profiles versus warfarin, have now widely reached the lucrative market of anticoagulation. However, while the marketing authorization holders always claim, in a quite unclear way that no monitoring is required, accumulative evidence and cases of major bleeding have been described in the literature and reported by spontaneous reporting systems at the regulator's level. These compounds are usually given at fixed doses without routine coagulation monitoring. However, new data suggests that an assessment of the response at the individual level could improve the benefit-risk ratio of, at least dabigatran. Therefore, in certain patient populations, i.e. acute or chronic renal impairment or multiple drug interactions, measurement of drug exposure may be useful to ensure an optimal treatment response. More specific circumstances such as patients experiencing a haemorrhagic or thromboembolic event during the treatment duration, patients who require urgent surgery or an invasive procedure, or patient with a suspected overdose could benefit from such a measurement. This article aims at providing guidance on how to best estimate the intensity of anticoagulation using laboratory assays in daily practice.

RESUME Le risque d’evenements thromboemboliques chez la femme enceinte porteuse d’une thrombophilie hereditaire avec mutation heterozygote du FV Leiden, du FII 20210A ou des deux, est mal documente. Aussi, les protocoles prophylactiques sont-ils encore discutes. Une etude retrospective a ete conduite chez 208 femmes porteuses d’une thrombophilie hereditaire par mutation heterozygote du FV ou du FII ou des deux. Le nombre total de grossesses menees a terme etait de 406 dont 10 avec prophylaxie antithrombotique. La frequence des evenements thrombotiques ante- et post-partum etait significativement plus grande dans le groupe de femmes ayant les 2 alterations genetiques (17,8%) que dans le groupe ou seul le gene du FII etait mute (6,2%) p = 0.003. En revanche, il n’existait pas de difference significative entre le groupe FV+FII et le groupe FV seul (10%). Le risque veineux lie a l’association de ces 2 varietes les plus communes de thrombophilie constitutionnelle est donc plutot additif que multiplicatif. Neanmoins, la presence d’un antecedent thromboembolique avant la grossesse dans ce groupe FV+FII majorait considerablement le risque thromboembolique (50%). La frequence des accidents a ete plus grande dans le post-partum que dans l’ante-partum. Il n’a pas ete observe de difference significative sur la frequence des pertes foetales dans ces 3 groupes, mais cet evenement n’etait pas un critere de jugement primaire dans cette etude. Ces resultats, recueillis dans un seul centre, permettent de proposer une attitude pour la prophylaxie des accidents chez les 3 groupes de femmes. L’utilisation systematique d’une HBPM n’est pas indiquee pendant la grossesse chez les femmes asymptomatiques ayant une seule mutation. En revanche, elle est justifiee pendant toute la grossesse chez les femmes ayant les 2 mutations et des antecedents de thrombose. Chez celles qui n’ont pas d’antecedent, une prophylaxie pendant une partie ou toute la grossesse doit etre consideree et decidee au cas par cas. Dans la periode du post-partum, une attitude consensuelle recommande un traitement prophylactique systematique avec une HBPM pendant 6 semaines au moins, dans toutes les thrombophilies hereditaires : anomalies isolees et combinees.

This article about new anticoagulant drugs is part of the seventh American College of Chest Physicians Conference on Antithrombotic and Thrombolytic Therapy: Evidence-Based Guidelines. The limitations of existing oral and parenteral anticoagulant agents have prompted a search for novel agents. Focusing on new anticoagulant drugs for the prevention and treatment of arterial and venous thrombosis, this article (1) reviews arterial and venous thrombogenesis, (2) discusses the regulation of coagulation, (3) describes the pathways for testing new anticoagulant agents, (4) describes new anticoagulant strategies focusing primarily on agents in phase II or III clinical testing, and (5) provides clinical perspective as to which of these new strategies is most likely to succeed.

