Comparison of ximelagatran, an oral direct thrombin inhibitor, with enoxaparin for the prevention of venous thromboembolism following total hip replacement. A randomized, double-blind study

Statistical Fragility of Venous Thromboembolism Prophylaxis Following Total Joint Arthroplasty

Background

Statistical fragility is a quantitative measure of the robustness of the statistical conclusions drawn in a study. Although statistical fragility has been comprehensively evaluated in the arthroplasty literature, the statistical fragility of large-scale randomized trials evaluating venous thromboembolism (VTE) prophylaxis has not been evaluated. The purpose of this study was to determine the utility of applying the fragility index (FI) and the fragility quotient (FQ) analysis to randomized controlled trials (RCTs) evaluating VTE prophylaxis following total joint arthroplasty.

Methods

A systematic review was performed by searching multiple databases to identify RCTs that evaluated VTE prophylaxis following total joint arthroplasty from 2000 to 2020. The FI was determined by manipulating each reported dichotomous outcome event until a reversal of significance was appreciated with 2 × 2 contingency tables. The associated FQ was determined by dividing the FI by the sample size.

Results

Thirty-two RCTs were ultimately included for analysis. The overall FI incorporating all 32 RCTs was only 7 (interquartile range 3-9), suggesting that the reversal of only 7 events is required to change study significance. The associated FQ was determined to be 0.01. Of the RCTs that reported lost-to-follow-up data, the majority of studies had lost-to-follow-up numbers greater than 7.

Conclusions

Our findings suggest that RCTs evaluating VTE prophylaxis following total hip arthroplasty and total knee arthroplasty may lack statistical stability as few outcome events are required to reverse the significance of outcomes. Future randomized trials should consider reporting FI and FQ along with the P value analysis to provide better context to the integrity of statistical stability.

Efficacy and safety of anticoagulants for postoperative thrombophylaxis in total hip and knee arthroplasty: A PRISMA-compliant Bayesian network meta-analysis

Objective

To search, review, and analyze the efficacy and safety of various anticoagulants from randomized clinical trials (RCTs) of anticoagulants for THA and TKA.

Design

PRISMA-compliant Bayesian Network Meta-analysis.

Data sources and study selection

The databases of The Medline, Embase, ClinicalTrial, and Cochrane Library databases were searched until March 2017 for RCTs of patients undergoing a THA or TKA.

Main outcomes and measures

The primary efficacy measurement was the venous thromboembolism Odds ratio (OR). The safety measurement was the odds ratio of major or clinically relevant bleeding. OR with 95% credibility intervals (95%CrIs) were calculated. Findings were interpreted as associations when the 95%CrIs excluded the null value.

Results

Thirty-five RCTs (53787 patients; mean age range, mostly 55–70 years; mean weight range, mostly 55–90 kg; and a higher mean proportion of women than men, around 60%) included the following Anticoagulants categories: fondaparinux, edoxaban, rivaroxaban, apixaban, dabigatran, low-molecular-weight heparin, ximelagatran, aspirin, warfarin. Anticoagulants were ranked for effectiveness as follows: fondaparinux (88.89% ± 10.90%), edoxaban (85.87% ± 13.34%), rivaroxaban (86.08% ± 10.23%), apixaban (68.26% ± 10.82%), dabigatran (41.63% ± 12.26%), low-molecular-weight heparin (41.03% ± 9.60%), ximelagatran (37.81% ± 15.87%), aspirin (35.62% ± 20.60%), warfarin (9.89% ± 9.07%), and placebo (4.56% ± 6.37%). Ranking based on clinically relevant bleeding events was as follows: fondaparinux (14.53% ± 15.25%), ximelagatran (18.93% ± 17.49%), rivaroxaban (23.86% ± 15.14%), dabigatran (28.30% ± 14.18%), edoxaban (38.76% ± 24.25%), low-molecular-weight heparin (53.28% ± 8.40%), apixaban (71.81% ± 10.92%), placebo (76.26% ± 14.61%), aspirin (86.32% ± 25.74%), and warfarin (87.95% ± 11.27%). No statistically significant heterogeneity was observed between trials.

Conclusions and relevance

According to our results, all anticoagulant drugs showed some effectiveness for VTE prophylaxis. Our ranking indicated that fondaparinux and rivaroxaban were safer and more effective than other anticoagulant drugs for patients undergoing THA or TKA.

Ranking the efficacy of anticoagulants for the prevention of venous thromboembolism after total hip or knee arthroplasty: A systematic review and a network meta-analysis

BACKGROUND

Anticoagulants are essential in the prevention of venous thromboembolism. However, the effectiveness and safety of different anticoagulants have always been controversial. Therefore, we aimed to expand the sample of anticoagulant results and rank the efficacy and safety of 19 anticoagulants in the prevention of venous thromboembolism when total knee or total hip arthroplasty procedure is performed.

METHODS

A systematic review and network meta-analysis of randomized trials of adult patients undergoing total hip or knee arthroplasty were conducted. The trials were identified from PubMed, Web of Science, Cochrane Library, and Embase databases, in which anticoagulants were used as interventions randomized controlled trial. The incidence of venous embolism and bleeding are the key outcomes of assessing the efficacy of intervention drugs. We used the Physical Therapy Evidence Database (PEDro) to assess risk bias and used pairwise comparison and network meta-analysis with random effects to estimate the summary relative risk. The study has been registered with PROSPERO, number CRD42020200747.

