The direct thrombin inhibitor melagatran followed by oral ximelagatran compared with enoxaparin for the prevention of venous thromboembolism after total hip or knee replacement: the EXPRESS study

Emergence of new oral antithrombotics: a critical appraisal of their clinical potential

In Western countries, venous thromboembolism (VTE) is a widespread and serious disorder, with hospital admission rates that appear to be increasing. Current anticoagulant therapies available for the prevention and treatment of VTE have several drawbacks that make them either difficult to manage effectively, due to a need for careful monitoring to control coagulation, or, in the case of parenterally administered agents, inconvenient for long-term use. To address some of these issues, new anticoagulants are in clinical development that can be orally administered and directly target specific factors in the coagulation cascade. This article reviews the rationale behind development of these novel agents and provides a critical appraisal of their clinical potential. In addition, the impact that the introduction of such agents into clinical practice would have is discussed from the patient perspective.

Lower limb contrast venography: a modified technique for use in thromboprophylaxis clinical trials for the accurate evaluation of deep vein thrombosis

Lower limb venography remains the imaging modality of choice for detection of asymptomatic deep vein thrombosis (DVT) in clinical trials of anticoagulant agents. A variety of techniques of venography have been described. Here, we describe a modified technique (the "King's" technique) developed to increase the overall adequacy of identification of lower limb veins and detection of small asymptomatic DVT. Essential elements include proper preparation of patients prior to their arrival in the radiology department, intermittent use of tourniquets to ensure complete and adequate deep vein filling, use of a consistent image acquisition sequence and visualization of all veins in at least two different planes. Use of this technique minimizes technical difficulties, provides improved patient through-put in "busy" fluoroscopy units and, ultimately, improves "off-site" levels of adjudication.

Ximelagatran/melagatran against conventional anticoagulation: A meta-analysis based on 22,639 patients

BACKGROUND

The oral direct thrombin inhibitor ximelagatran, and its active form, melagatran, have been tested in various clinical conditions as a promising alternative to conventional anticoagulant therapy (CAT), despite some concerns over potentially serious liver injury.

OBJECTIVES

To assess its risk/benefit profile, a systematic review and meta-analysis of all randomised controlled trials (RCTs) comparing xi-/melagatran to CAT was performed.

METHODS

Leading medical databases were searched. The rates of major adverse events (MAE: all cause death, nonfatal myocardial infarction, nonfatal thromboembolic stroke, nonfatal pulmonary embolism), major bleeds (MB), and hepatotoxicity were compared. Out of 140 potentially relevant citations, 13 RCTs enrolling 22,639 patients were included. Indications for treatment were: 1) perioperative prophylaxis of deep vein thrombosis (DVT); 2) management of DVT; and 3) stroke prevention in atrial fibrillation.

RESULTS

Overall, the risk of MAE (OR 0.98 [0.83-1.17]) and MB (OR 1.01 [0.69-1.47]) did not differ significantly between xi-/melagatran and CAT. There was a clear trend towards an increased risk of hepatotoxicity (OR 1.74 [0.50-6.01]), with an incidence of 5.8% with xi-/melagatran versus 2.3% with CAT (p<0.001); more specifically, the rate of hepatotoxicity was markedly augmented in the management of DVT (OR 5.16 [3.38-7.89]), for treatment durations > or = 3 months (OR 6.73 [5.01-9.05]), and in the prevention of atrial fibrillation-related stroke (OR 8.31 [5.65-12.23]). Two fatal cases of liver injury occurred with xi-/melagatran.

CONCLUSIONS

Although comparable to CAT in terms of MAE and MB, xi-/melagatran carries a prohibitive risk of hepatotoxicity that cannot be ignored. Newer long-term alternatives are urgently needed.

Oral dabigatran etexilate vs. subcutaneous enoxaparin for the prevention of venous thromboembolism after total knee replacement: the RE-MODEL randomized trial

BACKGROUND

Oral anticoagulants, such as dabigatran etexilate, an oral, direct thrombin inhibitor, that do not require monitoring or dose adjustment offer potential for prophylaxis against venous thromboembolism (VTE) after total knee replacement surgery.

METHODS

In this randomized, double-blind study, 2076 patients undergoing total knee replacement received dabigatran etexilate, 150 mg or 220 mg once-daily, starting with a half-dose 1-4 hours after surgery, or subcutaneous enoxaparin 40 mg once-daily, starting the evening before surgery, for 6-10 days. Patients were followed-up for 3 months. The primary efficacy outcome was a composite of total VTE (venographic or symptomatic) and mortality during treatment, and the primary safety outcome was the incidence of bleeding events.

RESULTS

The primary efficacy outcome occurred in 37.7% (193 of 512) of the enoxaparin group versus 36.4% (183 of 503) of the dabigatran etexilate 220 mg group (absolute difference, -1.3%; 95% CI, -7.3 to 4.6) and 40.5% (213 of 526) of the 150 mg group (2.8%; 95% CI, -3.1 to 8.7). Both doses were noninferior to enoxaparin based on the pre-specified noninferiority criterion. The incidence of major bleeding did not differ significantly between the three groups (1.3% versus 1.5% and 1.3% respectively). No significant differences in the incidences of liver enzyme elevation and acute coronary events were observed during treatment or follow-up.

CONCLUSIONS

Dabigatran etexilate (220 mg or 150 mg) was at least as effective and with a similar safety profile as enoxaparin for prevention of VTE after total knee-replacement surgery.

Dabigatran etexilate versus enoxaparin for prevention of venous thromboembolism after total hip replacement: a randomised, double-blind, non-inferiority trial

BACKGROUND

After hip replacement surgery, prophylaxis following discharge from hospital is recommended to reduce the risk of venous thromboembolism. Our aim was to assess the oral, direct thrombin inhibitor dabigatran etexilate for such prophylaxis.

METHODS

In this double-blind study, we randomised 3494 patients undergoing total hip replacement to treatment for 28-35 days with dabigatran etexilate 220 mg (n=1157) or 150 mg (1174) once daily, starting with a half-dose 1-4 h after surgery, or subcutaneous enoxaparin 40 mg once daily (1162), starting the evening before surgery. The primary efficacy outcome was the composite of total venous thromboembolism (venographic or symptomatic) and death from all causes during treatment. On the basis of the absolute difference in rates of venous thromboembolism with enoxaparin versus placebo, the non-inferiority margin for the difference in rates of thromboembolism was defined as 7.7%. Efficacy analyses were done by modified intention to treat. This trial is registered with ClinicalTrials.gov, number NCT00168818.

FINDINGS

Median treatment duration was 33 days. 880 patients in the dabigatran etexilate 220 mg group, 874 in the dabigatran etexilate 150 mg group, and 897 in the enoxaparin group were available for the primary efficacy outcome analysis; the main reasons for exclusion in all three groups were the lack of adequate venographic data. The primary efficacy outcome occurred in 60 (6.7%) of 897 individuals in the enoxaparin group versus 53 (6.0%) of 880 patients in the dabigatran etexilate 220 mg group (absolute difference -0.7%, 95% CI -2.9 to 1.6%) and 75 (8.6%) of 874 people in the 150 mg group (1.9%, -0.6 to 4.4%). Both doses were thus non-inferior to enoxaparin. There was no significant difference in major bleeding rates with either dose of dabigatran etexilate compared with enoxaparin (p=0.44 for 220 mg, p=0.60 for 150 mg). The frequency of increases in liver enzyme concentrations and of acute coronary events during the study did not differ significantly between the groups.

INTERPRETATION

Oral dabigatran etexilate was as effective as enoxaparin in reducing the risk of venous thromboembolism after total hip replacement surgery, with a similar safety profile.

The direct thrombin inhibitor ximelagatran/melagatran: a systematic review on clinical applications and an evidence based assessment of risk benefit profile

The direct thrombin inhibitor, ximelagatran, and its active form, melagatran (X/M), have been compared against conventional anticoagulant therapy (CAT) in many clinical settings. Their risk-benefit profile drove large debate until withdrawal by the manufacturer. A systematic review of all published randomized trials has been performed and a meta-analysis of randomised controlled trial (RCT) of X/M versus CAT. Major medical databases were searched for RCTs. Major adverse events (MAE: all cause death, nonfatal myocardial infarction, nonfatal thromboembolic stroke, pulmonary embolism), major bleeds (MB), minor bleeds and the rate of hepatotoxicity (HT) were compared. In terms of efficacy, X/M was at least as effective as, or even superior to, CAT. In terms of safety, the overall risk of MAE, MB, minor bleeds and HT was not significantly different for X/M compared with CAT. According to individual clinical settings, X/M was associated with a lower risk of MB but a prohibitive higher risk of HT in those clinical settings requiring prolonged treatment.

