A new oral direct thrombin inhibitor, dabigatran etexilate, compared with enoxaparin for prevention of thromboembolic events following total hip or knee replacement: the BISTRO II randomized trial

Venous thrombosis in children: an emerging issue

More and more cases of venous thrombosis are diagnosed in children thanks to newer imaging modalities. Central venous catheters have become commonplace in the care of critically ill children and have contributed to the increased rate of thrombotic events. Lastly, children who develop life-threatening or chronic medical conditions are surviving longer because of advanced medical therapies; these intensive therapies can be complicated by events such as thrombosis. Over the last 10 years, specific guidelines for treating thrombosis in children have become available. Nevertheless, in many situations anticoagulant treatment is specially tailored to each individual patient's needs. Some new antithrombotic drugs which have undergone clinical testing in adults might be beneficial to paediatric patients with thromboembolic disorders; unfortunately, clinical data and reports on the use of these drugs in children, when available, are extremely limited. The aim of this review is to provide physicians with enough background information to be able to manage thrombosis in children. First, by helping them detect a thrombotic event in a child. Upon confirmation of the diagnosis, the physician will request the appropriate tests and will choose the best treatment on the basis of the guidelines and recommendations. Moreover, the paediatrician will have the information he or she needs to identify which children are at highest risk of acute thrombotic events and relevant long-term sequelae and, therefore, to decide on the appropriate prophylactic or pharmacologic strategy. Lastly, we would like to provide the paediatrician with information on future drugs with regard to the treatment and prophylaxis of thrombosis.

Pharmacological basis and clinical evidence of dabigatran therapy

Dabigatran is an emerging oral anticoagulant which is a direct inhibitor of thrombin activity. It has been approved in the European Union and the United States of America for the prevention of thrombosis after major orthopedic surgery. It has also been approved by the American Food and Drug Administration and the European Medicines Agency for the prevention of stroke in chronic atrial fibrillation. Dabigatran provides a stable anticoagulation effect without any need to perform periodical laboratory controls. Of note, there is a growing amount of clinical evidence which shows its safety and efficacy. For these reasons, dabigatran may suppose a revolution in oral anticoagulation. However, two important limitations remain. First, it is contraindicated in patients with end-stage renal disease. Second, there is no evidence of the prevention of thrombosis in mechanical heart valves.

New anticoagulants: moving on from scientific results to clinical implementation

Vitamin K antagonists (VKA) are the only registered oral anticoagulants for the treatment of venous thromboembolism (VTE). VKA have an unpredictable and highly variable effect on coagulation, with a high risk of under- and over-treatment. Novel anticoagulants, such as dabigatran and rivaroxaban, could be a very welcome replacement for VKA, as they show a predictable anticoagulant effect. Results of several phase II and III studies have shown the efficacy and safety of dabigatran and rivaroxaban in the prophylaxis and treatment of VTE, and for the prevention of stroke in atrial fibrillation. It remains to be shown whether these new anticoagulants have the same safety profile in daily clinical practice, where more vulnerable patients will be treated. Lack of information on the proper monitoring method or antidote in case of bleeding may also hinder the translation from science to clinical practice.

[New antithrombotic drugs for the treatment of venous thromboembolism]

Numerous newer anticoagulants are under advanced clinical development for the treatment of venous thromboembolism. These new drugs specifically inhibit activated factors II or X, with predictable effects and no need for dose modification and laboratory monitoring. The main direct activated factor X (FXa) inhibitors are rivaroxaban, apixaban and edoxaban. They are taken orally once or twice per day. Dabigatran is the main inhibitor of activated factor II (IIa) and is administered orally once daily. Dabigatran and rivaroxaban are already licensed for the prevention of thromboembolic events following major orthopedic surgery such as total hip and knee replacement. They will probably soon be authorized for the treatment of venous thromboembolism, if they both confirm their efficacy and safety, and can demonstrate their cost-effectiveness. However, only rivaroxaban has been tested as a stand-alone treatment, whereas dabigatran was compared to vitamin K antagonism after a standard treatment regimen based on heparin or its derivates.