RESULTS

From the 4083 identified manuscripts, 45,067 participants from 53 randomized trials were included in the analysis and randomly assigned to 19 anticoagulants. With Enoxaparin as a control, Rivaroxaban (risk difference 0.07, 95 % credible interval 0.06 to 0.08), Edoxaban (RD 0.09, 95 % CrI 0.08 to 0.11), and Apixaban (RD 0.05, 95 % CrI 0.04 to 0.06) had the best effect in preventing VTE. However, in terms of comprehensive bleeding rate, Apixaban, Edoxaban, and Darexaban were the most effective and stable. Although effective in preventing VTE, bleeding remains relatively high in Rivaroxaban. Enoxaparin is low-molecular-weight heparin that is widely used in clinics, and although its overall efficacy is not the best, its efficacy and safety are very stable.

CONCLUSION

According to the available data, Apixaban, Edoxaban, and Darexaban are better than any anticoagulants in the prevention of VTE and bleeding during total knee or total hip arthroplasty. In our study, Fondaparinux, Eribaxaban, Dalteparin, Betrixaban, Bemiparin, Reviparin, Acenocoumarol, and Tinzaparin were scarce in the included studies, therefore, more evidence is needed to prove their efficacy and safety.

Factor Xa Inhibitors and Direct Thrombin Inhibitors Versus Low-Molecular-Weight Heparin for Thromboprophylaxis After Total Hip or Total Knee Arthroplasty: A Systematic Review and Meta-Analysis

BACKGROUND

The purpose of this study is to perform a meta-analysis to compare outcomes of venous thromboembolism (VTE) prophylaxis with low-molecular-weight heparin (LMWH) vs other anticoagulants in patients who received total knee (TKA) or total hip arthroplasty (THA).

METHODS

MEDLINE, Cochrane, EMBASE, and Google Scholar databases were searched until June 30, 2017 for eligible randomized controlled studies.

RESULTS

Thirty-two randomized controlled studies were included. LMWH provided better protection against VTE than placebo. In both TKA and THA patients, the rates of VTE were lower with factor Xa inhibitors than LMWH. In THA patients, the rate of deep vein thrombosis (DVT) was lower with factor Xa inhibitors than LMWH. In TKA patients, the rates of VTE and DVT were similar between LMWH and direct thrombin inhibitors. In THA patients, the rate of VTE was lower with direct thrombin inhibitors than with LMWH, while the DVT rates were similar. The pulmonary embolism rates were similar between all 3 classes of drugs in TKA and THR patients, as were the major bleeding rates. Nonmajor and minor bleeding rates were also similar between the 3 drug classes.

CONCLUSION

LMWH is associated with a higher rate of VTE than factor Xa inhibitors in TKA and THA patients. Direct thrombin inhibitors are associated with a lower rate of VTE in THA patients, but their effectiveness with respect to DVT and pulmonary embolism prophylaxis is similar to that of LMWH in TKA and THA patients.

Low molecular weight heparin versus other anti-thrombotic agents for prevention of venous thromboembolic events after total hip or total knee replacement surgery: a systematic review and meta-analysis

Background

Venous thromboembolism (VTE) is an important complication following total hip replacement (THR) and total knee replacement (TKR) surgeries. Aim of this study was to comprehensively compare the clinical outcomes of low-molecular-weight heparin (LMWH) with other anticoagulants in patients who underwent TKR or THR surgery.

Methods

Medline, Cochrane, EMBASE, and Google Scholar databases were searched for eligible randomized controlled studies (RCTs) published before June 30, 2017. Meta-analyses of odds ratios were performed along with subgroup and sensitivity analyses.

Results

Twenty-one RCTs were included. In comparison with placebo, LMWH treatment was associated with a lower risk of VTE and deep vein thrombosis (DVT) (P values < 0.001) but similar risk of pulmonary embolism (PE) (P = 0.227) in THR subjects. Compared to factor Xa inhibitors, LMWH treatment was associated with higher risk of VTE in TKR subjects (P < 0.001), and higher DVT risk (P < 0.001) but similar risk of PE and major bleeding in both THR and TKR. The risk of either VTE, DVT, PE, or major bleeding was similar between LMWH and direct thrombin inhibitors in both THR and TKR, but major bleeding was lower with LMWH in patients who underwent THR (P = 0.048).

Conclusion

In comparison with factor Xa inhibitors, LMWH may have higher risk of VTE and DVT, whereas compared to direct thrombin inhibitors, LMWH may have lower risk of major bleeding after THR or TKR.

Electronic supplementary material

The online version of this article (10.1186/s12891-018-2215-3) contains supplementary material, which is available to authorized users.

Indirect comparison meta-analysis of two enoxaparin regimens in patients undergoing major orthopaedic surgery

Two enoxaparin dosage regimens are used as comparators to evaluate new anticoagulants for thromboprophylaxis in patients undergoing major orthopaedic surgery, but so far no satisfactory direct comparison between them has been published. Our objective was to compare the efficacy and safety of enoxaparin 3,000 anti-Xa IU twice daily and enoxaparin 4,000 anti-Xa IU once daily in this clinical setting by indirect comparison meta-analysis, using Bucher’s method. We selected randomised controlled trials comparing another anticoagulant, placebo (or no treatment) with either enoxaparin regimen for venous thromboembolism prophylaxis after hip or knee replacement or hip fracture surgery, provided that the second regimen was assessed elsewhere versus the same comparator. Two authors independently evaluated study eligibility, extracted the data, and assessed the risk of bias. The primary efficacy outcome was the incidence of venous thomboembolism. The main safety outcome was the incidence of major bleeding. Overall, 44 randomised comparisons in 56,423 patients were selected, 35 being double-blind (54,117 patients). Compared with enoxaparin 4,000 anti-Xa IU once daily, enoxaparin 3,000 anti-Xa IU twice daily was associated with a reduced risk of venous thromboembolism (relative risk [RR]: 0.53, 95% confidence interval [CI]: 0.40 to 0.69), but an increased risk of major bleeding (RR: 2.01, 95% CI: 1.23 to 3.29). In conclusion, when interpreting the benefit-risk ratio of new anticoagulant drugs versus enoxaparin for thromboprophylaxis after major orthopaedic surgery, the apparently greater efficacy but higher bleeding risk of the twice-daily 3,000 anti-Xa IU enoxaparin regimen compared to the once-daily 4,000 anti-Xa IU regimen should be taken into account.