Association between asymptomatic deep vein thrombosis detected by venography and symptomatic venous thromboembolism in patients undergoing elective hip or knee surgery

BACKGROUND

Venography is commonly used to compare the efficacy of different thromboprophylaxis strategies for preventing deep vein thrombosis (DVT) in patients undergoing total hip replacement (THR) or total knee replacement (TKR).

METHODS

We explored the relation between asymptomatic DVT and symptomatic venous thromboembolism (VTE) in patients undergoing THR or TKR treated with standard doses of enoxaparin (30 mg b.i.d. or 40 mg o.d.) by comparing the incidence of asymptomatic DVT in venographic studies with the incidence of symptomatic VTE in studies where venography was not performed.

RESULTS

In 10 venographic studies involving 5796 patients, the incidence of asymptomatic DVT after THR was 13.2% [95% CI, 12.2-14.2%] and after TKR was 38.1% (95% CI, 35.5-40.8%). In two studies involving 3500 patients who did not undergo venography, the 90-day incidence of symptomatic VTE after THR was 2.7% (95% CI, 2.1-3.4%) and after TKR was 1.8% (95% CI, 0.9-2.7%). For every symptomatic VTE in THR studies where venography was not performed there were five asymptomatic DVTs in the venographic studies; for TKR, the ratio was 1:21. The incidence of asymptomatic DVT and the symptomatic VTE/asymptomatic DVT ratio was influenced by the venogram reading committee (Gothenburg vs. Hamilton: total DVT after THR, 19.5% vs. 8.7%, P < 0.0001; for TKR, 42.7% vs. 27.2%, P < 0.0001).

CONCLUSIONS

Comparisons across trials show a consistent relation between asymptomatic venographic DVT in patients undergoing elective THR or TKR surgery and symptomatic VTE in patients not undergoing venography. Differences exist in the strength of the relation depending on the type of surgery and the venogram reading committee.

Determination of ximelagatran, melagatran and two intermediary metabolites in plasma by mixed-mode solid phase extraction and LC–MS/MS

An analytical method was developed for the determination of ximelagatran, an oral direct thrombin inhibitor, its active metabolite melagatran, and the two intermediate metabolites, OH-melagatran and ethyl-melagatran in human plasma. Extraction of plasma was carried out on a mixed mode bonded sorbent material (C8/SO(3)(-)). All four analytes, including their isotope-labelled internal standards, were eluted at high ionic strength with a mixture of 50% methanol and 50% buffer (0.25 M ammonium acetate and 0.05 M formic acid, pH 5.3) with an extraction recovery above 80%. The extracts were demonstrated to be clean in terms of a low concentration of albumin and lysoPC. The sample extraction was fully automated and performed in 96-well plates using a Tecan Genesis pipetting robot. Analysis of the extracts were performed with liquid chromatography followed by positive electrospray ionization mass spectrometry. The low organic content and the low pH of the extracts allowed for, after dilution 1:3 with buffer, direct injection onto the LC-column. The four analytes were separated on a C18 analytical LC-column using gradient elution with the acetonitrile concentration varying from 10 to 30% (v/v) and the ammonium acetate and acetic acid concentration kept constant at 10 and 5 mmol/L, respectively, at a flow rate of 0.75 mL/min. Linearity was achieved over the calibrated range 0.010-4.0 micromol/L with accuracy and relative standard deviation in the range 96.9-101.2% and 6.6-17.1%, respectively at LLOQ, and in the range 94.7-102.6% and 2.7-6.8%, respectively at concentrations above 3 x LLOQ. The method replaces a manual method, and displays the advantages of having a fully automated sample clean-up, no evaporation/reconstitution step, high recovery, and complete LC-separation of all four analytes.

[New antitoagulants]

In contrast to older anticoagulant agents vitamin K antagonists and heparins, the new ones are directed towards a single target in general. The main characteristics of the new agents are: their site of action in the coagulation cascade and their mechanism of action which is indirect, antithrombin dependent, most often such as Fondaparinux and Idraparinux or direct such as Dabigatran, Rivaroxaban; the specificity of the new molecules, since they must not interact with other enzymes: trypsin, kallikrein, t-PA, etc...; their mode of administration parenteral and/or oral; their pharmacokinetics and their clearance frequently by the kidney (Hirudin, fondaparinux) or through hepatic metabolism (argatroban); tolerance including for all compounds the bleeding risk or an unexpected hepatic intolerance for Ximelagatran; the availability of a specific antidote and the cost of the drug; one compound is registered in France Arixtra Fondaparinux in major orthopedic surgery and in the treatment of venous thromboembolism and in prophylactic treatment in medical patients. However, the main indications of interest for these new drugs is atrial fibrillation. There is a real need in this indication and the number of patients to treat is growing with the longer life expectancy.

Pharmacokinetics and pharmacodynamics of the oral direct thrombin inhibitor ximelagatran co-administered with different classes of antibiotics in healthy volunteers

OBJECTIVE

To study the effects of amoxicillin, doxycycline, ciprofloxacin, azithromycin, and cefuroxime on the pharmacokinetics and pharmacodynamics of melagatran, the active form of the oral direct thrombin inhibitor ximelagatran, which is a substrate for the P-glycoprotein pump (P-gp) transporter but is not metabolized by the cytochrome P450 (CYP450) enzyme system.

METHODS

Five parallel groups of 16 healthy volunteers received two sequential treatments. The first treatment was a single 36-mg dose of ximelagatran. During the second treatment period, one of the above antibiotics was given on days 1-5 after a washout of at least 2 days. A single 36-mg oral dose of ximelagatran was given on the mornings of days 1 and 5 of the second treatment period.

RESULTS

No pharmacokinetic interactions were detected between ximelagatran and amoxicillin, doxycycline, or ciprofloxacin as the least-squares geometric mean treatment ratio of ximelagatran with-to-without antibiotic fell within the intervals of 0.80-1.25 for the area under the curve (AUC) and 0.7-1.43 for C(max). After co-administration with azithromycin, the least square mean ratio with-to-without antibiotic for AUC of melagatran was 1.60 (90% CI, 1.40-1.82) on day 1 and 1.41 (90% CI, 1.24-1.61) on day 5. For melagatran C(max), the corresponding ratios were 1.63 (90% CI, 1.38-1.92) and 1.40 (90% CI, 1.18-1.66). After co-administration with cefuroxime, the ratios were 1.23 (90% CI, 1.07-1.42) and 1.16 (90% CI, 0.972-1.38) for AUC and 1.33 (90% CI, 1.07-1.66) and 1.19 (90%CI, 0.888-1.58) for C(max) of melagatran. Co-administration with the antibiotics did not change mean time to C(max), half-life, or renal clearance of melagatran. The melagatran plasma concentration-response relationship for activated partial thromboplastin time (APTT) prolongation was not altered by any of the studied antibiotics, but the increased plasma concentrations of melagatran after co-administration of ximelagatran with azithromycin resulted in a minor increase in the mean maximum APTT of about 15%.

CONCLUSION

The pharmacokinetics of ximelagatran were not affected by amoxicillin, doxycycline, or ciprofloxacin. Melagatran exposure was increased when ximelagatran was co-administered with azithromycin and, to a lesser extent, with cefuroxime. APTT was not significantly altered by any of the antibiotics.

Ximelagatran: direct thrombin inhibitor

Warfarin sodium is an effective oral anticoagulant drug. However, warfarin has a narrow therapeutic window with significant risks of hemorrhage at therapeutic concentrations. Dosing is difficult and requires frequent monitoring. New oral anticoagulant agents are required to improve current anticoagulant therapy. Furthermore, while warfarin is effective in venous disease, it does not provide more than 60% risk reduction compared with placebo in venous thrombosis prophylaxis and considerably lower risk reduction in terms of arterial thrombosis. Ximelagatran is an oral pro-drug of melagatran, a synthetic small peptidomimetic with direct thrombin inhibitory actions and anticoagulant activity. As an oral agent, ximelagatran has a number of desirable properties including a rapid onset of action, fixed dosing, stable absorption, apparent low potential for medication interactions, and no requirement for monitoring of drug levels or dose adjustment. It has a short plasma elimination half-life of about 4 hours in cases of unexpected hemorrhage or need for reversal. Its main toxicity relates to the development of abnormal liver biochemistry and/or liver dysfunction with “long-term” use of the drug. This usually occurs within the first 6 months of commencing therapy, with a small percentage of patients developing jaundice. The biochemical abnormality usually resolves despite continuation of the drug. The cause of this toxicity remains unknown. Clinical studies to date have shown that ximelagatran is noninferior to warfarin in stroke prevention in patients with nonvalvular atrial fibrillation, noninferior to standard therapy as acute and extended therapy of deep vein thrombosis (DVT), and superior to warfarin for the prevention of venous thromboembolism post-major orthopedic surgery. It has also been shown to be more effective than aspirin alone for prevention of recurrent major cardiovascular events in patients with recent myocardial infarction.