Thromboprophylaxis in patients older than 75 years or with moderate renal impairment undergoing knee or hip replacement surgery [corrected]

PURPOSE

Prospective, double-blind studies in orthopaedic patients have been conducted using the direct thrombin inhibitor dabigatran etexilate (hereafter referred to as dabigatran), with two doses investigated and approved for adults (220 mg and 150 mg once daily) to prevent venous thromboembolism (VTE). The European Medicines Agency decided that in major joint orthopaedic surgery, the lower dose should be used in elderly patients (aged over 75 years) and those with reduced renal function (creatinine clearance between 30 and 50 ml/min). Our objective was to understand the efficacy and bleeding data for the lower dose in this subpopulation.

METHODS

We extracted and analysed data from the elderly or from moderately renally impaired patients (n 632 of = 5,539) from the orthopaedic clinical development programme of dabigatran.

RESULTS

Dabigatran 150 mg once daily was as effective as the standard European enoxaparin regimen, with numerically fewer major bleeding events. Rates of major VTE were 4.3% vs 6.4% of patients, respectively. Major bleeding events occurred in four (1.3%) vs 11 (3.3%), which shows a trend towards lower bleeding with dabigatran 150 mg [odds ratio (OR) 0.40; 95% confidence interval (CI) 0.13-1.25; p = 0.110]. Mean volume of blood loss was 395 vs 417 ml, and transfused units were 2.4 vs 2.5, respectively. Other safety parameters, including the incidence of wound infections and complications, were similar for 150 mg once daily dabigatran and enoxaparin.

CONCLUSION

For patients at higher risk of bleeding, dabigatran 150 mg once daily is as effective as enoxaparin following major orthopaedic surgery and is associated with a favourable bleeding rate.

Approved Uses of Dabigatran Etexilate as an Anticoagulant

Objective:

To review, analyze, and critique dabigatran etexilate's approved uses as an anticoagulant.

Data Sources:

Literature searches were performed via MEDLINE, International Pharmaceutical Abstracts, and Google Scholar through February 2011, using the term dabigatran. Additional data were obtained from tertiary sources and prescribing information.

Study Selection and Data Extraction:

All published Phase 3 anticoagulation trials investigating dabigatran for currently approved indications were selected. Information from other anticoagulation trials investigating dabigatran was used for critiquing Phase 3 studies.

Data Synthesis:

Dabigatran etexilate has been evaluated in multiple clinical trials as an alternative to enoxaparin for prevention of venous thromboembolism in total hip and knee replacement surgeries. It has also been evaluated as an alternative to warfarin in stroke and systemic embolism prevention in patients with atrial fibrillation. Results have generally been positive, with few exceptions. The standard adult dose of dabigatran 150 mg twice daily, approved for use in the US for stroke prevention in nonvalvular atrial fibrillation, was found to be superior to warfarin in regard to occurrence rates of stroke or systemic embolism and hemorrhagic stroke. The occurrence rates of intracranial bleeding, life-threatening bleeding, and major or minor bleeding were lower with dabigatran 150 mg twice daily than with warfarin; however, the occurrence of gastrointestinal bleeding was significantly higher.

Conclusions:

With its numerous benefits, and despite its drawbacks, dabigatran remains a promising option for oral anticoagulation therapy.

Direct thrombin inhibitors

Heparins and vitamin K antagonists have been the primary agents used for anticoagulation in certain cardiovascular and thromboembolic diseases for over 50 years. However, they can be difficult to administer and are fraught with limitations. In response to the need for new anticoagulants, direct thrombin inhibitors (DTIs) have been developed and investigated for their utility in prophylaxis and treatment of venous thromboembolism (VTE), heparin-induced thrombocytopenia (HIT), acute coronary syndromes (ACS), secondary prevention of coronary events after ACS, and nonvalvular atrial fibrillation. Currently, four parenteral direct inhibitors of thrombin activity are FDA-approved in North America: lepirudin, desirudin, bivalirudin and argatroban. Of the new oral DTIs, dabigatran etexilate is the most studied and promising of these agents. This review discusses the clinical indications and efficacy of these direct thrombin inhibitors as well as future directions in anticoagulant therapy.