Effects of different anticoagulant drugs on the prevention of complications in patients after arthroplasty: A network meta-analysis

BACKGROUND

After arthroplasty treatment, some complications commonly occur, such as early revision, infection/dislocation, and venous thromboembolism (VTE). This study aims to use a network meta-analysis to compare effects of 9 anticoagulant drugs (edoxaban, dabigatan, apixaban, rivaroxaban, warfarin, heparin, bemiparin, ximelagatran, and enoxaparin) in preventing postoperative complications in arthroplasty patients.

METHODS

After retrieving PubMed, Embase, and Cochrane Library database from the inception to November 2016, randomized controlled trials were enrolled. The integration of direct and indirect evidences was performed to calculate odd ratios and the surface under the cumulative ranking curves. Nineteen eligible randomized controlled trials were included.

RESULTS

The network meta-analysis results showed that compared with warfarin, edoxaban, apixaban, and rivaroxaban had a lower incidence rate in asymptomatic deep venous thrombosis, which indicated that edoxaban, apixaban, and rivaroxaban had better effects on prevention. Similarly, in comparison to enoxaparin, edoxaban and rivaroxaban had better effect; rivaroxaban was better than ximelagatran in preventive effects. Compared with apixaban, edoxaban, dabigatan, rivaroxaban, and enoxaparin had a higher incidence rate in clinically relevant non-major bleeding, which showed that preventive effects were relatively poor. In addition, the results of the surface under the cumulative ranking curves showed that rivaroxaban and bemiparin worked best on symptomatic deep venous thrombosis and pulmonary embolism. In terms of bleeding, apixaban and warfarin had better preventive effects.

CONCLUSION

Our findings suggested that rivaroxaban may work better in terms of symptomatic deep venous thrombosis and pulmonary embolism, whereas apixaban had better preventive effects in bleeding.

Pulmonary Embolism Rates Following Total Hip Arthroplasty With Prophylactic Anticoagulation: Some Pulmonary Emboli Cannot Be Avoided

BACKGROUND

A symptomatic pulmonary embolism (PE) after total joint arthroplasty has been described as a "never event." Despite potent anticoagulants and improvements in patient care, PE continues to occur following total hip arthroplasty (THA). This study evaluates symptomatic PE rates over time in THA patients enrolled in multicenter randomized clinical trials (RCTs) assessing the efficacy of venous thromboembolism prophylaxis regimens.

METHODS

The MEDLINE and Cochrane Central Register of Controlled Trials were searched to identify clinical trials assessing prophylactic anticoagulation in patients undergoing THA between January 1995 and December 2015. Inclusion criteria consisted of RCTs evaluating prophylactic anticoagulation in patients undergoing THA. A random effect model was used to combine PE rates across studies.

RESULTS

A total of 21 studies (34,764 patients) were included. Patients were administered low molecular weight heparin (13,590 patients), oral factor Xa inhibitors (6609 patients), oral direct thrombin inhibitors (5965 patients), indirect factors Xa/IIa inhibitors (3444 patients), aspirin (2427 patients), and warfarin (489 patients). Mobile compression was used in 199 patients, and placebo was used in 2041 patients. Across all included studies, the estimated PE rate was 0.21% (95% confidence interval: 0.13%, 0.32%). Between 1997 and 2013, the proportion of PEs did not change in regression analysis.

CONCLUSION

Although the PE rate was low, it was consistent throughout the 17 years spanning these RCTs, which excluded patients with significant morbidity. These results suggest that even healthy THA patients receiving aggressive anticoagulation still have a risk for PE, and the "never event" designation requires reassessment.

The Future of Anticoagulation

Anticoagulant agents, such as unfractionated heparin and warfarin, have been in use for roughly 50 years. Over the past decade, injectable agents such as low-molecular-weight heparins, pentasaccharide, and direct thrombin inhibitors have been major advances in preventing and treating thrombosis. Despite these somewhat recent additions, there is still enormous potential to improve on the pharmacokinetic and pharmacodynamic properties of these agents, as well as improve patient outcomes. There are currently a large number of anticoagulant agents (injectable and oral) that could be available for use in the next several years. Many of these new agents have unique mechanisms that may provide practitioners with anticoagulant alternatives. This review gives a detailed analysis of the anticoagulant agents that may add to our armamentarium in the management of thrombosis.

Ximelagatran for stroke prevention in atrial fibrillation

Atrial fibrillation is the most common sustained cardiac arrhythmia and the most frequently encountered cause of embolic stroke. Vitamin K antagonists (such as warfarin) have represented the cornerstone of anticoagulation practice for the last 60 years. Although highly effective in preventing thromboembolic events among patients with atrial fibrillation, warfarin therapy is limited by a multitude of potential problems. Hence, warfarin is significantly underused in clinical practice, with only half of warfarin-treated patients actually achieving therapeutic anticoagulation in routine clinical practice. Consequently, there is an overwhelming need for an alternative oral anticoagulant for patients with atrial fibrillation that is safer, more practical and effective. Ximelagatran (Exanta, AstraZeneca) is a novel oral direct thrombin inhibitor that is rapidly converted to the active compound melagatran after oral absorption. It has a low potential for drug interactions, anticoagulation monitoring is not required, and it is administered at a fixed twice-daily dose. The Stroke Prevention using the ORal Thrombin Inhibitor in patients with nonvalvular atrial Fibrillation (SPORTIF) III and V trials have together demonstrated the noninferiority of ximelagatran relative to warfarin for the prevention of stroke and embolic events in atrial fibrillation. Unfortunately, initial optimism has been tempered by serious concerns over its safety data in view of its propensity to cause elevation in liver enzymes.