New anticoagulants for the prevention and treatment of venous thromboembolism

Anticoagulant therapy is effective at preventing the development of venous thromboembolism in high-risk patients, and reduces morbidity and mortality in individuals with established thromboembolic disease. Vitamin K antagonists and heparins are currently the most commonly used anticoagulant drugs, but they have practical limitations. Therefore, new antithrombotic agents with predictable dose-responses (thereby decreasing the need for monitoring without compromising efficacy or safety), ideally available in an oral formulation and with a rapidly reversible anticoagulant effect, are needed. New drugs fulfilling some of the above criteria have been developed and have proven to be effective agents for the treatment and prevention of venous thromboembolism.

Dose-escalation study of rivaroxaban (BAY 59-7939)--an oral, direct Factor Xa inhibitor--for the prevention of venous thromboembolism in patients undergoing total hip replacement

INTRODUCTION

Rivaroxaban (BAY 59-7939) is a novel, oral, direct Factor Xa inhibitor in clinical development for the prevention of thromboembolic disorders. The aim of this study was to demonstrate proof-of-principle for rivaroxaban.

MATERIALS AND METHODS

This was an open-label, dose-escalation study to assess the efficacy and safety of rivaroxaban, relative to enoxaparin, for the prevention of venous thromboembolism (VTE) after total hip replacement surgery. Patients were randomized in a 3:1 ratio to rivaroxaban (2.5, 5, 10, 20 and 30 mg twice daily [bid] or 30 mg once daily [od] starting 6-8 h after surgery) or enoxaparin (40 mg od starting the evening before surgery). Therapy continued until mandatory bilateral venography was performed 5-9 days after surgery.

RESULTS

A total of 625 patients received therapy, of whom 466 patients were eligible for the per-protocol efficacy analysis. The primary efficacy endpoint - deep vein thrombosis (DVT), pulmonary embolism (PE) or all-cause mortality - occurred in 22.2%, 23.8%, 20.0%, 10.2%, 17.4%, 15.1% and 16.8% of patients receiving rivaroxaban 2.5, 5, 10, 20, 30 mg bid, 30 mg od and enoxaparin, respectively. The dose-response relationship with rivaroxaban for the primary efficacy endpoint was not statistically significant (p=0.0504), although major VTE (proximal DVT, PE and VTE-related death) decreased dose dependently with rivaroxaban (p=0.0108). Major, post-operative bleeding increased dose dependently with rivaroxaban (p=0.0008), occurring in 0-10.8% of patients, compared with 0% in patients receiving enoxaparin.

CONCLUSIONS

This study demonstrated proof-of-principle for rivaroxaban for the prevention of VTE after total hip replacement surgery.

Management of venous thromboembolism in the elderly

In this review the authors discuss the use of oral and parenteral anticoagulants for the prevention and treatment of venous thromboembolism (VTE) in the elderly. The use of anticoagulant agents in VTE prophylaxis and treatment in the elderly is complicated by an increase with age in the presence of multiple risk factors and co-morbidities that may increase the risk of both VTE and bleeding. Age itself is identified as an independent risk factor for thromboembolism. VTE is underdiagnosed in the elderly population, and routine prophylaxis frequently falls short of the levels required according to level of risk. Although appropriate anticoagulation of at-risk patients offers a means of reducing the significant VTE burden in this population, concerns have been raised over the use of anticoagulants in a patient group in whom multiple risk factors are common. Bleeding in the elderly can be exacerbated by reduced renal clearance and hypersensitivity to oral anticoagulants that may lead to over-anticoagulation. Although bleeding due to anticoagulant therapy is a serious issue in the elderly, it is often overemphasized, given the therapeutic value otherwise observed in treating this patient group. Warfarin is still used in VTE prophylaxis after orthopaedic surgery and for long-term VTE treatment. Unfractionated and low-molecular-weight heparins (LMWHs) have been shown to be safe and effective in the prophylaxis of VTE, and are now being shown to be as effective as warfarin in the initial and long-term treatment of VTE. LMWHs confer the advantage over unfractionated heparin of subcutaneous once-daily administration with no requirement for laboratory monitoring of their anticoagulant effect, which allows for the convenience of outpatient therapy. New anticoagulants that may be of potential benefit in this patient population include fondaparinux sodium, but clinical experience of this drug in the elderly remains limited.

New versus established drugs in venous thromboprophylaxis: efficacy and safety considerations related to timing of administration

European surgeons generally administer thromboprophylaxis with low-molecular-weight heparins (LMWHs) at high doses 12 hours preoperatively in response to findings that surgery-related deep-vein thrombosis typically originates at the time of major orthopedic surgery or shortly afterwards. North American surgeons, in contrast, generally administer LMWHs at an almost 50% higher dose than that given in Europe 12-24 hours postoperatively, even though both pre- and postoperative administration are considered suitable in current guidelines. This review therefore examines how close to major orthopedic surgery thromboprophylaxis is administered, and the subsequent effect of timing on clinically relevant efficacy and safety parameters. The trials examined involve fondaparinux sodium (fondaparinux) and (xi)melagatran, in comparison with the established LMWHs enoxaparin sodium (enoxaparin) and dalteparin. In key trials, fondaparinux reduced the risk of asymptomatic and clinical venous thromboembolism (VTE) by 55% compared with enoxaparin, at the expense of a 1.6-fold higher risk of bleeding. While the studies were not designed to compare efficacy endpoints based on clinical outcomes, no significant difference was demonstrated for symptomatic VTE. The fact that the enoxaparin regimen was started at the upper limits of its recommended initiation timeframe may have significantly influenced the results of comparative studies, given that several meta-analyses found that the timing of LMWH initiation significantly influenced its effectiveness on asymptomatic VTE and major bleedings. Compared with once-daily LMWH in European trials, early postoperative doses/regimens of twice-daily (xi)melagatran did not increase severe bleeding and was significantly less effective at preventing asymptomatic total VTE in patients who had undergone total hip-replacement surgery. When used according to the 'knife-to-skin' protocol, the melagatran regimen was superior to enoxaparin in preventing major asymptomatic VTE, but at the cost of a higher rate of major bleeding. In North America, the delayed postoperative administration of (xi)melagatran (oral only) was less effective than the postoperative twice-daily enoxaparin regimen with regard to asymptomatic total and major VTE. Our analysis highlights the fact that differences in efficacy and safety data in clinical trials of thromboprophylaxis might also be linked to differences in the timing of initiation. However, it is not possible to assess the importance of this 'time effect' among other factors considered as drug-specific properties (pharmacokinetics, mode of action, dosage) and evaluate their respective contribution in the observed differences. To avoid unbiased comparison in further studies, the possible effect of timing should be taken into account and, when feasible, both therapies started at the same time. For instance, harmonizing the initiation of thromboprophylaxis 6-8 or 12 hours postoperatively could be two acceptable harmonized options for scheduling in clinical trials.

A once-daily, oral, direct Factor Xa inhibitor, rivaroxaban (BAY 59-7939), for thromboprophylaxis after total hip replacement

BACKGROUND

Rivaroxaban (BAY 59-7939)--an oral, direct Factor Xa inhibitor--could be an alternative to heparins and warfarin for the prevention and treatment of thromboembolic disorders.