Purpose of review Venous thromboembolism is a multifactorial silent disease and tends not to be suspected by physicians, especially in medical patients. Pulmonary embolism is the most preventable cause of death among hospitalized patients. It is of major importance to assess the risk for venous thromboembolism and to adapt the prophylactic strategy with the aim of improving the risk-benefit ratio of the prophylaxis. Recent findings Prophylaxis of venous thromboembolism can be done by either mechanical means or pharmacologic agents or both. The Medenox trial, the Prime study, the Prince study, the Prevent study, and the Artemis trial demonstrated that acutely ill medical patients are at increased risk of venous thromboembolism and that low molecular weight heparins (enoxaparin 40 mg or dalteparin 5000 IU subcutaneously once daily for 10 days) as well as fondaparinux 2,5 mg subcutaneously once daily for 10 days have a favorable risk-benefit ratio in the prevention of venous thromboembolism in acutely ill medical patients. The publication of the results of the Exclaim study is expected to clarify the optimal duration of prophylaxis in this group of patients. Patients hospitalized in medical intensive care units as well as patients with active cancer or central venous catheters are at increased risk of venous thromboembolism, and the studies published so far demonstrate the favorable risk-benefit ratio of thromboprophylaxis with either low molecular weight heparins or low-dose warfarin. Summary Acutely ill medical patients are at increased risk of venous thromboembolism. Prophylaxis with low molecular weight heparins and fondaparinux is effective and safe. Initiatives to improve venous thromboembolism prophylaxis should be based on the education of physicians regarding the individualized risk assessment.

We have developed an in vitro protocol for the measurement of clot-bound thrombin. This protocol uses a chromogenic substrate for thrombin and a microtiter plate reader and is suitable for screening inhibitors for thrombin that are directed to clot-bound thrombin. Clots were obtained after recalcification of human plasma. For the measurement of clot-bound thrombin, we read the optical density (OD) at 405 nm on a spectrophotometer and compared the results to that obtained with a standard curve of human alpha thrombin. We stopped the amidolytic reaction at 10 min because the optical density was linear until 20 min under our experimental conditions. We suggest that clot-bound thrombin can be measured using a chromogenic substrate specific for thrombin under our experimental condition.

SummaryFondaparinux (Arixtra®), a specific AT-dependent FXa inhibitor, is effective and safe in the prevention and treatment of venous thromboembolism, but some major hemorrhagic events may occur. No specific antidote to fondaparinux has been proposed. Recombinant FVIIa (Novoseven®) could be used as an haemostatic treatment, but this option has not been well documented. We studied the effect of rFVIIa (1 µg/ml) on the inhibition of thrombin generation induced by fondaparinux (0.1µg/ml to 1 µg/ml). Coagulation was triggered in platelet rich plasma (PRP) or in whole blood by recalcification in the presence of diluted thromboplastin. In PRP thrombin generation was assessed using the thrombinoscope assay. In whole blood, prothrombin activation was assessed by measuring the kinetics of F1+2 formation using an ELISA assay. Fondaparinux at concentrations equal or greater than 0.5 µg/ml prolonged the initiation phase of thrombin generation, and reduced the velocity of prothrombin activation. It also decreased by 60% the endogenous thrombin potential. In the presence of fondaparinux (0.5 µg/ml to 1 µg/ml) rFVIIa accelerated the initiation phase of thrombin generation, but it did not significantly increase the endogenous thrombin potential. However, rFVIIa did not completely reverse the inhibitory effect of fondaparinux on the parameters of thrombin generation and prothrombin activation. This study shows that rFVIIa accelerates thrombin generation, but does not completely reverse the inhibitory effect of fondaparinux on thrombin generation. The potential clinical use of rFVIIa as haemostatic treatment of major bleedings related to fondaparinux has to be evaluated.