Old versus new oral anticoagulants: focus on pharmacology

Since the discovery of heparin nearly a century ago, there have been large gaps in the development of anticoagulants. The discovery of warfarin was the first step toward using oral anticoagulants, but warfarin use has been associated with its own challenges from the perspectives of the prescribing physician and the patient. Warfarin, along with other coumarins, has a narrow therapeutic index, requires frequent monitoring, exhibits interindividual response variations, and is associated with several adverse effects. Frequent drug and food interactions contribute to potential safety and efficacy compromise. The indications for use of oral anticoagulants have increased, as these drugs are used not only for thrombosis management but also for cardiovascular indications, producing more challenges for oral anticoagulant use. Factor Xa and thrombin targeting has provided a rational approach to develop new oral anticoagulants with improvements over warfarin. In this review, the pharmacology of warfarin and the pharmacology of the newly developed oral anti-Xa and antithrombin agents are discussed.

New anticoagulants: pharmacology and clinical studies

The marketing of new anticoagulant drugs has led us to review the development of rivaroxaban and apixaban (oral anti-Xa drugs) and dabigatran (an oral thrombin inhibitor). The results are different in terms of efficacy and tolerance. Each molecule has its own field of application but it is not at all certain that each will find its place. Though the results are favourable for these orally active drugs in the orthopaedic setting, it is clear that only cardiological applications will give a final green light for these products. The future will be fascinating in this regard.

Management of anticoagulation therapy in the perioperative patient

With the increasing use of oral anticoagulation therapy the appropriate management of perioperative anticoagulation is of surgical importance. There is a delicate balance between the risk of a perioperative thromboembolic event and the risk of operative bleeding from anticoagulation. Whilst there are a range of options available to the clinician, there appears to be no precise agreement about how to best manage this problem.

Dabigatran etexilate: the first oral anticoagulant available in the United States since warfarin

For more than 5 decades, warfarin has been the mainstay of therapy when oral anticoagulation is required. It has been shown to be effective in the prevention as well as treatment of various thromboembolic disorders. However, drawbacks of warfarin, such as time-consuming requirements for frequent international normalized ratio monitoring, as well as drug and food interactions, have encouraged the development of alternative oral agents. One such agent, dabigatran, has risen up to the challenge. Due to its predictable anticoagulation response, dabigatran does not require routine anticoagulation monitoring. Another advantage dabigatran has over warfarin is its more favorable drug and food interaction profiles. Dabigatran was shown to be noninferior to warfarin in studies evaluating the prevention of stroke and systemic embolism in patients with atrial fibrillation, thus leading to the US Food and Drug Administration approval for this indication. Dabigatran has also demonstrated efficacy in the prevention of venous thromboembolism in patients undergoing total hip or knee replacement surgery as well as the prevention of recurrent venous thromboembolism, although these are not current Food and Drug Administration-approved indications. The safety profile appears to be similar to warfarin with regards to overall bleeding risk, though the risk for gastrointestinal bleeds was higher in patients on dabigatran 150 mg twice daily. Disadvantages of dabigatran may include a higher frequency of dyspepsia compared with warfarin, lack of dosing information in severe renal impairment, possible missed opportunities for periodic health examinations and interventions due to elimination of regular physician's visit for international normalized ratio monitoring, and drug costs. This article provides an overview of the clinical studies, pharmacokinetic profile, adverse effects, drug interactions as well as advantages and disadvantages associated with dabigatran.

[Incidence and distribution of venous thrombosis of the lower limbs diagnosed by duplex ultrasonography after total hip or total knee arthroplasty, and hip fracture surgery. Results from 5981 exams and 2123 cases of venous thrombosis over 10 years]

AIM

To determine the incidence and distribution of lower limb venous thrombosis diagnosed by duplex ultrasonography, including calf exploration, after total hip or knee replacement or hip fracture, and to compare them with the venographic results reported by recent randomized control trials testing new antithrombotic drugs.