A Preliminary Assessment of the Critical Differences Between Novel Oral Anticoagulants Currently in Development

Chronic anticoagulation represents a clinical conundrum for the health care community that balances unquestionable morbidity and mortality benefits against interindividual variability, leading to drug interactions, adverse events, and thromoembolic events related to underdosing. Despite the growing data regarding the appropriate use and dosing of agents used for chronic anticoagulation, use in clinical practice remains low, thus leading to a theoretical reduction in the risk-to-benefit ratio in the clinical setting relative to that reported in the literature. Oral anticoagulants currently in development represent a heterogeneous group of compounds that are specific for the final common pathway in the coagulation cascade and show indications toward a reduced drug interaction profile, reduced interpatient variation in pharmacokinetic parameters, and morbidity and mortality benefits that might be similar to currently available treatment modalities. This review highlights the critical differences among oral anticoagulants in development and places their role in the context of the benefits and limitations of currently available anticoagulants.

Meta-analysis of cause of death following total joint replacement using different thromboprophylaxis regimens

We performed a meta-analysis of modern total joint replacement (TJR) to determine the post-operative mortality and the cause of death using different thromboprophylactic regimens as follows: 1) no routine chemothromboprophylaxis (NRC); 2) Potent anticoagulation (PA) (unfractionated or low-molecular-weight heparin, ximelagatran, fondaparinux or rivaroxaban); 3) Potent anticoagulation combined (PAC) with regional anaesthesia and/or pneumatic compression devices (PCDs); 4) Warfarin (W); 5) Warfarin combined (WAC) with regional anaesthesia and/or PCD; and 6) Multimodal (MM) prophylaxis, including regional anaesthesia, PCDs and aspirin in low-risk patients. Cause of death was classified as autopsy proven, clinically certain or unknown. Deaths were grouped into cardiopulmonary excluding pulmonary embolism (PE), PE, bleeding-related, gastrointestinal, central nervous system, and others (miscellaneous). Meta-analysis based on fixed effects or random effects models was used for pooling incidence data. In all, 70 studies were included (99 441 patients; 373 deaths). The mortality was lowest in the MM (0.2%) and WC (0.2%) groups. The most frequent cause of death was cardiopulmonary (47.9%), followed by PE (25.4%) and bleeding (8.9%). The proportion of deaths due to PE was not significantly affected by the thromboprophylaxis regimen (PA, 35.5%; PAC, 28%; MM, 23.2%; and NRC, 16.3%). Fatal bleeding was higher in groups relying on the use of anticoagulation (W, 33.8%; PA, 9.4%; PAC, 10.8%) but the differences were not statistically significant. Our study demonstrated that the routine use of PA does not reduce the overall mortality or the proportion of deaths due to PE.

Warfarin for Venous Thromboembolism Prophylaxis After Elective Hip or Knee Arthroplasty: Exploring the Evidence, Guidelines, and Challenges Remaining

BACKGROUND:

Guidelines for the prevention of venous thromboembolism (VTE) after elective total hip or knee arthroplasty (THA/TKA) have been developed separately by the American Academy of Orthopaedic Surgeons (AAOS) and the American College of Chest Physicians (ACCP). Differences exist in approaches to preventing postoperative VTE through prophylaxis.

OBJECTIVE:

To compare trials using vitamin K antagonists (VKAs) and differences in guidelines to determine the benefits and drawbacks of warfarin for VTE prophylaxis following THA/TKA.

DATA SOURCES:

Guidelines from the AAOS published in 2009 and revised in 2011 and from the ACCP published in 2008 were compared for recommendations on the use of VKAs. A MEDLINE search from 1960 to November 2009 was conducted to identify pertinent articles on the use of warfarin or VKAs for VTE prophylaxis following THA/TKA. Search terms included warfarin, vitamin K antagonist, total hip or total knee replacement, and total hip or total knee arthroplasty.

STUDY SELECTION AND DATA EXTRACTION:

Only clinical trials in which warfarin was the primary agent for prophylaxis compared to other anticoagulants were included.

DATA SYNTHESIS:

Data on differences between guideline recommendations for the use of VKAs and the importance of a deep vein thrombosis or asymptomatic events were extracted. Thirteen comparative trials using VKAs for VTE prophylaxis and international normalized ratio (INR) targets were assessed. Overall, the incidence of bleeding tended to be lower with the use of VKAs, but thrombosis when including asymptomatic events was numerically higher when comparing INR targets. However, INR targets varied, with no comparative trials assessing the AAOS 2009 recommended INR target of 1.5-2.0. The AAOS guidelines initially recommended a longer duration of therapy and expressed stronger support for the use of aspirin for prophylaxis; however, in 2011, its guidelines were revised, with no specific recommendations as to agent, dose, or INR target goal.

CONCLUSIONS:

Warfarin is an effective agent to prevent VTE after elective THA/TKA. The most effective approach, including extended warfarin use up to 4 weeks or longer, has not been determined.

Novel oral anticoagulants for VTE prevention in orthopedic surgery: overview of phase 3 trials

Outpatient use of anticoagulants to prevent venous thromboembolism after total hip or knee arthroplasty may be hampered either by requirements for parenteral administration or high variability and frequent monitoring of anticoagulant activity. Trials of the new oral direct factor Xa inhibitors rivaroxaban and apixaban and the direct thrombin inhibitor dabigatran indicate that they can be administered in fixed doses without monitoring and that they generally have efficacy at least equivalent to enoxaparin, although with potential minor differences in the balance of efficacy vs risk for bleeding. This article reviews the results and pharmacokinetic properties that may influence their use in clinical practice.