The in vitro closure time (CT), determined by the Platelet Function Analyzer (PFA-100), is used to monitor patients treated with aspirin. A relatively high percentage of in vitro aspirin resistance was reported despite an adequate inhibition of platelet response to arachidonic acid and we investigated whether high plasma levels of von Willebrand factor ristocetin cofactor activity (vWF:RCo) may contribute to this profile. Platelet aggregation test, CT [collagen adrenaline (CEPI-CT) and collagen adenosine 5'-diphosphate (ADP) (CADP-CT)], and vWF:RCo levels were evaluated in 55 consecutive patients receiving aspirin (75-250 mg/d) versus 32 untreated control subjects. All the aspirin-treated patients showed platelet aggregation responses that reflected the aspirin intake. However, CT data analysis enabled aspirin good-responder (GR) and aspirin bad-responder (BR) patients to be identified. All GR group subjects (n = 27), had a CEPI-CT and a CADP-CT longer than 300 s and 96 s respectively. The BR group (n = 28) had CEPI-CT values below 200 s and all CADP-CT were in the normal range (77 +/- 19 s). Interestingly, the BR plasma vWF:RCo levels were significantly higher (159 +/- 43%) than those of the GR group (121 +/- 34%) (P < 0.01), which were similar to control values (114 +/- 31%). A negative correlation between vWF:RCo and CT values was established. We demonstrate that in vitro aspirin-resistance, revealed by PFA-100 CT prolongation failure, is correlated to increased plasmatic vWF:RCo levels, reinforcing its particular importance in PFA-100 cartridges performance.

The risk of venous thromboembolism (VTE) in the absence of prophylaxis was evaluated in a retrospective study of 47 women (84 pregnancies) with combined thrombophilia [heterozygous factor V Leiden (FVL) plus prothrombin (FII) 20210A mutation (group I)] and in 82 women (193 pregnancies) with the FII alone (group II). VTE was more frequent in group I than in group II [17.8% versus 6.2%, P = 0.003, relative risk (RR) 2.9, 95% confidence interval (CI) 1.4-5.9], ante partum (7.1% and 2.1%) and post partum (11.5% and 4.2%). The risk was higher in index cases than in family members (RR 2.5, 95% CI 1.2-5.2 and RR 2.1, 95% CI 0.2-22.3 respectively) Even women who had no history of VTE before pregnancy had an increased risk (RR 2.2, 95% CI 1.0-4.8). Our results suggest that, during ante partum, prophylaxis is indicated in women with combined thrombophilia and with a VTE before pregnancy. In those without VTE before pregnancy, prophylaxis might be decided for each individual case, taking into consideration all risk factors. In women with the FII mutation alone, the low risk may not justify prophylaxis in the absence of previous VTE. In post partum, prophylaxis is indicated in all cases.

The tissue factor (TF) pathway is preponderant in the initiation of blood coagulation in normal haemostasis and in thrombotic states. In the present study we investigated the mechanisms by which the synthetic pentasaccharide may influence the regulation of the TF pathway during clotting of human platelet poor plasma (PPP). Clotting of normal PPP or plasmas immuno-depleted of a single clotting factor (factor VII, factor XII, factor XI, factor IX, factor VIII, factor X, factor V, factor II) was initiated by triggering the TF pathway in the presence of fondaparinux (0.5 microg/ml). Activated factor VII (FVIIa) levels were measured in serum obtained at several time intervals after re-calcification of PPP. A clotting assay highly specific for FVIIa was used. The synthetic pentasaccharide inhibited the generation of FVIIa by 66%. The inhibitory effect of fondaparinux on FVIIa was completely abolished when antithrombin activity of plasma was inhibited by a specific antibody. Following the activation of TF pathway in plasmas depleted of factor X or factor IX, the inhibitory effect of fondaparinux on FVIIa generation was completely abolished, whereas it was not significantly modified when the other clotting factor-depleted plasmas were clotted. When fondaparinux was added in the serum, after the maximal generation of FVIIa, it inhibited by 20-30% the activity of the FVIIa-TF complex. These data suggest that fondaparinux enhances the antithrombin-dependent downregulation of the TF pathway by decreasing the generation of FVIIa via the inhibition of the generation and the activity of activated factor IX and activated factor X, and by inhibiting the activity of the FVIIa-TF complex.