PATIENTS AND METHODS

From January 2001 to December 2009, 30,510 standardized report forms incremented a database from which files corresponding to major orthopaedic surgery were selected: 1652 after total hip replacement (THR), 1440 after total knee replacement (TKR) and 2889 after hip fracture (HF). Base-line characteristics, incidence and anatomic distribution of venous thrombosis were analysed in the three populations.

RESULTS

Systematic screening was applied for 95.1% of the exams (n=5689). Incidence of total and proximal venous thrombosis was, respectively, 27.8% (n=460) and 2.8% (n=46) for THR, 32.5% (n=939) and 4.4% (n=126) for HF, and 50.3% (n=724) and 3.8% (n=55) for TKR. Venous thrombosis was distal in 89.3% (n=1896). More than half (n=1014) of distal venous thromboses were strictly muscular soleal locations. Ilio-caval thrombosis incidence was 0.18% (n=11), and superficial venous thrombosis incidence was 1.5% (n=89).

CONCLUSION

This study shows that incidence and distribution of venous thromboses diagnosed with a complete and standardized duplex ultrasonographic screening are very close to the rates published with venographic screening in recent trials.

Efficacy and safety of novel anticoagulants compared with established agents

Dabigatran, rivaroxaban, and apixaban are novel oral anticoagulants that offer major advantages over existing agents. The onset of the anticoagulant effect of these agents is rapid. Each agent has a predictable anticoagulant response that eliminates the need for monitoring. Clinical trials have been completed with all three agents in the prevention and treatment of the three leading causes of cardiovascular death: myocardial infarction, stroke, and venous thromboembolism (VTE). Novel agents have shown reduced or similar rates of thrombosis, major bleeding, and adverse events when weighed against either low molecular weight heparin or warfarin. Additional trials are underway and more agents are in development. As a result, novel anticoagulants may impact physician prescribing practices and warrant consideration in patients requiring thrombosis management.

Prophylaxis for venous thromboembolism: guidelines translated for the clinician

Venous thromboembolism is a major cause of morbidity and mortality worldwide and most often affects hospitalized postoperative surgical and medical patients. Venous thromboembolism prophylaxis undoubtedly improves the care of these patients, as demonstrated by the current literature and guidelines. Failure to prescribe prophylaxis when indicated, however, remains a vital health care concern. The American College of Chest Physicians (ACCP) published their most recent guidelines regarding venous thromboembolism prophylaxis in 2008. In this review, we aim to summarize the most recent ACCP prophylaxis guidelines with practical application and interpretation for the practicing physician. Here we present the most practical information from these guidelines and summarize essential recommendations in key tables. We will briefly review the grading system used in the guidelines for the level of evidence and the strength of the recommendation. We will then discuss the recommendations for prophylaxis in the various patient populations described in these guidelines including general and orthopedic surgery, gynecologic surgery, urologic surgery, thoracic surgery, neurosurgery, trauma, medical conditions, cancer patients, and critical care. In addition, we will discuss recent clinical trials regarding novel anticoagulants for venous thromboembolism prophylaxis and share some conclusions.

[Patient pathways in thrombosis prophylaxis after hip and knee replacement surgery : results of a survey]

A key element of patient care after hip and knee replacement is medication-based thrombosis prophylaxis. Due to decreasing lengths of acute hospital stays the question arises to what extent outpatients are taking responsibility thrombosis prophylaxis (patient pathway analysis).To analyze patient pathways a telephone survey of 668 patients was conducted. On average patients were interviewed 38 days following surgery with a focus on low molecular weight heparins. The analysis showed that nearly 90% of patients need to carry out thrombosis prophylaxis in an outpatient or home environment for at least 1 day and for 47.2% of patients a linking period between acute and rehabilitation stay is relevant. The obviously existing quantitative importance of outpatient thrombosis prophylaxis is also reflected by its duration and 45.7% of interviewed patients needed at least 5 days of outpatient prophylaxis.Outpatient thrombosis prophylaxis clearly makes high demands on the patients, in particular when combined with the task of administering complex forms of injections. Those involved in inpatient and outpatient provision of care should not assume that all patients carry out the necessary prophylaxis at the required level of reliability. On the contrary initial evidence shows that the non-adherence of patients during ambulatory thrombosis prophylaxis presents a genuine challenge to care providers.