Oral IIa inhibitors

Direct oral factor IIa inhibitors represent a new class of anticoagulants for the prevention and treatment of venous and selected arterial thomboembolisms. Dabigatran etexilate is the most studied and promising of the oral direct thrombin inhibitors. Preclinical and early-phase clinical studies show it to have a predictable and reliable pharmacokinetic and pharmacodynamic profile, whereas advanced phase 3 trials prove it to be noninferior to traditional anticoagulants in selective conditions for the prevention and treatment of venous and arterial thromboembolism. Other advantages of this drug, including a lack of interaction with cytochrome P450 enzymes or with food and drugs, rapid onset of action, good safety profile, lack of need for routine monitoring, broad therapeutic window, and fixed-dose administration, make this a competitive oral anticoagulant.

A critical appraisal of bleeding events reported in venous thromboembolism prevention trials of patients undergoing hip and knee arthroplasty

BACKGROUND

Anticoagulants are effective for the prevention of venous thromboembolism (VTE) but cause bleeding. Interpretation of the risks and benefits of new anticoagulant regimens for VTE prevention is complicated by a lack of standardized definitions and reporting of bleeding. We reviewed the reporting of bleeding in randomized controlled trials of new anticoagulants compared with standard doses of enoxaparin in hip and knee arthroplasty, and examined the possible impact of differences in the definition of major bleeding on interpretation of the trial results.

METHODS

Electronic searches identified 16 phase III trials published between 2001 and 2010 involving 41,265 patients comparing one of five new anticoagulants with a common comparator, enoxaparin.

RESULTS

Major bleeding rates in patients treated with enoxaparin ranged from 0.1% to 3.1% in hip arthroplasty trials and from 0.2% to 1.4% in knee arthroplasty trials. In studies that excluded surgical-site bleeding from the definition, major bleeding rates were about 10-fold lower than in those which included surgical-site bleeding. Within the individual trials, the choice of bleeding definition and the methods of assessment of bleeding influenced the conclusions regarding the risk of bleeding with new anticoagulant regimens relative to enoxaparin. Eight of the 16 studies demonstrated a ≥ 40% relative risk differences in major bleeding between treatment groups but the difference was statistically significant in only two of these trials.

CONCLUSION

Randomized VTE prevention trials report markedly different rates of major bleeding despite similar patient populations and doses and durations of anticoagulant prophylaxis and were underpowered to detect modest differences in patient-important bleeding events. Standardization of bleeding definitions and reporting seems desirable.

Diet as prophylaxis and treatment for venous thromboembolism?

BACKGROUND

Both prophylaxis and treatment of venous thromboembolism (VTE: deep venous thrombosis (DVT) and pulmonary emboli (PE)) with anticoagulants are associated with significant risks of major and fatal hemorrhage. Anticoagulation treatment of VTE has been the standard of care in the USA since before 1962 when the U.S. Food and Drug Administration began requiring randomized controlled clinical trials (RCTs) showing efficacy, so efficacy trials were never required for FDA approval. In clinical trials of 'high VTE risk' surgical patients before the 1980s, anticoagulant prophylaxis was clearly beneficial (fatal pulmonary emboli (FPE) without anticoagulants = 0.99%, FPE with anticoagulants = 0.31%). However, observational studies and RCTs of 'high VTE risk' surgical patients from the 1980s until 2010 show that FPE deaths without anticoagulants are about one-fourth the rate that occurs during prophylaxis with anticoagulants (FPE without anticoagulants = 0.023%, FPE while receiving anticoagulant prophylaxis = 0.10%). Additionally, an FPE rate of about 0.012% (35/28,400) in patients receiving prophylactic anticoagulants can be attributed to 'rebound hypercoagulation' in the two months after stopping anticoagulants. Alternatives to anticoagulant prophylaxis should be explored.

METHODS AND FINDINGS

The literature concerning dietary influences on VTE incidence was reviewed. Hypotheses concerning the etiology of VTE were critiqued in relationship to the rationale for dietary versus anticoagulant approaches to prophylaxis and treatment.Epidemiological evidence suggests that a diet with ample fruits and vegetables and little meat may substantially reduce the risk of VTE; vegetarian, vegan, or Mediterranean diets favorably affect serum markers of hemostasis and inflammation. The valve cusp hypoxia hypothesis of DVT/VTE etiology is consistent with the development of VTE being affected directly or indirectly by diet. However, it is less consistent with the rationale of using anticoagulants as VTE prophylaxis. For both prophylaxis and treatment of VTE, we propose RCTs comparing standard anticoagulation with low VTE risk diets, and we discuss the statistical considerations for an example of such a trial.

CONCLUSIONS

Because of (a) the risks of biochemical anticoagulation as anti-VTE prophylaxis or treatment, (b) the lack of placebo-controlled efficacy data supporting anticoagulant treatment of VTE, (c) dramatically reduced hospital-acquired FPE incidence in surgical patients without anticoagulant prophylaxis from 1980 - 2010 relative to the 1960s and 1970s, and (d) evidence that VTE incidence and outcomes may be influenced by diet, randomized controlled non-inferiority clinical trials are proposed to compare standard anticoagulant treatment with potentially low VTE risk diets. We call upon the U. S. National Institutes of Health and the U.K. National Institute for Health and Clinical Excellence to design and fund those trials.

Direct thrombin inhibitors versus vitamin K antagonists or low molecular weight heparins for prevention of venous thromboembolism following total hip or knee replacement

BACKGROUND

Patients who have undergone total hip or knee replacement (THR, TKR) have a high risk of developing venous thromboembolism (VTE) following surgery, despite appropriate anticoagulation with warfarin or low molecular weight heparin (LMWH). New anticoagulants are under investigation.

OBJECTIVES

To examine the efficacy and safety of prophylactic anticoagulation with direct thrombin inhibitors (DTIs) versus LMWH or vitamin K antagonists in the prevention of VTE in patients undergoing THR or TKR.