METHODS AND RESULTS

This randomized, double-blind, double-dummy, active-comparator-controlled, multinational, dose-ranging study assessed the efficacy and safety of once-daily rivaroxaban relative to enoxaparin for prevention of venous thromboembolism in patients undergoing elective total hip replacement. Patients (n=873) were randomized to once-daily oral rivaroxaban doses of 5, 10, 20, 30, or 40 mg (initiated 6 to 8 hours after surgery) or a once-daily subcutaneous enoxaparin dose of 40 mg (given the evening before and > or = 6 hours after surgery). Study drugs were continued for an additional 5 to 9 days; mandatory bilateral venography was performed the following day. The primary end point (composite of any deep vein thrombosis, objectively confirmed pulmonary embolism, and all-cause mortality) was observed in 14.9%, 10.6%, 8.5%, 13.5%, 6.4%, and 25.2% of patients receiving 5, 10, 20, 30, and 40 mg rivaroxaban, and 40 mg enoxaparin, respectively (n=618, per-protocol population). No significant dose-response relationship was found for efficacy (P=0.0852). Major postoperative bleeding was observed in 2.3%, 0.7%, 4.3%, 4.9%, 5.1%, and 1.9% of patients receiving 5, 10, 20, 30, and 40 mg rivaroxaban, and 40 mg enoxaparin, respectively (n=845, safety population), representing a significant dose-response relationship (P=0.0391).

CONCLUSIONS

Rivaroxaban showed efficacy and safety similar to enoxaparin for thromboprophylaxis after total hip replacement, with the convenience of once-daily oral dosing and without the need for coagulation monitoring. When both efficacy and safety are considered, these results suggest that 10 mg rivaroxaban once daily should be investigated in phase III studies.

Ximelagatran versus warfarin for prophylaxis of venous thromboembolism in major orthopedic surgery: systematic review of randomized controlled trials

BACKGROUND

Ximelagatran has been recently studied for prophylaxis in surgical orthopedic cases.

PURPOSE

We proposed to establish whether interventions involving ximelagatran, as compared with warfarin, would increase thromboembolic prophylaxis in patients undergoing major orthopedic knee surgery.

DATA SOURCE

Studies with random assignment were identified by an electronic search of the medical literature up to 2006. Data were double-entered into the Review Manager software, version 4.2.5.

DATA SYNTHESIS

We included three well-conducted clinical trials involving 4,914 participants. Sub-groups with two dosages of ximelagatran (24 mg and 36 mg, b.i.d.), were defined. Ximelagatran showed significantly lower frequency of total venous thromboembolism (VTE) than warfarin, but only with the 36-mg dosage (risk relative, RR: 0.72; 95% confidence interval, CI: 0.64-0.81; p < 0.00001). For the 24-mg subgroup, total VTE frequency was similar (RR: 0.86; 95% CI: 0.73-1.01; p = 0.06). No significant differences were shown with either ximelagatran dosage for deep vein thrombosis (DVT), pulmonary embolism, any bleeding or severe bleeding. At the end of the treatment, alanine aminotransferase (ALT) elevation was less frequent in the 24-mg ximelagatran sub-group (RR: 0.33; 95% CI: 0.12-0.91; p = 0.03], but during the follow-up period, the ALT elevation rate was greater in the 36-mg ximelagatran group (RR: 6.97; 95% CI: 1.26-38.50; p = 0.03].

CONCLUSIONS

Ximelagatran appears to be more effective than warfarin when used in higher dosages (36 mg b.i.d.), but at the expense of increased frequency of ALT elevation during the follow-up period.

Ximelagatran, the New Oral Anticoagulant: Would Warfarin Survive the Challenge?

The last decade witnessed major advances in the prevention and treatment of venous as well as of arterial thrombosis. Limitations of existing anticoagulants led to the development of novel therapeutic approaches. Ximelagatran is a new direct thrombin inhibitor (DTI) that is given orally, without the need for close monitoring. This compound was tried in the treatment of active venous thromboembolism, and the results were encouraging. Randomized trials suggest that ximelagatran is not inferior to warfarin in the prevention of stroke in patients with nonvalvular atrial fibrillation. Multiple controlled, prospective trials compared ximelagatran with low molecular weight heparin or warfarin in prevention of venous thromboembolism in patients undergoing major orthopedic procedures. The results of these clinical trials are reviewed in this article. Because of certain safety concerns (increased liver enzymes, potential hepatonecrosis, and increased coronary events) ximelagatran has not yet been approved by the FDA. Additional studies may be required to address these concerns. Ximelagatran has been approved, however, by the European regulatory authorities for short-term thromboprophylaxis. The success of ximelagatran or other oral antithrombin agents would provide significant proof of the concept for the long-term use of oral antithrombins in the prevention and treatment of both arterial and venous thrombosis.

Prevention of postoperative venous thromboembolism. Risk assessment and methods of prophylaxis

PURPOSE

To describe risk assessment models that have been developed to stratify patients into different risk levels of postoperative venous thromboembolism (VTE) and then to review the different methods of prophylaxis and to outline the evidence supporting their effectiveness and safety.

SOURCE

Our review of the literature is focused on consensus documents, recent large randomized trials and meta-analyses.

PRINCIPAL FINDINGS

The risk of VTE is determined by the type of surgery and underlying patient factors. Risk assessment models are useful in stratifying patients into different VTE risk levels. However, multiple risk factors are often present in the same patient and in practice the evaluation of their relative contribution to the overall risk remains difficult. A variety of prophylactic strategies including physical and pharmacological methods have been shown to be effective in different patient groups. Patients with a moderate or high risk of VTE should receive prophylaxis consisting of an antithrombotic agent, unless contraindicated, used alone or in combination with a mechanical method. Recommendations concerning which prophylaxis to use and how intensive it should be are based mainly on data from trials using surrogate endpoints, and do not translate easily into practical decisions aiming to reduce the incidence of symptomatic events.

CONCLUSION

Although risk assessment models and recommendations provided by consensus documents are of practical assistance, a decision concerning any patient is best made by combining recommendations of the literature with clinical judgment, including individual patient risk factors for thrombosis and bleeding.

Incorrect use of thromboprophylaxis for venous thromboembolism in medical and surgical patients: results of a multicentric, observational and cross-sectional study in Brazil

OBJECTIVES

Although effective strategies for the prevention of venous thromboembolism (VTE) are widely available, a significant number of patients still develop VTE because appropriate thromboprophylaxis is not correctly prescribed. We conducted this study to estimate the risk profile for VTE and the employment of adequate thromboprophylaxis procedures in patients admitted to hospitals in the state of São Paulo, Brazil.

METHODS

Four hospitals were included in this study. Data on risk factors for VTE and prescription of pharmacological and non-pharmacological thromboprophylaxis were collected from 1454 randomly chosen patients (589 surgical and 865 clinical). Case report forms were filled according to medical and nursing records. Physicians were unaware of the survey. Three risk assessment models were used: American College of Chest Physicians (ACCP) Guidelines, Caprini score, and the International Union of Angiololy Consensus Statement (IUAS). The ACCP score classifies VTE risk in surgical patients and the others classify VTE risk in surgical and clinical patients. Contingency tables were built presenting the joined distribution of the risk score and the prescription of any pharmacological and non-pharmacological thromboprophylaxis (yes or no).

RESULTS

According to the Caprini score, 29% of the patients with the highest risk for VTE were not prescribed any thromboprophylaxis. Considering the patients under moderate, high or highest risk who should be receiving prophylaxis, 37% and 29% were not prescribed thromboprophylaxis according to ACCP (surgical patients) and IUAS risk scores, respectively. In contrast, 27% and 42% of the patients at low risk of VTE, according to Caprini and IUAS scores, respectively, had thromboprophylaxis prescribed.

CONCLUSION

Despite the existence of several guidelines, this study demonstrates that adequate thromboprophylaxis is not correctly prescribed: high-risk patients are under-treated and low-risk patients are over-treated. This condition must be changed to insure that patients receive adequate treatment for the prevention of thromboembolism.

Review of the rebound phenomenon in new anticoagulant treatments

BACKGROUND

The launch of new anticoagulant treatments has sparked debate as to the optimal drug to use for primary prevention of venous thromboembolism (VTE) in major orthopaedic surgery, for the treatment of VTE, and for stroke prevention in atrial fibrillation, taking into account both efficacy and tolerability. Newer drugs such as fondaparinux and ximelagatran have shown improvements in short-term efficacy or convenience, but such effects may be offset by reduced tolerability. They also raise the question of a possible delayed increase in thromboembolic events after these drugs are stopped, the so-called 'rebound effect'.

OBJECTIVE

To review pharmacological and clinical data describing the rebound effect associated with new and standard anticoagulant drugs.