Pharmacoeconomics of dabigatran etexilate for prevention of thromboembolism after joint replacement surgery

Dabigatran etexilate (DE) is a novel oral anticoagulant indicated for the prevention of venous thromboembolism in patients undergoing total hip or total knee replacement surgery. The majority of these patients receive some kind of thromboprophylaxis, most commonly low-molecular-weight heparin (LMWH). However, the subcutaneous route of LMWH administration may act as a barrier to the continuation of effective anticoagulant prophylaxis after discharge from hospital. The oral route of DE administration may allow more patients to receive extended thromboprophylaxis and may reduce costs, such as those associated with nurse time for LMWH administrations, platelet monitoring, needlestick injuries and sharps disposal. This article presents an overview of the clinical evidence for DE and a systematic review of the economic evaluations of the drug.

Dabigatran

Each month, subscribers to The Formulary Monograph Service receive 5 to 6 well-documented monographs on drugs that are newly released or are in late phase 3 trials. The monographs are targeted to Pharmacy & Therapeutics Committees. Subscribers also receive monthly 1-page summary monographs on agents that are useful for agendas and pharmacy/nursing in-services. A comprehensive target drug utilization evaluation/medication use evaluation (DUE/MUE) is also provided each month. With a subscription, the monographs are sent in print and are also available on-line. Monographs can be customized to meet the needs of a facility. Subscribers to The Formulary Monograph Service also receive access to a pharmacy bulletin board, The Formulary Information Exchange (The F.I.X.). All topics pertinent to clinical and hospital pharmacy are discussed on The F.I.X. Through the cooperation of The Formulary, Hospital Pharmacy publishes selected reviews in this column. For more information about The Formulary Monograph Service or The F.I.X., call The Formulary at 800-322-4349. The March 2011 monograph topics are on fentanyl sublingual tablet, brentuximab vedotin, rilpivirine hydrochloride, denufosol, abiraterone acetate. The DUE/MUE is on dabigatran etexilate mesylate.

Dabigatran etexilate: a possible replacement for heparinoids and vitamin K antagonists?

Dabigatran etexilate is the first oral anticoagulant to be approved in the United States in decades. It works directly by inhibiting clot-bound and free factor IIa (ie, thrombin) and indirectly by inhibiting platelet aggregation induced by thrombin. It is approved in the United States for stroke prophylaxis in nonvalvular atrial fibrillation. There is evidence to suggest that it is also effective for the treatment of acute venous thromboembolism and venous thromboembolism prophylaxis after knee and hip replacement surgery. Dabigatran etexilate therapy does not require laboratory monitoring, an advantage over warfarin. Unlike the earlier direct thrombin inhibitor, ximelagatran, it has demonstrated no potential for serious hepatotoxicity. It is also subject to a much lower degree of interpatient variability in dose response, has no diet-drug interactions, and has fewer clinically significant drug-drug interactions compared with warfarin. Dabigatran etexilate appears to be a valuable addition to our anticoagulant armamentarium.

Novel anticoagulants: a discussion of clinical use in the treatment and prevention of venous thromboembolism

Traditional therapeutic oral anticoagulation strategies often require invasive dosing or monitoring. Vitamin K antagonists (VKAs) have a large number of interactions, delayed onset requires frequent dose monitoring, and they have a small margin between therapeutic dose and bleeding complications. Novel oral anticoagulants, such as dabigatran, rivaroxaban and apixaban, are being developed to prevent those VKAs drawbacks. Besides oral bioavailability, those compounds are designed to require minimal to no monitoring and have a favourable safety profile. This review reports efficacy and safety data of these compounds throughout clinical development, as well as new approaches for oral pharmacological management of venous thromboembolism.