SEARCH STRATEGY

The Cochrane Peripheral Vascular Disease Group searched their Specialized Register (last searched 12 March 2010) and CENTRAL (last searched 2010, Issue 2).

SELECTION CRITERIA

Randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Three reviewers independently assessed methodological quality and extracted data in pre-designed tables. The reported follow-up events were included

MAIN RESULTS

We included 14 studies included involving 21,642 patients evaluated for efficacy and 27,360 for safety. No difference was observed in major VTE in DTIs compared with LMWH in both types of operations (odds ratio (OR) 0.91; 95% confidence interval (CI) 0.69 to 1.19), with high heterogeneity (I(2) 71%). No difference was observed with warfarin (OR 0.85; 95% CI 0.63 to 1.15) in TKR, with no heterogeneity (I(2) 0%).More total bleeding events were observed in the DTI group (in ximelagatran and dabigatran but not in desirudin) in patients subjected to THR (OR 1.40; 95% CI 1.06, 1.85; I(2) 41%) compared with LMWH. No difference was observed with warfarin in TKR (OR 1.76; 95% CI 0.91 to 3.38; I(2) 0%). All-cause mortality was higher in the DTI group when the reported follow-up events were included (OR 2.06; 95% CI 1.10 to 3.87).Studies that initiated anticoagulation before surgery showed less VTE events; those that began anticoagulation after surgery showed more VTE events in comparison with LMWH. Therefore, the effect of the DTIs compared with LMWH appears to be influenced by the time of initiation of coagulation more than the effect of the drug itself.The results obtained from sensitivity analysis, did not differ from the analysed results; this strengthens the value of the results.

AUTHORS' CONCLUSIONS

Direct thrombin inhibitors are as effective in the prevention of major venous thromboembolism in THR or TKR as LMWH and vitamin K antagonists. However, they show higher mortality and cause more bleeding than LMWH. No severe hepatic complications were reported in the analysed studies. Use of ximelagatran is not recommended for VTE prevention in patients who have undergone orthopedic surgery. More studies are necessary regarding dabigatran.

Review article: thromboprophylaxis after total hip replacement

The risk of secondary haematologic complications such as deep vein thrombosis or pulmonary embolism increases significantly when a transient period of hypercoagulability is induced after total hip replacement (THR). A number of drug-based anticoagulant approaches are available to modulate this risk, but the optimal length of therapy for such approaches remains unclear. The literature was reviewed for evidence-based support of the routine use of an extended course (>14 days) of thromboprophylaxis after THR. Electronic databases and real-time online literature searches were performed, using the PubMed (Medline), EMBASE, CINAHL and GoogleScholar, and the Cochrane and British Medical Journal Clinical Evidence libraries. Author-defined key word searches were performed. Only articles in the English language, for which full text could be retrieved, were reviewed. There is robust evidence to support an extended course (>14 days) of thromboprophylaxis after THR. Such recommendations have been translated into the guidelines of key professional bodies, including those of the American College of Chest Physicians. Meta-review suggests a clear benefit of such regimens and supports wider adoption, even when weighed against a small increase in adverse events.

A new era for anticoagulants

Selective inhibitors of specific coagulation factors represent a new class of antithrombotic agents, designed to overcome the limitations of traditional anticoagulants. Available clinical studies indicate that the most promising new anticoagulants are those selectively targeting factor Xa and thrombin. Typically, the standard steps for clinical evaluation of new anticoagulants are thromboprophylaxis in high risk orthopedic surgery, followed by treatment of established venous thromboembolism, nonvalvular atrial fibrillation and acute coronary syndromes. These agents - that have the potential to be more effective and easier to use than conventional drugs such as heparins and vitamin K antagonists - will greatly expand our armamentarium for the prevention and treatment of arterial and venous thromboembolism. The current knowledge on these antithrombotic agents is summarized in this review, particularly focusing on the early results of clinical trials.

State-of-the-Art Review: Assessing the Safety Profiles of New Anticoagulants for Major Orthopedic Surgery Thromboprophylaxis

Background: The safety and efficacy of new anticoagulants are often initially tested for venous thromboembolism (VTE) prevention in patients undergoing major orthopedic surgery. Concern among surgeons about the risks for bleeding may result in suboptimal use of thrombophylaxis. Objective: To evaluate the definitions used to define bleeding outcomes in studies of new anticoagulants and to examine the influence the definition has on the perceived bleeding risk of thromboprophylaxis. Methods: The MedLine database was searched for phase III studies of new anticoagulants versus the standard comparator, enoxaparin, in patients undergoing major orthopedic surgery. Results: The definitions for major bleeding outcomes varied widely both across and within clinical trial programs of new anticoagulants. Studies which did not include surgical site bleeding in their definition for major bleeding showed lower major bleeding rates in comparison to those that did include this outcome. Other factors that influenced the rate of major bleeding included the timing of prophylaxis initiation in relation to surgery and the dose of anticoagulant therapy. The wide range of definitions used for major bleeding made it difficult to compare bleeding risk among studies of new anticoagulants. Conclusions: The definitions of bleeding events that clinical trials of thromboprophylaxis use in their assessment of new anticoagulants strongly influences each drug’s perceived safety profile and may underestimate bleeding risks. Clinical studies of new anticoagulants urgently need standardization of bleeding definitions to allow intertrial comparability and to ensure consistent reporting of clinically relevant outcomes.