Summary. Factor VIIa (FVIIa) and thrombin generation occur in patients suffering an acute coronary event. We studied the effect of treatment with enoxaparin on FVIIa and prothrombin activation in patients with unstable angina. Anti-Xa activity, FVIIa, FVII coagulant activity (FVII:C) and FVII antigen (FVII:Ag), free tissue factor pathway inhibitor (TFPI), and prothrombin fragments 1 + 2 (F1+2) were measured in patients' plasma, over a 24-h treatment period with enoxaparin. All 14 patients recruited in the study (mean age 68 years) were treated with a subcutaneous injection of enoxaparin, 1 mg/kg twice daily. Blood was drawn just before, and at different time intervals after, the first injection. Before enoxaparin administration, the levels of FVIIa (4·02 ± 0·8 ng/ml) and F1+2 (2·68 ± 0·2 nmol/l) were significantly increased as compared with control subjects (2·3 ± 0·3 ng/ml and 0·9 ± 0·1 nmol/l respectively, P

Inherited thrombophilias are associated with an increased risk of venous thromboembolism (VTE) and the risk is further increased during pregnancy. However, not all pregnancies or all thrombophilias carry the same risk. Deficiencies in coagulation inhibitors and especially in antithrombin are rare but are associated with a higher risk than the most frequent factor V Leiden or prothrombin (factor II) 20210A mutations. Differences may be observed depending on heterozygosity or homozygosity of the defects and on the presence of combined thrombophilias. Although we now have more information on the global risk of thrombosis in thrombophilia, the magnitude of the risk is unknown in women who do or do not have a history of VTE, and in those who are the propositus or family members. Additional risk factors may be taken into account such as age of the mother, cesarean section, obesity, and immobilization during pregnancy. Recommendations of the American College of Chest Physicians (ACCP) concerning prophylaxis during pregnancy published in 2001 are mostly 1C recommendations; they are based on observational studies and subject to changes when more information becomes available. There is now a consensus about prevention in the postpartum period in women with thrombophilia. In contrast, prophylaxis in the antepartum period is often determined on an individual basis. We give some indications of the appropriate prophylaxis on the basis of the ACCP recommendations and personal experience.

Life-threatening bleeding in four patients with an unusual excessive response to dabigatran: Implications for emergency surgery and resuscitation

We report two patients with severe thrombocytopenia and life-threatening bleeding that were successfully managed with recombinant activated factor VII (rFVIIa). The first was a 75-year-old male with Waldenström's macroglobulinemia. During a therapeutic course with fludarabine, he developed severe autoimmune thrombocytopenia resistant to conventional treatment, followed by persistent uncontrollable nasal bleeding. Platelet transfusions failed to increase the platelet count and control the hemorrhage. When hemoglobin levels fell below 8.5 g/dL and the patient's clinical condition got much worse, a single dose of 4.8 mg rFVIIa (90 microg/kg) was given as an i.v. bolus. Ten minutes after the rFVIIa injection, nasal bleeding stopped, the patient's clinical condition progressively improved, and splenectomy could be carried out uneventfully 2 days later. The second patient, a 52-year-old female, was under treatment for pre-B lymphoblastic leukemia. She developed severe thrombocytopenia, secondary to chemotherapy, complicated by massive gastrointestinal bleeding. Despite intensive treatment with platelet transfusions, hemorrhage continued and her condition deteriorated rapidly. She was then given an i.v. bolus injection of 4.8 mg rFVIIa, which resulted in cessation of hemorrhage and dramatic improvement of her clinical status. No adverse effects from the treatment with rFVIIa were observed. In conclusion, rFVIIa appears to be an attractive alternative for controlling hemorrhage in patients with severe thrombocytopenia, especially when platelet transfusions are unavailable or ineffective.