RESEARCH DESIGN AND METHODS

Computerized searches, covering the period 1960-2005 for the historical background and physiopathology review, and from 1999 to 2005 for the clinical trial analysis, were performed on BIOSIS, PubMed and clinicaltrials.gov databases. The terms 'rebound', 'anticoagulant', and 'heparin' were used. Only articles written in English were reviewed. Articles with drug interactions from other therapeutic classes or types of vascular surgery and commentary articles were excluded.

RESULTS

Available data in relation to a possible rebound phenomenon following cessation of active treatment are very limited. Results coming mainly from orthopaedic surgery trials suggest an increased rate of venous or arterial thromboembolic events with newer anticoagulants, compared with standard anticoagulant therapy. An increase in the rate of serious arterial adverse events has, for example, been observed in VTE patients treated with ximelagatran relative to those receiving warfarin/placebo (short-term exposure: 0.75% vs 0.26%, p < 0.05; long-term exposure: 1.70% vs 0.70%, p <or= 0.1).

CONCLUSIONS

Further clinical trials or meta-analyses are needed before we can determine whether the unexpected thromboembolic events found with newer anticoagulants can be linked to a rebound effect on treatment cessation.

INFLUENCE OF ERYTHROMYCIN ON THE PHARMACOKINETICS OF XIMELAGATRAN MAY INVOLVE INHIBITION OF P-GLYCOPROTEIN-MEDIATED EXCRETION

A pharmacokinetic interaction between erythromycin and ximelagatran, an oral direct thrombin inhibitor, was demonstrated in this study in healthy volunteers. To investigate possible interaction mechanisms, the effects of erythromycin on active transport mediated by P-glycoprotein (P-gp) in vitro in Caco-2 and P-gp-over-expressing Madin-Darby canine kidney-human multidrug resistance-1 cell preparations and on biliary excretion of melagatran in rats were studied. In healthy volunteers (seven males and nine females; mean age 24 years) receiving a single dose of ximelagatran 36 mg on day 1, erythromycin 500 mg t.i.d. on days 2 to 5, and a single dose of ximelagatran 36 mg plus erythromycin 500 mg on day 6, the least-squares mean estimates (90% confidence intervals) for the ratio of ximelagatran with erythromycin to ximelagatran given alone were 1.82 (1.64-2.01) for the area under the concentration-time curve and 1.74 (1.52-2.00) for the maximum plasma concentration of melagatran, the active form of ximelagatran. Neither the slope nor the intercept of the melagatran plasma concentration-effect relationship for activated partial thromboplastin time statistically significantly differed as a function of whether or not erythromycin was administered with ximelagatran. Ximelagatran was well tolerated regardless of whether it was administered with erythromycin. Erythromycin inhibited P-gp-mediated transport of both ximelagatran and melagatran in vitro and decreased the biliary excretion of melagatran in the rat. These results indicate that the mechanism of the pharmacokinetic interaction between oral ximelagatran and erythromycin may involve inhibition of transport proteins, possibly P-gp, resulting in decreased melagatran biliary excretion and increased bioavailability of melagatran.

New Anticoagulant Agents: Direct Thrombin Inhibitors

Decades of research have been devoted to developing effective, safe, and convenient anticoagulant agents. In recent years, much emphasis has been placed on the development of direct thrombin inhibitors (DTIs) that offer benefits over agents like heparin and warfarin including the inhibition of both circulating and clot-bound thrombin; a more predictable anticoagulant response, because they do not bind to plasma proteins and are not neutralized by platelet factor 4; lack of required cofactors, such as antithrombin or heparin cofactor II; inhibiting thrombin-induced platelet aggregation; and absence of induction of immune-mediated thrombocytopenia. Various injectable DTIs are currently available and used for many indications. In addition, research is now focusing on oral DTIs that seem promising and offer various advantages, such as oral administration, predictable pharmacokinetics and pharmacodynamics, a broad therapeutic window, no routine monitoring, no significant drug interactions, and fixed-dose administration.

Prevention of Venous Thromboembolism in the Geriatric Patient

Elderly patients immobilized because of an acute medical illness or surgery have a very high risk of developing venous thromboembolism (VTE). Aggressive pharmacologic prophylaxis is necessary and should be initiated either at admission for a medical condition or shortly after surgery. Aggressive prophylaxis may result in fewer patients developing VTE in the hospital and ultimately lead to fewer patients requiring full-dose anticoagulation for VTE. Mechanical prophylaxis can be used as an adjunct to an anticoagulant-based regimen but should only be used as primary prophylaxis when there is a contraindication, such as active bleeding. It is recommended that the clinician carefully evaluate the elderly patient's creatinine clearance and weight before prescribing anticoagulants, particularly when using fixed dosing regimens.

Comparable Pharmacokinetics and Pharmacodynamics of Melagatran in Japanese and Caucasian Volunteers after Oral Administration of the Direct Thrombin Inhibitor Ximelagatran

OBJECTIVES

Two studies were conducted to elucidate the pharmacokinetics and pharmacodynamics of melagatran after administration of the oral direct thrombin inhibitor ximelagatran to Caucasian and Japanese volunteers.

METHODS

In study 1, with a single-blind, parallel-group design, young Japanese and Caucasian male volunteers were randomised to receive four single escalating oral doses of ximelagatran (12, 24, 36 and 60mg on separate days; n = 27 per ethnic group) or placebo (n = 6 per ethnic group). In study 2, with an open-label design, elderly Japanese male volunteers (n = 12) received three single escalating oral doses of ximelagatran (12, 24 and 36mg on separate days).

RESULTS

Regardless of the ethnicity or age of the volunteers, ximelagatran given in single oral doses was rapidly absorbed and bioconverted to melagatran, and the melagatran area under the plasma concentration-time curve (AUC) and peak plasma concentration (C(max)) increased in proportion with the ximelagatran dose, with only small deviations from absolute linearity. Higher melagatran AUC and C(max) were observed in young Japanese volunteers compared with young Caucasian volunteers, and in elderly Japanese volunteers compared with young Japanese volunteers. These results appear to be attributed to weight- and age-related decreases in renal elimination of melagatran rather than to absorption of ximelagatran and formation of melagatran. The pattern of metabolites in plasma and urine was comparable between young Japanese and Caucasian volunteers, and between young and elderly Japanese volunteers. The melagatran plasma concentration-activated partial thromboplastin time (aPTT, an ex vivo coagulation time measurement used to demonstrate inhibition of thrombin) relationship did not differ significantly between young Japanese and Caucasian volunteers or between young and elderly Japanese volunteers.

CONCLUSIONS

Ethnicity does not affect the absorption of ximelagatran or the formation of melagatran or the melagatran plasma concentration-aPTT relationship. The elimination of melagatran is correlated with renal function.

Oral Anticoagulants in Development

Current anticoagulant provision is dominated by parenteral heparin and oral warfarin, which act by inhibiting several steps of the coagulation pathway indirectly. Recent research efforts have focused on the identification of small molecule inhibitors of the coagulation enzymes as novel therapies for thrombotic disorders. There has been particular success in developing nonpeptidic, orally available, small molecules to directly inhibit the key proteases, factor IIa and factor Xa. Of the new oral anticoagulants in development, the two agents in the most advanced stage are dabigatran etexilate (BIBR 1048) and rivaroxaban (BAY 59-7939), which inhibit factor IIa and factor Xa, respectively. Other agents in the early stages of development include several Xa inhibitors (LY-517717, YM150, DU-176b and apixaban [BMS-562247]), a factor IXa inhibitor (TTP889), and an orally active glycosaminoglycan enhancer (odiparcil [SB-424323]), which indirectly enhances thrombin inhibition via heparin cofactor II. Results have been reported from important, phase II dose-finding studies, and a number of registration-track phase III studies have been initiated, reflecting the drive towards potentially more effective, but primarily safer and more convenient therapies for the prevention and treatment of venous and arterial thrombosis. Indeed, two unmet needs for anticoagulation that can be easily identified are safety and ease of use. Safety relates primarily to the incidence of major bleeding and this remains the key concern of orthopaedic surgeons, over and above any efficacy advantage, and convenience of use, which centres on oral administration replacing the need for injections. The clinical development of these new anticoagulants is following the well tested strategy of dose-ranging and registration studies in major orthopaedic surgery, prior to development in arterial indications. There are a number of subtle issues, including the timing of the first perioperative dose, duration of prophylactic treatment and definition/assessment of study endpoints that can influence study outcome and require careful consideration when evaluating study results with new agents and in the comparison with established agents, and which are considered in this review. It is anticipated that over the next 3 years, at least one of these agents will be successfully licensed for the prevention of venous thromboembolism after major orthopaedic surgery, which will act as a springboard for the gradual replacement of current anticoagulants.