Lessons from ximelagatran: issues for future studies evaluating new oral direct thrombin inhibitors for venous thromboembolism prophylaxis in orthopedic surgery

Venous thromboembolism is a frequent complication of total hip and knee replacement requiring prophylaxis with anticoagulants. A direct thrombin inhibitor-ximelagatran-did not show advantages over other anticoagulants and it was withdrawn from the market; however, new drugs are being developed. We conducted a systematic review and meta-analysis to identify conditions under which ximelagatran might potentially be superior to current standards. Medline, EMBASE, the Cochrane Library, and grey literature were screened for randomized trials comparing ximelagatran with warfarin or low-molecular-weight heparin for thromboprophylaxis in total hip or knee replacement. Two reviewers independently assessed and extracted data. A meta-analysis with especial attention to statistical heterogeneity was conducted. This study suggested that the risk-benefit profile of ximelagatran-and probably other similar agents-depends on the type of surgery, the initial timing of administration, and probably the dose. These issues should be explicitly explored in future trials evaluating new direct thrombin inhibitors.

Overview of current venous thromboembolism protocols in hip reconstruction

Venous thromboembolic disease continues to be a serious complication of total-hip arthroplasty. The use of anticoagulant drugs for preventing this complication has repeatedly been proven to be useful. This article reviews the current evidence-based recommendations for anticoagulant prophylaxis after total-hip arthroplasty and provides insight into the current areas of active research and controversy.

Rivaroxaban versus enoxaparin for thromboprophylaxis after total knee arthroplasty (RECORD4): a randomised trial

BACKGROUND

Prophylaxis for venous thromboembolism is recommended for at least 10 days after total knee arthroplasty; oral regimens could enable shorter hospital stays. We aimed to test the efficacy and safety of oral rivaroxaban for the prevention of venous thromboembolism after total knee arthroplasty.

METHODS

In a randomised, double-blind, phase III study, 3148 patients undergoing knee arthroplasty received either oral rivaroxaban 10 mg once daily, beginning 6-8 h after surgery, or subcutaneous enoxaparin 30 mg every 12 h, starting 12-24 h after surgery. Patients had mandatory bilateral venography between days 11 and 15. The primary efficacy outcome was the composite of any deep-vein thrombosis, non-fatal pulmonary embolism, or death from any cause up to day 17 after surgery. Efficacy was assessed as non-inferiority of rivaroxaban compared with enoxaparin in the per-protocol population (absolute non-inferiority limit -4%); if non-inferiority was shown, we assessed whether rivaroxaban had superior efficacy in the modified intention-to-treat population. The primary safety outcome was major bleeding. This trial is registered with ClinicalTrials.gov, number NCT00362232.

FINDINGS

The primary efficacy outcome occurred in 67 (6.9%) of 965 patients given rivaroxaban and in 97 (10.1%) of 959 given enoxaparin (absolute risk reduction 3.19%, 95% CI 0.71-5.67; p=0.0118). Ten (0.7%) of 1526 patients given rivaroxaban and four (0.3%) of 1508 given enoxaparin had major bleeding (p=0.1096).

INTERPRETATION

Oral rivaroxaban 10 mg once daily for 10-14 days was significantly superior to subcutaneous enoxaparin 30 mg given every 12 h for the prevention of venous thromboembolism after total knee arthroplasty.

FUNDING

Bayer Schering Pharma AG, Johnson & Johnson Pharmaceutical Research & Development.

Cut-off values of D-dimer and soluble fibrin for prediction of deep vein thrombosis after orthopaedic surgery

Soluble fibrin (SF) and D-dimer are considered to be useful for the diagnosis of thrombosis; however, the efficacy of the diagnosis of deep vein thrombosis (DVT) after orthopaedic surgery by SF and D-dimer is still not well established. The present study was designed to evaluate the efficacy of SF and D-dimer in the diagnosis of DVT after orthopaedic surgery. The plasma concentrations of SF and D-dimer were measured in 99 patients following orthopaedic surgery. The plasma concentrations of D-dimer and SF in patients undergoing orthopaedic surgery were markedly high in comparison to healthy volunteers, and these markers were increased after surgery. The plasma concentrations of D-dimer were significantly higher in patients with DVT than in those without DVT at days 4, 7, 10 and 14, and those of SF were significantly higher in patients with DVT than in those without DVT at days 1, 4 and 14. A receiver operating characteristic (ROC) analysis of SF and D-dimer for diagnosis of DVT after surgery generated an ROC curve that showed SF to be better than D-dimer at day 1, while D-dimer was better than SF at day 4. In addition, less than 7.2 microg/ml of D-dimer or 3.6 microg/ml of SF at day 1 after surgery, or less than 7.0 microg/ml of D-dimer at day 4 excluded DVT. These findings suggest that the D-dimer and SF are useful for the diagnosis and exclusion of DVT after orthopaedic surgery.

Potent anticoagulants are associated with a higher all-cause mortality rate after hip and knee arthroplasty

Anticoagulation for thromboprophylaxis after THA and TKA has not been confirmed to diminish all-cause mortality. We determined whether the incidence of all-cause mortality and pulmonary embolism in patients undergoing total joint arthroplasty differs with currently used thromboprophylaxis protocols. We reviewed articles published from 1998 to 2007 that included 6-week or 3-month incidence of all-cause mortality and symptomatic, nonfatal pulmonary embolism. Twenty studies included reported 15,839 patients receiving low-molecular-weight heparin, ximelagatran, fondaparinux, or rivaroxaban (Group A); 7193 receiving regional anesthesia, pneumatic compression, and aspirin (Group B); and 5006 receiving warfarin (Group C). All-cause mortality was higher in Group A than in Group B (0.41% versus 0.19%) and the incidence of clinical nonfatal pulmonary embolus was higher in Group A than in Group B (0.60% versus 0.35%). The incidences of all-cause mortality and nonfatal pulmonary embolism in Group C were similar to those in Group A (0.4 and 0.52, respectively). Clinical pulmonary embolus occurs despite the use of anticoagulants. Group A anticoagulants were associated with the highest all-cause mortality of the three modalities studied.

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.

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.

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.

