Prevention of major venous thromboembolism following total hip or knee replacement: a randomized comparison of low-molecular-weight heparin with unfractionated heparin (ECHOS Trial)

AIM

Venous thromboembolism remains a frequent complication after total hip or knee replacement surgery despite routine prophylaxis. However, the ability of pharmacologic thromboprophylaxis to prevent major venous thromboembolism, defined as proximal deep vein thrombosis, and/or pulmonary embolism, and/or death, has not been previously validated.

METHODS

In a double-blind randomized study, 2018 patients, undergoing either total hip or knee replacement surgery, were allocated to receive subcutaneous preoperative reviparin (4,200 anti Xa IU) once daily or 7,500 IU unfractionated heparin twice daily, for a minimum of 11 days. The primary efficacy outcome was major venous thromboembolism, defined as the composite of venographically confirmed proximal deep vein thrombosis, and/or symptomatic pulmonary embolism and death, recorded up to day 14.

RESULTS

The primary efficacy outcome was assessed in 1,628 patients and demonstrated a significant reduction in the reviparin group (3.4% [28 of 813 patients] compared with unfractionated heparin (5.5% [45 of 815]) (odds ratio, 0.61; 95% confidence interval, 0.38 to 0.99, P=0.04) by day 11 to 14. A significant reduction in venous thromboembolism was maintained up to 6-8 weeks (3.4% [28 of 813 reviparin patients] versus 5.6% [46 of 815 unfractionated heparin patients]) (odds ratio, 0.6; 95% confidence interval, 0.37 to 0.97, P=0.03). Major bleeding events occurred in 9 reviparin-treated patients (0.9%) and in 12 unfractionated heparin-treated patients (1.2%).

CONCLUSIONS

Prophylaxis with reviparin significantly reduces the risk of major venous thromboembolism compared with unfractionated heparin in patients undergoing elective hip or knee replacement without increasing the risk of bleeding.

Increased levels of inflammatory mediators in lung cancer and their modulation by oral anticoagulant treatment

17050

Background: Venous thromboembolic events (VTE) are associated with lung cancer and significantly contributes to the increased mortality in these patients. While the increased prevalence of VTE is fully recognized in lung cancer, its pathogenesis is not fully understood. Even the patients undergoing therapeutic interventions are at high risk to develop VTE. These patients provide a unique clinical setting to investigate the pathogenesis of lung cancer associated thrombosis. Methods: In a prospective, randomized, controlled study patients with inoperable lung cancer (n = 100) were randomized to receive chemotherapy, radiation and warfarin (INR 1.5–2.5) or chemotherapy, radiation without warfarin (n = 50). Blood samples were drawn prior to and after the second treatment cycle with warfarin. All samples were analyzed for tumor necrosis factor alpha (TNF α), CD 40 ligand (CD 40L), C-reactive protein (CRP), interleukin 1 beta (IL-1β), asymmetric dimethylarginine (ADMA) and nitric oxide (NO). Results: Summarized in the table given below. All of the surrogate markers of inflammation showed a decreased trend (13–50%) in the warfarin treated group, whereas the non-warfarin treated group exhibited an increase (18–46%) in all markers except CRP and ADMA. Conclusions: The levels of various inflammatory markers are upregulated in lung cancer suggesting a pathogenic role of this process in lung cancer. Warfarin down regulated the inflammatory process in contrast to the non-warfarin treated group. The clinical relevance of these observations require additional analysis.

[Table: see text]

No significant financial relationships to disclose.

Nitric oxide and asymmetric dimethylarginine (ADMA) in malignancy associated thrombosis and their modulation by anticoagulants