New anticoagulants have been designed using advances in the biotechnology and the biochemistry of the clotting factors. They are classified according to their target or their mechanism of action (AT-dependent or AT-independent). Antithrombotic activity after oral administration is another important property. This abstract is restricted to the synthetic pentasaccharide and the ximelagatran/melagatran. Fondaparinux (Arixtra) is a chemically synthesized methoxy derivative of the natural pentasaccharide (MW=1728 Da). Fondaparinux has nearly complete bioavailabity after subcutaneous injection. The elimination half-life is about 17 hours. Fondaparinux is cleared from the kidneys. In contrast to heparin, fondaparinux does not interact with plasma proteins other than antithrombin and it does not cross-react in vitro with heparin induced thrombocytopenia antibodies. Fondaparinux inhibits specifically FXa, although some other targets are suspected (FIXa and FVIIa). Endogenous levels of AT are the rate limiting factor for its anti-Xa activity. Fondaparinux, in contrast to direct FXa inhibitors (i.e. DX-9065a) inhibits free FXa but not the FXa bound to prothrombinase, and it does not prolong PT and aPTT. Fondaparinux inhibits thrombin generation in human plasma. We have shown that the inhibition of thrombin generation by fondaparinux is inversely correlated with thromboplastin concentration. This original observation may explain the absence of any effect of fondaparinux on PT. Melagatran dipeptide (MW=430 Da) is a specific, reversible direct thrombin inhibitor. It inhibits free and clot bound thrombin. Its half-life is 1.7-2.5 hours after i.v. or s.c. administration. Ximelagatran (Exantas), is a pro-drug with a hydroxyamidino instead of amidino-group and an esterified carboxyl-group. It is the first clinically used direct orally acting thrombin inhibitor. Ximelagatran after intestinal absorption is metabolized to melagatran. Melagatran is not metabolized and is cleared through the kidney. Among the specific FXa inhibitors the synthetic pentasaccharide (Fondaparinux-Arixtra) has been approved by FDA and several European health organizations for the prophylaxis of VTE in major orthopedic surgery. No specific antidote has been described for the new antithrombotics. Encouraging results have been obtained from our group on the possible use of rFVIIa (Novoseven). The general opinion is that there is no need for laboratory monitoring of the new antithrombotic agents. Conclusion. The research for safer and more effective anticoagulants has been successful by targeting specific steps in coagulation. These single-targeted agents are challenging multi-targeted drugs (heparins and vitamin-K antagonists). Other drugs including orally active FXa direct inhibitors will probably enrich the armentarium of antithrombotic drugs.

Resume Le premier plan occupe par les heparines de bas poids moleculaire dans la strategie therapeutique des accidents thromboemboliques veineux est une innovation de la derniere reunion de consensus nord-americaine sur les traitements antithrombotiques publiee dans un numero special de la revue Chest en 2001. Compte tenu du rapport benefice-risque particulierement avantageux, cette recommandation est du niveau de preuve le plus eleve soit 1A. Le debut precoce du traitement anticoagulant oral associe a l'utilisation de nomogramme permet de reduire notablement la duree du chevauchement et d'atteindre le seuil d'international normalized ratio (INR) souhaite plus regulierement. La surveillance biologique est simplifee. L'evaluation bi-hebdomadaire de la numeration plaquettaire est systematique durant le pemier mois de traitement alors que l'activite anti-Xa n'est reservee qu'aux patients ayant une fonction renale alteree ou des poids extremes. Cependant, plusieurs points restent encore discutes : l'administration uni ou biquotidienne et la duree du traitement en fonction de la persistance eventuelle de facteurs favorisants, du type de thrombophilie et du terrain. La strategie antithrombotique devient ainsi de plus en plus ciblee, basee sur les preuves et adaptee au cas par cas selon le niveau de risque thrombotique.