The 2007 ABJS Nicolas Andry Award: three decades of clinical, basic, and applied research on thromboembolic disease after THA: rationale and clinical results of a multimodal prophylaxis protocol

Total hip arthroplasty is an operation with a high risk for venous thromboembolism. Three decades of research conducted at the Hospital for Special Surgery identified the exact timing of the thrombogenic stimulus during surgery, defined the role of magnetic resonance venography, and established the role of certain genetic and acquired predispositions. Based on these studies, we implemented a multimodal prophylaxis consisting of a series of safe preventive measures applied before, during, and immediately after surgery to reduce the risk of venous thromboembolism. If these safe preventive measures are strictly observed, postoperative pharmacologic prophylaxis does not need to be aggressive in the patient without predisposing factors who mobilizes promptly, thus diminishing the risk of bleeding associated with the use of anticoagulants and the overall cost of care. Our clinical experience with more than 5000 total hip arthroplasties performed during the last decade and closely followed prospectively for a minimum of 3 months clearly shows this multimodal prophylaxis is safe and effective resulting in a very low prevalence of thromboembolism.

[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.

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.

Catheter-Related Central Venous Thrombosis: The Development of a Nationwide Consensus Paper in Italy

Catheter-related central venous thrombosis is a serious complication in patients who need long-term venous access. Though scientific data and clinical experience are steadily increasing, many uncertainties still exist about several aspects of this complication, including etiology, pathogenesis, diagnosis, management, and prevention of this complication. The GAVeCeLT (the Italian Study Group for Long Term Central Venous Access) promoted a nationwide consensus, and 12 experts reviewed systematically all the available literature. A preliminary document was presented and discussed during a specific Consensus Meeting, in front of a panel of more than 80 experts (representing different health professions and disciplines). This led to a prefinal document, which was presented to more than 800 health professionals. After peer review by an external board of experts, the final document was prepared. In this article, methodology and results of the consensus are presented.

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.

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.

The status of new anticoagulants

Currently available anticoagulants include heparin, low-molecular weight heparin, fondaparinux and warfarin. Despite advances with low-molecular weight heparin and fondaparinux, the currently available agents have limitations that have provided the impetus for the development of new drugs for prevention and treatment of both venous and arterial thromboembolism. Novel anticoagulants targeting specific steps in coagulation are in various stages of development. This paper reviews the pharmacology of these new agents and describes the results of clinical trials with new anticoagulants in more advanced stages of clinical testing.

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.

Venous thromboembolism is rare with a multimodal prophylaxis protocol after total hip arthroplasty

We evaluated the safety and efficacy of a multimodal approach for prophylaxis of thromboembolism after total hip arthroplasty, which includes preoperative discontinuation of procoagulant medication; autologous blood donation; hypotensive epidural anesthesia; intravenous administration of heparin during surgery and before femoral preparation; aspiration of intramedullary contents; pneumatic compression; knee-high elastic stockings; and early mobilization and chemoprophylaxis for 4 to 6 weeks (aspirin 83%; warfarin 17%). One thousand nine hundred forty-seven consecutive, nonselected patients (2032 total hip arthroplasties) who received this multimodal prophylaxis were observed prospectively for 3 months. The incidence of asymptomatic deep vein thrombosis assessed by ultrasound in the first 171 patients was 6.4%. The incidence of clinical deep vein thrombosis in the subsequent 1776 patients was 2.5%. Symptomatic pulmonary embolism occurred in 0.6% (12 of 1947; nine in patients receiving aspirin and three in patients receiving Coumadin), none of them fatal. One patient died of a myocardial infarct. This multimodal approach is safe and efficacious and compares favorably with those reported in the literature and with our historic controls. If these preventive measures are strictly observed during the perioperative period, postoperative chemoprophylaxis does not need to be aggressive in the patient without predisposing factors. Our low rate of deep vein thrombosis and pulmonary embolism do not support routine anticoagulation prophylaxis with drugs that increase risk of bleeding.

LEVEL OF EVIDENCE

Therapeutic study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

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.

Update in the prevention and treatment of deep vein thrombosis and pulmonary embolism

PURPOSE OF REVIEW

Thromboembolic events have a major impact on outcome of surgical and medical patients. This review is focused on standards and recent advances in antithrombotic strategies for prevention and therapy of venous thromboembolism and pulmonary embolism.

RECENT FINDINGS

Alert programs improve prophylactic strategies to prevent venous thromboembolism. Evidenced-based guidelines are available on antithrombotic and thrombolytic therapy outweighing the benefits, risks, burdens and costs. Selective factor Xa and direct thrombin inhibitors are at least as effective as low-molecular-weight heparin in prevention of venous thromboembolism and treatment of pulmonary embolism, but have fewer side effects and will not need routine monitoring. In high-risk orthopaedic patients but not in general surgery patients fondaparinux is superior to low-molecular-weight heparin in the prevention of thromboembolic disease. Ximelagatran, the first oral direct thrombin inhibitor, is as effective and well tolerated as warfarin. Long-term treatment is uncertain, however, because of elevation in alanine transaminase levels. In high-risk patients with contraindication for anticoagulation, retrievable vena cava filters may be an option to prevent pulmonary embolism. Permanent cava filters do not improve long-term survival and are associated with relevant side effects. Thrombolytics should be reserved for deep venous thrombosis complicated by limb gangrene and for life threatening pulmonary embolism.

SUMMARY

There is currently sufficient information based on guidelines available on preventive and therapeutic strategies for venous thromboembolism and pulmonary embolism. Antithrombotics are the therapeutic backbone. In high-risk orthopedic surgery and venous thromboembolism the new antithrombotics fondaparinux, idraparinux and ximelagatran are superior to standard treatment. Temporary caval filters may be a therapeutic option in high-risk patients with contraindication for antithrombotics.

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.