10573

Background: Cancer associated thrombotic complications are primarily due to endothelial dysfunction and upregulation of inflammatory processes. Nitric oxide (NO) represents one of the major endothelial derived vasoactive mediators. Asymmetric dimethylarginine (ADMA) is an endogenous competitive inhibitor of NO synthase which inhibits NO production at pathophysiologic levels. Plasma ADMA levels are upregulated in atherosclerosis, hypertension, end stage renal disease, chronic heart failure and microangiopathy. Methods: To test the hypothesis that endothelial dysfunction in cancer patients may result in increased ADMA levels, plasma samples were retrospectively analyzed from an open label, multidose, active comparator designed study in which all patients (n = 110) were initially treated with low molecular weight heparin, enoxaparin (E) at 1–1.5 mg/kg sc for 5 days and further subdivided into group E which continued to receive E and warfarin (W) group which was given oral anticoagulants for a period of up to 12 weeks. Baseline blood samples (BL), 5 days post E (IPE) and 4–6 week samples from the E and W were analyzed for ADMA and NO levels by ELISA methods. Results: Both the ADMA and NO levels were markedly elevated in cancer patients. The E treated group showed a marked decrease in the ADMA levels which persisted throughout the treatment period. However, in the W converted group the ADMA levels rebounded to an increased level indicating that E differentially regulated ADMA in these patients. The down regulation pattern of NO was similar for both E and W. Conclusions: These results suggest that patients with cancer and thrombosis exhibit simultaneous upregulation of ADMA and NO. While E and W show a differential regulation of ADMA both result in downregulation of NO. The fact that E regulates ADMA is highly suggestive of its role in iNOS regulation which may be involved in the inflammatory response in cancer patients.

[Table: see text]

No significant financial relationships to disclose.

Comparative tissue factor pathway inhibitor release potential of heparins

Tissue factor pathway inhibitor (TFPI) is released following the administration of unfractionated heparin, low-molecular-weight heparins, defibrotide and PI-88. In this study, the comparative effects of heparin, a low-molecular-weight heparin-gammaparin and a heparin-derived oligosaccharide mixture-subeparin (C3) were studied on functional and immunologic tissue factor pathway inhibitor activity levels in a non-human primate (Macaca mulatta) model. The dose-dependent effect was studied following intravenous and subcutaneous administration. Following the administration of 1 mg/kg of heparin, gammaparin, and C3, the functional levels of TFPI at 5 minutes were 2.40, 2.56, and 1.08 U/mL and the corresponding TFPI immunologic levels were 4.3-, 4.0-, and 2.1-fold, increased, respectively, over the baseline value. From these results, it can be concluded that heparin and gammaparin produced similar levels of TFPI release. Hence, gammaparin and heparin have similar TFPI release potential despite their differences in molecular weight. The influence of molecular weight, charge density, and interactions with heparin cofactor II on TFPI release are also discussed.

Tissue factor pathway inhibitor and thrombin activatable fibrinolytic inhibitor plasma levels following burn and septic injuries in rats

Burn and septic injuries induce profound changes in coagulation status. This study examined the changes in plasma tissue factor pathway inhibitor (TFPI) and thrombin activatable fibrinolytic inhibitor (TAFI) levels in a rat model of burn and septic injuries. Rats underwent 30% TBSA cutaneous scald burn injury and septic insult was induced by caecal ligation and puncture (CLP). CLP was superimposed on burn injury to mimic the clinical model of sepsis complicating burn injury. Rats were pretreated with Cprofloxacin orally to colonize their gut with Enterococcus faecalis. TFPI and TAFI plasma levels were measured using functional activity assay kit with a chromogenic method at 24 and 72 hours following the injuries. TFPI levels decreased significantly at 24 hours in burn, CLP, and burn+CLP groups, followed by incomplete rebound recovery at 72 hours in all three groups. On the other hand, TAFI levels increased significantly at 24- and 72-hour time points in all three groups. These results suggest that burn, septic, and their combined injuries perturb coagulation cascade and thrombotic process toward the procoagulant pathway by impairing fibrinolysis.

Emerging anticoagulant and thrombolytic drugs

Since its discovery, heparin has been used intensely as an anticoagulant for several medical and surgical indications. However, efforts are in progress to replace heparin because of its serious complications, such as intraoperative and postoperative bleeding, osteoporosis, alopecia, heparin resistance, heparin rebound, heparin-induced thrombocytopenia (HIT) and thrombosis syndrome (HITTS), and other disadvantages. Significant developments in the field of new anticoagulants have resulted in the evaluation and introduction of low molecular weight heparins (LMWHs) and heparinoids, hirudin, ancrod, synthetic peptides and peptidomimetics. However, despite significant progress in the development of these new anticoagulants, a better or an ideal anticoagulant for cardiovascular patients is not yet available and heparin still continues to amaze both basic scientists and the clinicians. To minimise the adverse effects of heparin, newer approaches to optimise its use in combination with the new anticoagulants may provide better clinical outcome. In our experience, the off-label use of argatroban at a dose of 300 microg/kg iv. bolus followed by 10 microg/kg/minute infusion in combination with aggrastat (a glycoprotein [GP] IIb/IIIa inhibitor) at a dose of 10 microg/kg iv. bolus followed by an infusion of 0.15 microg/kg/minute in patients with HIT undergoing percutaneous coronary interventions resulted in elevation of celite activated clotting time (ACT) to 300 seconds followed by a gradual decline and the ACT remained above 200 seconds even after 200 min of drug administration. A bewildering array of newer anticoagulants now exist, such as LMWHs and heparinoids, indirect or direct thrombin inhibitors, oral thrombin inhibitors, such as melagatran (AstraZeneca) and HC-977 (Mitsubishi Pharmaceuticals), Factor IXa inhibitors, indirect or direct Factor Xa inhibitors, Factor VIIa/tissue factor (TF) pathway inhibitor, newer antiplatelet agents, such as GPIIb/IIIa inhibitors, fibrin specific thrombolytic agent, such as tenecteplase and modulation of the endogenous fibrinolytic activity by thrombin activatable fibrinolytic inhibitor (TAFI), Factor XIIIa inhibitors and PAI-1 inhibitors. The quest for newer anticoagulant, antiplatelet and fibrinolytic agents will continue until ideal agents are found.