Population Pharmacokinetics of Melagatran, the Active Form of the Oral Direct Thrombin Inhibitor Ximelagatran, in Atrial Fibrillation Patients Receiving Long-Term Anticoagulation Therapy

BACKGROUND

Ximelagatran is an oral direct thrombin inhibitor for the prevention of thromboembolic disease. After oral administration, ximelagatran is rapidly absorbed and bioconverted to its active form, melagatran.

OBJECTIVE

To characterise the pharmacokinetics of melagatran in patients with nonvalvular atrial fibrillation (NVAF) receiving long-term treatment for prevention of stroke and systemic embolic events.

METHODS

A population pharmacokinetic model was developed based on data from three phase II studies (1177 plasma concentration observations in 167 patients, treated for up to 18 months) and confirmed by including data from two phase III studies (8702 plasma concentration observations in 3188 patients, treated for up to 24 months). The impact of individualised dosing on pharmacokinetic variability was evaluated by simulations of melagatran concentrations based on the pharmacokinetic model.

RESULTS

Melagatran pharmacokinetics were consistent across the studied doses and duration of treatment, and were described by a one-compartment model with first-order absorption and elimination. Clearance of melagatran was correlated to creatinine clearance, which was the most important predictor of melagatran exposure (explained 54% of interpatient variance in clearance). Total variability (coefficient of variation) in exposure was 45%; intraindividual variability in exposure was 23%. Concomitant medication with the most common long-term used drugs in the study population had no relevant influence on melagatran pharmacokinetics. Simulations suggested that dose adjustment based on renal function or trough plasma concentration had a minor effect on overall pharmacokinetic variability and the number of patients with high melagatran exposure.

CONCLUSION

The pharmacokinetics of melagatran in NVAF patients were predictable, and consistent with results from previously studied patient populations. Dose individualisation was predicted to have a low impact on pharmacokinetic variability, supporting the use of a fixed-dose regimen of ximelagatran for long-term anticoagulant therapy in the majority of NVAF patients.

New Anti-thrombotic Agents: Emphasis on Hemorrhagic Complications and Their Management

Our advanced knowledge of coagulation has led to the synthesis of novel procoagulant substances, such as recombinant activated factor VII (rFVIIa; NovoSeven, Novo Nordisk, Bagsvaerd, Denmark). Similarly, in-depth understanding of the interaction between anticoagulant proteins and their natural inhibitors has led to the synthesis of various novel anticoagulants. Novel anticoagulants are characterized by highly specific coagulation-inhibiting activities and, frequently, a complete lack of effective antidotes. This lack of antidotes is particularly important in the case of novel inhibitors with extended half-lives; for example, idraparinux may produce effective anticoagulation for as long as one week after subcutaneous administration. As novel anticoagulants complete licensing evaluations and are used in clinical practice, the likelihood of anticoagulant-associated hemorrhage will increase. This will require physicians to have an understanding of the mechanism of action of these anticoagulants, and to have an advanced degree of knowledge of the potential specific and nonspecific inhibitors of these anticoagulant agents. This paper will briefly review the biochemistry of coagulation, focusing on the complexes inhibited by currently available and novel anticoagulants. Specific and nonspecific prohemostatic agents will be reviewed and discussed. The ability of nonspecific procoagulant agents (particularly rFVIIa) to reverse the effects of novel anticoagulants will also be reviewed.

Ximelagatran: a new type of oral anticoagulant

OBJECTIVES

This assessment sought to evaluate the comparative benefit and adverse effect profile of ximelagatran, as well as the clinical issues surrounding its potential use.

METHODS

We performed a Dialog OneSearch across BIOSIS Previews, EMBASE, MEDLINE, PASCAL, and ToxFile to identify published literature. PubMed and The Cochrane Library were also searched. Gray literature was identified by searching a variety of Web sites of health technology assessment and related agencies and their associated databases. The manufacturer's Canadian office, AstraZeneca, was invited to submit information.

RESULTS

Ximelagatran is the first oral agent from a new class of anticoagulants called direct thrombin inhibitors. Other oral anticoagulants require routine blood monitoring; ximelagatran does not. Ximelagatran has been evaluated in the areas of venous thromboembolism management, particularly after orthopedic surgery, and stroke prevention in patients with atrial fibrillation. Overall, ximelagatran's efficacy appears comparable to other anticoagulants in these clinical settings. Also, bleeding rates were generally similar between ximelagatran and comparators but, as for warfarin, bleeding risk increases with higher ximelagatran doses. In addition, there is no specific antidote to help manage ximelagatran-induced bleeding. Finally, significantly more patients exposed to long-term ximelagatran developed elevated liver enzymes more than three times the upper normal limit, compared with patients on comparator anticoagulants.

CONCLUSIONS

Given its apparent simplicity of use, ximelagatran carries the potential to replace, at least in part, anticoagulants currently used in the management of venous thromboembolism or for preventing stroke in atrial fibrillation patients. However, the safety of ximelagatran will not be fully known without further evaluation and surveillance for potential liver toxicity. There is also a need to evaluate its use in special populations such as patients with renal failure and patients using several concurrent medications.

BAY 59-7939: an oral, direct factor Xa inhibitor for the prevention of venous thromboembolism in patients after total knee replacement. A phase II dose-ranging study

BACKGROUND

BAY 59-7939, a novel, oral, direct factor Xa inhibitor, is in clinical development for the prevention of venous thromboembolism (VTE), a frequent complication following orthopaedic surgery.

METHODS

In a multicenter, parallel-group, double-blind, double-dummy study, 621 patients undergoing elective total knee replacement were randomly assigned to oral BAY 59-7939 (2.5, 5, 10, 20, and 30 mg b.i.d., initiated 6-8 h postsurgery), or subcutaneous enoxaparin (30 mg b.i.d., initiated 12-24 h postsurgery). Treatment was continued until mandatory bilateral venography 5-9 days after surgery. The primary efficacy endpoint was a composite of any deep vein thrombosis (proximal and/or distal), confirmed non-fatal pulmonary embolism and all-cause mortality during treatment. The primary safety endpoint was major, postoperative bleeding during treatment.

RESULTS

Of the 613 patients treated, 366 (59.7%) were evaluable for the primary efficacy analysis. The primary efficacy endpoint occurred in 31.7%, 40.4%, 23.3%, 35.1%, and 25.4% of patients receiving 2.5, 5, 10, 20 and 30 mg b.i.d. doses of BAY 59-7939, respectively (test for trend, P = 0.29), compared with 44.3% in the enoxaparin group. The frequency of major, postoperative bleeding increased with increasing doses of BAY 59-7939 (test for trend, P = 0.0007), with no significant difference between any dose group compared with enoxaparin. Bleeding endpoints were lower for the 2.5-10 mg b.i.d. doses compared with higher doses of BAY 59-7939.

CONCLUSIONS

Oral administration of 2.5-10 mg b.i.d. of BAY 59-7939, early in the postoperative period, showed potential efficacy and an acceptable safety profile, similar to enoxaparin, for the prevention of VTE in patients undergoing elective total knee replacement.

Update on the diagnosis and management of pulmonary embolism

Pulmonary embolism (PE) is a common and often fatal disease. In the US, an estimated 40-53 people per 100,000 are diagnosed with PE annually and approximately 60,000 die from the disease. Diagnosis is difficult because symptoms are non-specific; however, a quick and accurate diagnosis is critical because, with appropriate therapy, the risk of recurrent (and potentially fatal) PE can be greatly reduced. Recent publication of prediction rules and improved non-invasive diagnostic tools have simplified diagnostic algorithms for PE. The efficacy of the standard treatment for PE, initial administration of continuous i.v. unfractionated heparin overlapped with long-term oral anticoagulation, is well established. However, newer treatment options such as low-molecular-weight heparins and the pentasaccharides may offer similar efficacy with improved convenience.

Meta-analysis of trials comparing ximelagatran with low molecular weight heparin for prevention of venous thromboembolism after major orthopaedic surgery

Background

Use of low molecular weight heparin (LMWH) is standard practice for preventing postoperative venous thromboembolism (VTE). Ximelagatran is a new direct thrombin inhibitor for this indication.

Methods

A systematic review was conducted to compare the efficacy and safety of LMWH with ximelagatran in orthopaedic surgery.