New oral factor Xa inhibitors are intended to progressively substitute the oral vitamin K antagonists and parenteral indirect inhibitors of factor Xa in the prevention and treatment of venous and arterial thromboembolic episodes. This article focuses on the main clinical studies and on biological measurements of new oral factor Xa inhibitors, and addresses several safety issues. These newer agents do not require any routine laboratory monitoring of blood coagulation; however, biological tests have been developed in order to assess the plasma concentration of these drugs in several clinical settings. This article reviews these 4 oral direct factor Xa inhibitors.

IntroductionEdoxaban is an oral, once-daily direct factor Xa (FXa) inhibitor. Although rapidly cleared, strategies to reverse edoxaban-mediated effects on anticoagulation are needed in cases of excessive bleeding or emergency. This study evaluated the effect of two prohemostatic agents, recombinant factor VIIa (rFVIIa) and factor VIII inhibitor bypass activity (FEIBA), on the anticoagulatory effects of supratherapeutic concentrations of edoxaban in human whole blood ex vivo.Materials and MethodsBlood samples were collected from six healthy volunteers. Edoxaban (500 or 1000ng/mL), alone or followed by rFVIIa (0.8 or 1.8μg/mL) or FEIBA (0.75 or 1.5 U/mL), was added to an aliquot of each sample. Biomarkers, including prothrombin time (PT), activated partial thromboplastin time (aPTT), extrinsic FXa activity (anti-FXa), intrinsic factor X activity, and D-dimer, were assessed at 0.25, 0.5, 1, 2, and 4hours after adding rFVIIa or FEIBA.ResultsDecreases in measures of PT (p

A variety of pharmaceutical preparations of low-molecular-weight heparins (LMWHs) are available. They belong to the same family of compounds-ie, heparin derivatives with a narrow distribution of mean molecular weights (MWs). LMWHs have different methods of preparation, which result in variations in mean MW, distribution of MW, and pharmacokinetic (PK) and pharmacodynamic (PD) profiles. The mean MW of these compounds ranges from 3,600 to 6,500 daltons. The ratio of anti-Xa (aXa) and anti-IIa (aIIa) activities of the different LMWHs ranges from 1.5 to >10. After subcutaneous (SC) injection of a prophylactic or therapeutic dose, the peak values for plasma aXa or aIIa activity may vary twofold to threefold because of differences in bioavailability, plasma clearance (Clplasma), and half-life (t1/2). The injection of equivalent amounts of product, based on aXa and aIIa international units (IU), may result in different areas under the curve for the respective activities. Although tinzaparin has a high aIIa specific activity per milligram (and consequently, a low aXa/aIIa ratio), SC injection of 40 mg of enoxaparin (4,000 aXa IU) results in a higher aXa peak value in patients with total hip replacement than 4,500 aXa IU of tinzaparin. Differences in aIIa and aXa peak activities are more striking when high doses of LMWHs are used. The activated partial thromboplastin time (aPTT) can be significantly prolonged, an effect that is related to aIIa and aXa activity. The volume of distribution of LMWHs is of the same order of magnitude as that of the plasma volume. The mean retention time of aXa activity varies from 5.2 (dalteparin) to approximately 7 h (enoxaparin, nadroparin). Bioavailability of prophylactic doses of LMWHs ranges from 86% (dalteparin) to 98% (enoxaparin, nadroparin). PK parameters appear to be minimally affected by a patient's age. The Clplasma is different for each LMWH: 16 mL/min enoxaparin, 21 mL/min nadroparin, 33 mL/min dalteparin, 19 mL/min reviparin, and 22 mL/min tinzaparin. Accumulation of product has been observed for almost all LMWHs in patients with renal insufficiency. LMWHs are effective and safe for treatment or prophylaxis of venous thromboembolism during pregnancy, because they do not cross the placenta. No data are available regarding the passage of LMWHs into the milk in lactating women. Although LMWHs are also effective in prevention and treatment of thromboembolic disease in children, optimal use of these agents in pediatric patients has not been determined. In summary, the PD and PK of LMWHs have been well documented and have demonstrated that LMWHs have a more predictable response, a greater bioavailability, and a longer aXa t1/2 than unfractionated heparin. However, their distribution of MW affects their physicochemical and biological properties, as well as PK characteristics. The concept of aXa/aIIa ratio (determined in vitro) does not account for the differing PK of aXa and aIIIa activity in circulating blood.