Pharmacologic profile of certoparin

The low molecular weight heparins (LMWHs) are now not only used for the prophylaxis and treatment of deep vein thrombosis (DVT), but also for the management of acute coronary syndromes. Beside these approved usages, the LMWHs have been developed for indications such as thrombotic and ischaemic stroke, cancer-associated thrombotic and vascular disorders, Alzheimer's disease and a variety of inflammatory disorders. In the United States, there are three approved LMWHs (enoxaparin, dalteparin and ardeparin). In Canada, reviparin and tinzaparin are also approved. The European Union has taken the lead; eight LMWHs are approved for various indications. Certoparin represents one of the earlier LMWHs used for DVT prophylaxis and treatment, with additional indications currently under development. Certoparin represents an isoamyl nitrite depolymerised LMWH with comparable structural characteristics to other nitrous acid depolymerised products such as nadroparin and reviparin. While comparable in structure to dalteparin, this agent differs in function due to a secondary purification process that is employed in the manufacture of dalteparin. The preclinical pharmacology of this drug has been extensively investigated. Although indication specific dosing and the optimisation of use in, for example, acute coronary syndromes and thrombotic stroke, may be require, certoparin represents a typical LMWH with comparable performance characteristics to some other agents. This chapter describes some of the preclinical and clinical pharmacologic characteristics of this drug. This information will be useful in designing clinical trials for newer indications of this drug.

Synthetic and recombinant antithrombin drugs

As the final enzyme in the activation of the coagulation system, the serine protease, thrombin, is believed to be an important target for the development of new anticoagulant/antithrombotic drugs. Direct thrombin inhibitors are either derived from natural sources, such as hirudin or are chemically synthesised, such as argatroban. The coupling of hirudin or parts of it with other entities leads to novel agents with different pharmacokinetic and pharmacodynamic characteristics, such as polyethylene glycol (PEG)-hirudin or the hirulogs. Due to the reversible or irreversible inactivation of the enzyme, thrombin inhibitors exert strong anticoagulant effects that can be measured in global clotting assays. Furthermore, these compounds inhibit thrombin-induced platelet reactions and influence other cellular, receptor-mediated actions of thrombin, e.g., on vascular cells. Directly acting thrombin inhibitors prevent blood clotting and are also capable of inhibiting clot-associated thrombin; however, they do not effectively block the further generation of the enzyme. Comprehensive experimental studies suggest that thrombin inhibitors may be effective drugs in a wide range of intravascular thrombus formation, also including the inhibition of vascular restenosis. Recent clinical trials revealed the effectiveness of direct thrombin inhibitors in various thrombotic and cardiovascular indications, but also a tendency to an increased risk of bleeding complications. At present, thrombin inhibitors are the most promising class of drugs for the initial therapy of patients with heparin-induced thrombocytopaenia (HIT) or the heparin-induced thrombocytopaenia and thrombosis syndrome (HITTS). They are also useful for the management of venous thrombosis and for acute ischaemic syndromes as well as for invasive procedures. However, with regard to the long-term outcome, a superiority of thrombin inhibitors over heparin has not yet been demonstrated. Several important issues, such as monitoring, pharmacological antagonism and drug interactions will also play an important role in the development of these new drugs. Further clinical trials are required to confirm the effectiveness of direct thrombin inhibitors in the prophylaxis and treatment of various thromboembolic and cardiovascular disorders.