Results

Six eligible, well conducted clinical trials (10 051 patients) were identified. Overall, the risk of VTE (OR (odds ratio) 1·22 (95 per cent confidence interval (c.i.) 0·89 to 1·67)) and serious bleeding (OR 0·70 (95 per cent c.i. 0·42 to 1·18)) was not significantly different for LMWH compared with ximelagatran. Exploratory analyses to investigate statistical heterogeneity found that results varied by surgical subtype and treatment regimen. Compared with postoperative ximelagatran, LMWH had a significantly lower rate of VTE (OR 0·68 (95 per cent c.i. 0·56 to 0·82); P &lt; 0·001), with no significant difference in bleeding rate (OR 1·09 (95 per cent c.i. 0·62 to 1·94); P = 0·76), in hip surgery, and no significant differences in knee surgery. When ximelagatran was started immediately before surgery, LMWH had a significantly higher rate of VTE in both hip (OR 1·87 (95 per cent c.i. 1·20 to 2·92); P = 0·006) and knee (OR 1·49 (95 per cent c.i. 1·14 to 1·93); P = 0·003) surgery, but less bleeding: hip OR 0·30 (95 per cent c.i. 0·17 to 0·53; P &lt; 0·001); knee OR 0·71 (95 per cent c.i. 0·30 to 1·67; P = 0·43).

Conclusion

This review demonstrated no overall advantage for either LMWH or ximelagatran in thromboprophylaxis following orthopaedic surgery. Benefits in VTE prevention with ximelagatran were gained at the expense of an increased risk of serious bleeding.

The Antithrombotic Effect of Melagatran in Combination With Clopidogrel and/or Aspirin (carotid artery primary thrombosis study)

Melagatran with aspirin and/or clopidogrel was evaluated for prevention of arterial thrombosis in a model of vessel wall injury. Thirty-five dogs were randomized to receive placebo (n=14), aspirin (7 to 8 mg/kg, p.o. q12 h for three doses with the last dose administered 12 hours before surgery, n=7), clopidogrel (1 mg/kg p.o. QDx3, n=7), or aspirin+clopidogrel (n=7). The right carotid artery (RCA) was the control vessel, whereas the left carotid artery (LCA) was subjected to injury after administration of Melagatran (0.033 mg/kg i.v.+0.1 mg/kg/h). Clopidogrel, but not aspirin pretreatment, increased time (135.6+/-13.5 vs. 116.1+/-27.8 minutes) to RCA thrombosis versus placebo (88.1+/-10.5 minutes). Melagatran prolonged time to occlusion (min) in the LCA (192.4+/-10.9) versus the placebo-treated RCA (88.1+/-10.5). Addition of Melagatran plus aspirin or clopidogrel prevented formation of occlusive thrombosis, in all LCAs. A two-fold increase in tongue bleeding time was observed after aspirin+Melagatran (178.6+/-14.7 to 347.1+/-87.3 seconds) or clopidogrel+Melagatran (279.9+/-97.3 to 437.1+/-142.5 seconds). However, the combination of aspirin and clopidogrel prevented occlusive thrombosis in the RCA and the subsequent addition of Melagatran did not further increase bleeding time. The combination of Melagatran+aspirin or clopidogrel can reduce formation of occlusive arterial thrombosis without eliciting a significant increase in bleeding-time.

New antithrombotics in the prevention of thromboembolic disease

New anticoagulants are under development to improve on current ones that, although effective, have limitations in efficacy, safety and convenience. We have reviewed the use of these agents as thromboprophylactic drugs. These new agents have more specific modes of action and can be divided into three groups. Inhibitors of the initiation of coagulation work via inhibition of the factor VIIa/tissue factor complex. Inhibitors of propagation of coagulation include parenteral and oral factor Xa inhibitors, factor IXa inhibitors, inhibitors of factor Va and VIIIa, activated Protein C, soluble thrombomodulin and SNAC-Heparin. Finally, direct inhibitors of thrombin are under development both for parenteral and oral administration. Several new drugs, such as fondaparinux, hirudin, argatroban, bivalirudin and ximelagatran, have already been licensed for specific indications and are being investigated for more general usage. Other drugs reviewed are in much earlier stages of development.

New antithrombotics in the treatment of thromboembolic disease

New insights into the in vivo function of the coagulation system have resulted in the development of new antithrombotic agents with a more specific point of impact and more reliable pharmacological properties. Inhibition of coagulation can be achieved by specific thrombin inhibitors (e.g. melagatran), agents specifically targeted at factor Xa (e.g. pentasaccharides), and by tissue factor/factor VIIa blockers (e.g. recombinant NAPc2). In some situations, these agents are more effective and safer than the antithrombotics currently used. However, the major difference may be that the newer generation of antithrombotics does not require repeated laboratory control and dose adjustment to obtain a stable level of anticoagulation; therefore, they are more suitable for application in clinical practice. In this overview, we will briefly discuss the various new compounds that have recently become available or that will be introduced into clinical medicine in the near future and their relative efficacy and safety in comparison to currently used antithrombotic agents.

Prévention de la maladie thromboembolique en orthopédie et traumatologie

Orthopaedic and trauma surgery are classified according 3 groups of venous thromboembolic risk. Elective total hip replacement (THR) or total knee replacement (TKR), hip fracture surgery or trauma patients are at high risk. Isolated lower extremity injury with fracture is at moderate risk whereas this risk is low without fracture as well as with knee arthroscopy. In THR and TKR, low molecular weight heparin (LMWH), fondaparinux or melagatran-ximelagatran are strongly recommended. The routine use of other anticoagulants, in particular vitamin K antagonist are not recommended. In patients at high risk of venous thromboembolism as for example trauma patients, optimal use of intermittent pneumatic compression is an alternative option in case of contra-indication to anticoagulant prophylaxis. Graduated compression stockings enhance the efficacy of pharmacological methods. In schedule surgery, initiation of prophylaxis with LMWH may be started postoperatively. To reduce the haemorrhagic risk of anticoagulants, timing of first postoperative dose is essential and is proper to each drug. Duration of prophylaxis depends on the surgical and the individual patients' risk. Extended prophylaxis in THR for up to 42 days with LMWH and up to 35 days with fondaparinux in hip fracture surgery is recommended. However extended prophylaxis after 14 days in TKR has not demonstrated a higher efficacy and should only be considered for patients with additional risk factors. In patients with isolated lower extremity injury or undergoing knee arthroscopy, LMWH should not be routinely used according to a low or a moderate risk and/or the duration of prophylaxis required. But LMWH has to be considered for patients with additional risk factors. Prophylaxis in other orthopedic procedures has not been assessed and will be extrapolated from the above recommendations.

Ximelagatran: a clinical perspective

Ximelagatran is a novel oral anticoagulant belonging to a class of drugs known as direct thrombin inhibitors. Numerous recent large-scale, randomised controlled clinical trials have given the drug a large clinical platform. These include data on the thromboprophylaxis of venous thromboembolism following major orthopaedic surgery and knee arthroscopy, as well as in the treatment of deep vein thrombosis and prevention of stroke with nonvalvular atrial fibrillation. One phase II study has also shown the efficacy and safety of ximelagatran in secondary prevention post-myocardial infarction. Unfortunately, approximately 6% of patients develop usually self-limiting derangement of liver dysfunction, and frequent monitoring of liver function is likely to be recommended for the first 6 months of treatment. Unlike the vitamin K antagonists, ximelagatran has a wide therapeutic interval with few food, alcohol or drug interactions, and it does not require anticoagulant monitoring. The aim of this overview is to review the clinical trials pertaining to this new drug, which is the first new oral anticoagulant for over 60 years, and one that is likely to influence our management of thrombosis-related disorders.

[What kind of treatment are available in deep vein thrombosis prevention?]

In order to propose new recommendations concerning deep vein thrombosis prevention in surgery and obstetrics, we identified all the available tools. We performed a Medline search for ten years to review all the studies published in this field. This preliminary stage is mandatory in assessing guidelines able to work out strategies considering each patient in each particular surgical situation. There are no formal guidelines and we outlined a practical approach for the prevention of deep vein thrombosis. Data concerning all available treatment were not classified in an evidence-based strategy.

New anticoagulant therapy

The development of new anticoagulants is expanding the list of drugs that can be used to prevent and treat venous and arterial thrombosis. New parenteral anticoagulants have been developed to overcome the limitations of heparin and low-molecular-weight heparin, whereas novel orally active anticoagulants have been designed to provide more streamlined therapy than vitamin K antagonists. This review identifies the molecular targets of new anticoagulants, describes the results of clinical trials, and provides clinical perspective on the opportunities for new anticoagulants.