Background The efficacy and safety of thromboprophylaxis in patients with acute medical illnesses who may be at risk for venous thromboembolism have not been determined in adequately designed trials. Methods In a double-blind study, we randomly assigned 1102 hospitalized patients older than 40 years to receive 40 mg of enoxaparin, 20 mg of enoxaparin, or placebo subcutaneously once daily for 6 to 14 days. Most patients were not in an intensive care unit. The primary outcome was venous thromboembolism between days 1 and 14, defined as deep-vein thrombosis detected by bilateral venography (or duplex ultrasonography) between days 6 and 14 (or earlier if clinically indicated) or documented pulmonary embolism. The duration of follow-up was three months. Results The primary outcome could be assessed in 866 patients. The incidence of venous thromboembolism was significantly lower in the group that received 40 mg of enoxaparin (5.5 percent [16 of 291 patients]) than in the group that received placebo (14.9 percen...

Studies in experimental animal models and in patients receiving low molecular weight heparin (LMWH) to prevent thromboembolic events after surgery have not demonstrated a clear relationship between anti-Xa and anti-IIa activities in plasma and either bleeding or prevention of thrombosis. The relationship between these clinical outcomes and ex vivo anti-Xa and anti-IIa activities, activated partial thromboplastin time (APTT) and D-dimers were evaluated in 440 patients undergoing total hip replacement and given prophylaxis once daily with a LMWH (tinzaparin or enoxaparin) in a multicentre double-blind randomized study. 221 patients received 4500 anti-Xa IU of tinzaparin; 219 patients received 40 mg (4000 anti-Xa IU) of enoxaparin. Both regimens were administered subcutaneously once daily. Blood samples for anti-IIa, anti-Xa, D-dimers levels and APTT were taken at baseline, on day 1, day 5 and on the day of discharge (days 8-14) and clinical assessments were performed dafly until day 14. All patients had bilateral venography between days 8 and 14. All coagulation tests were performed in central laboratories. A significant correlation was observed between anti-IIa activity and anti-Xa activity and the dose of each LMWH injected. The anti-Xa activity was significantly higher with enoxaparin and the anti-IIa activity was significantly higher with tinzaparin. No clear relationship between these two activities and the clinical outcomes was observed. This was also true with regards to APTT. Before and after surgery, D-dimers were significantly higher in patients with deep vein thrombosis (DVT) than in those without DVT but had no predictive value. Interestingly, a significant post-operative increase of D-dimers persisted in both groups of patients during the whole observation period, possibly suggesting that a longer duration of prophylactic treatment may be appropriate.

SummaryConsecutive patients undergoing total hip replacement in 43 centres were randomly assigned to receive blindly either enoxaparin (40 mg) or tinzaparin (4,500 anti-Factor IU Xa), as once daily subcutaneous injections. The first injection was administered 12 h preoperatively. Efficacy was assessed by bilateral venography performed 12-14 days postoperatively. Efficacy and safety were blindly and centrally adjudicated. Among the 499 patients included, 440 had a venogram. The total incidence of DVTs was 44 (20.1%) of the 219 patients of the enoxaparin group and 48 (21.7%) of the 221 patients of the tinzaparin group. The upper limit of the 80% confidence interval of the difference between the two treatment groups was less than 5.0%. Therefore according to the protocol’s specifications equivalence was shown. Proximal DVTs occurred in 10.5% of the enoxaparin group (23 patients) and in 9.5% (21 patients) of the tinzaparin group. No overt major bleeding was observed. One patient in the enoxaparin group developed severe thrombocytopenia and died. The LMWH tinzaparin appears clinically to be as effective and safe as enoxaparin in the prophylaxis of deep vein thrombosis after total hip replacement, at the doses used and under the conditions of this study.