Ximelagatran: An orally active direct thrombin inhibitor

PURPOSE

The chemistry, pharmacology, pharmacokinetics, clinical efficacy, dosage and administration, contraindications, and adverse effects of ximelagatran are reviewed.

SUMMARY

Ximelagatran is the first orally active direct thrombin inhibitor to be tested in Phase III clinical trials. After oral administration, ximelagatran is rapidly converted to its active metabolite, melagatran. Melagatran (after oral ximelagatran administration) predictably inhibits thrombin function without need for routine anticoagulation monitoring. Melagatran effectively inhibits both free and clot-bound thrombin-a potential pharmacodynamic advantage over heparin products. Melagatran has a half-life of 2.4-4.6 hours, necessitating twice-daily administration. Melagatran is primarily eliminated by the kidneys and has not been studied clinically in patients with severe renal failure. Ximelagatran has undergone 10 Phase III trials (6 for prophylaxis of venous thromboembolism [VTE] due to orthopedic surgery, 1 for initial treatment of VTE, 1 for long-term prevention of VTE recurrence, and 2 for stroke prophylaxis due to atrial fibrillation). Results were generally positive. AstraZeneca applied in December 2003 for marketing approval of ximelagatran for prevention of VTE after total knee replacement surgery, long-term prevention of VTE recurrence after standard therapy, and stroke prevention due to atrial fibrillation. FDA denied approval of ximelagatran for all indications, mainly because of increased rates of coronary artery disease events in ximelagatran recipients in some studies and the possibility of hepatic failure when the medication is used for long-term therapy.

CONCLUSION

Ximelagatran has shown promise as a possible alternative to warfarin and other anticoagulants but will require further study to ensure its safety.

No effect of encapsulation on the pharmacokinetics of warfarin

BACKGROUND

In double-blind comparator studies with the oral direct thrombin inhibitor (oral DTI) ximelagatran, warfarin (Coumadin) was administered in encapsulated form in order to maintain patient and investigator blinding. This open, randomized, two-way crossover study was conducted to determine whether the encapsulated warfarin tablets (Coumadin) used in the ximelagatran studies are bioequivalent to nonencapsulated, commercially available warfarin (Coumadin) tablets.

METHODS AND RESULTS

Eighteen healthy men received two 2.5 mg tablets of encapsulated warfarin and two 2.5 mg tablets of nonencapsulated warfarin as single oral doses, 14 days apart. The 90% confidence intervals for the mean treatment ratio (encapsulated tablet/nonencapsulated tablet) fell within the limits considered to reflect bioequivalence (0.80, 1.25) for total area under the plasma concentration-versus-time curve (AUC(infinity)), AUC to the last evaluable concentration (AUC(t)), and maximum plasma concentration (C(max)) for both R-warfarin (AUC(infinity) [0.93, 1.03], AUC(t) [0.95, 1.03], C(max) [0.90, 1.04]) and S-warfarin (AUC(infinity) [0.93, 1.03], AUC(t) [0.94, 1.03], C(max) [0.90, 1.06]).

CONCLUSIONS

The encapsulated form of warfarin (Coumadin) used in comparator studies with the oral DTI ximelagatran is bioequivalent to the nonencapsulated, commercially available form of warfarin (Coumadin). Thus, the results of ximelagatran clinical trials with encapsulated warfarin can be generalized to the commercially available form.

A review of the oral direct thrombin inhibitor ximelagatran: not yet the end of the warfarin era

Ximelagatran is a direct thrombin inhibitor that offers numerous potential advantages compared with traditional anticoagulants. It is given orally, has a rapid onset of action, does not require laboratory monitoring, and is not associated with immune-mediated thrombocytopenia. Numerous phase III trials with ximelagatran focusing on deep vein thrombosis prophylaxis and treatment, stroke prevention in patients with atrial fibrillation, and secondary prevention after acute myocardial infarction have been conducted. Results of these trials indicate that ximelagatran has similar efficacy and risk of bleeding compared with currently used anticoagulants. Accordingly, the potential of this agent to replace warfarin therapy for a variety of indications has been widely touted. Ximelagatran has already been approved in Europe for prophylaxis of venous thromboembolism in patients undergoing hip or knee surgery. However, an adverse effect of ximelagatran is liver enzyme elevation, which has been observed in 5% to 10% of patients with chronic administration of the drug. Although initially felt to be transient in nature, subsequent data presented to the Federal Drug Administration suggest a small but real risk of significant hepatotoxicity. These data led the advisory committee to the Federal Drug Administration to recommend against immediate approval of ximelagatran pending further information. The consistent results of completed trials with ximelagatran suggest that it has the potential to be used in many conditions that currently require treatment with warfarin and heparin products. The potential benefit that may be achieved by the replacement of these historically problematic narrow therapeutic index agents must be weighed against as yet undetermined long-term risks of hepatotoxicity.

Acute pulmonary embolism: an update on diagnosis and management

Pulmonary embolism (PE) is a common problem. Given the significant overlap of symptoms and signs between the presentation of PE and acute coronary syndromes, it becomes clear that cardiologists must be familiar with the diagnosis and treatment of PE. The critical issue is always to consider PE in the diagnosis of chest pain. It is then important to determine the likelihood of the diagnosis. For patients at moderate-to-high risk, helical CT provides a rapid and noninvasive diagnostic tool. Several other imaging studies are also available including ventilation/perfusion (V/Q) scan, magnetic resonance imaging, and pulmonary arteriography. Echocardiography can also provide valuable prognostic information. Several biomarkers including the d-dimers, troponins, and natriuretic peptides may provide additional information. The cornerstone of treatment includes anticoagulation. For patients with massive or submassive PE, thrombolysis and embolectomy should be considered. Finally, both primary and secondary prevention are critical to the long-term health of the patient.

The effects of ximelagatran and warfarin on the prophylaxis of a caval vein thrombosis and bleeding in the anaesthetized rat

The antithrombotic and bleeding properties of the oral direct thrombin inhibitor ximelagatran and of warfarin were investigated in an experimental venous thrombosis and bleeding model in anaesthetized rats. Rats were randomized to receive ximelagatran (1-20 micromol/kg), warfarin (0.20-0.82 micromol/kg), or vehicle (tap water) once daily orally for 4 days before surgery. Thrombosis was induced by partial stenosis and application of ferric chloride to the wall of the abdominal vena cava under anaesthesia. Sixty minutes after thrombus induction, rats were sacrificed, thrombi harvested, and their fresh weight determined. Bleeding was determined as haemoglobin in fluid collected from the abdominal cavity. Blood samples were taken before thrombus induction and sacrifice for determination of coagulation parameters and plasma concentrations of melagatran, the active form of ximelagatran. Ximelagatran and warfarin dose-dependently reduced thrombus formation. The highest doses of ximelagatran and warfarin almost completely prevented thrombus formation; however, the increase in bleeding (versus vehicle) was significantly lower with the highest dose of ximelagatran than with the highest dose of warfarin. The oral direct thrombin inhibitor ximelagatran is thus as at least as effective as warfarin in the prevention of thrombus formation in this animal model, but with a wider separation between antithrombotic effects and bleeding.

The role of oral direct thrombin inhibitors in the prophylaxis of venous thromboembolism

Venous thromboembolism, which is manifested as deep vein thrombosis (DVT) and pulmonary embolism (PE), represents a significant cause of death, disability, and discomfort. Two million people/year are affected by VTE, making it the third most common cardiovascular disease after coronary heart disease and stroke. The rationale for VTE prophylaxis stems from the clinically silent presentation of the disease and its prevalence among hospitalized patients. At greatest risk are patients undergoing major orthopedic surgery and those admitted to the intensive care unit with acute myocardial infarction, heart failure, ischemic stroke, respiratory disease, systemic infection, or other medical conditions that immobilize patients for 5 days or longer. Several anticoagulant regimens have been effective in reducing the risk of VTE after major orthopedic surgery. For patients undergoing total hip or knee replacement, treatment with adjusted-dose warfarin, low-molecular-weight heparins, or fondaparinux may be used. Warfarin, which has been around for more than 50 years, is the only oral anticoagulant available for VTE prophylaxis. Ximelagatran, a new low-molecular-weight oral prodrug of the direct thrombin inhibitor melagatran, has advantages over warfarin that may make it the drug of choice for prevention of VTE.