Oral dabigatran versus enoxaparin for thromboprophylaxis after primary total hip arthroplasty (RE-NOVATE II*). A randomised, double-blind, non-inferiority trial

This trial compared the efficacy and safety of oral dabigatran, a direct thrombin inhibitor, versus subcutaneous enoxaparin for extended thromboprophylaxis in patients undergoing total hip arthroplasty. A total of 2,055 patients were randomised to 28-35 days treatment with oral dabigatran, 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. The primary efficacy outcome was a composite of total venous thromboembolism [VTE] (venographic or symptomatic) and death from all-causes. The main secondary composite outcome was major VTE (proximal deep-vein thrombosis or non-fatal pulmonary embolism) plus VTE-related death. The main safety outcome was major bleeding. In total, 2,013 were treated, of whom 1,577 operated patients were included in the primary efficacy analysis. The primary efficacy outcome occurred in 7.7% of the dabigatran group versus 8.8% of the enoxaparin group, risk difference (RD) -1.1% (95%CI -3.8 to 1.6%); p<0.0001 for the pre-specified non-inferiority margin. Major VTE plus VTE-related death occurred in 2.2% of the dabigatran group versus 4.2% of the enoxaparin group, RD -1.9% (-3.6% to -0.2%); p=0.03. Major bleeding occurred in 1.4% of the dabigatran group and 0.9% of the enoxaparin group (p=0.40). The incidence of adverse events, including liver enzyme elevations and cardiac events, during treatment was similar between the groups. Extended prophylaxis with oral dabigatran 220 mg once-daily was as effective as subcutaneous enoxaparin 40 mg once-daily in reducing the risk of VTE after total hip arthroplasty, and superior to enoxaparin for reducing the risk of major VTE. The risk of bleeding and safety profiles were similar.

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.

Novel anticoagulant therapy: principle and practice

Currently, there are several lines of evidence supporting the interplay between coagulation and inflammation in the propagation of various disease processes, including venous thromboembolism (VTE) and inflammatory diseases. Major advances in the development of oral anticoagulants have resulted in considerable progress toward the goal of safe and effective oral anticoagulants that do not require frequent monitoring or dose adjustment and have minimal food/drug interactions. Indirect inhibitors such as low-molecular-weight heparin (LMWH) and the pentasaccharide fondaparinux represent improvements over traditional drugs such as unfractionated heparin for acute treatment of VTE, constituting a more targeted anticoagulant approach with predictable pharmacokinetic profiles and no requirement for monitoring. Vitamin K antagonist, with its inherent limitations in terms of multiple food and drug interactions and frequent need for monitoring, remains the only oral anticoagulant approved for long-term secondary thromboprophylaxis in VTE. The oral-direct thrombin inhibitor ximelagatran was withdrawn from the world market due to safety concerns. Newer anticoagulant drugs such as parenteral pentasaccharides (idraparinux, SSR126517E), novel oral-direct thrombin inhibitors (dabigatran), oral-direct factor Xa inhibitors (rivaroxaban, apixaban, YM-150, DU-176b), and tissue factor/factor VIIa complex inhibitors have been "tailor-made" to target specific procoagulant complexes and have the potential to greatly expand oral antithrombotic targets for both acute and long-term treatment of VTE, acute coronary syndromes, and for the prevention of stroke in atrial fibrillation patients.

Dabigatran: An Oral Novel Potent Reversible Nonpeptide Inhibitor of Thrombin

Dabigatran is a highly selective, reversible, and potent thrombin inhibitor and is orally available as the prodrug, dabigatran etexilate. It has shown antithrombotic efficacy in animal models of thrombosis, with a rapid onset of action and predictable pharmacodynamic response. Peak plasma concentrations of dabigatran occur 1 to 2 hours after ingestion of the prodrug. The terminal half-life of dabigatran is 12 to 14 hours in elderly volunteers. Dabigatran is not metabolized by cytochrome P450 isoenzymes and does not interact with food. Dabigatran has a low potential for drug-drug interactions and is predominantly renally excreted. Dabigatran etexilate as chronic therapy effectively prevents the recurrence of venous thromboembolism and cardioembolic stroke. For the first time, it has been demonstrated clinically that there may be an effective and safe alternative to warfarin.

Dabigatran versus enoxaparin for prevention of venous thromboembolism after hip or knee arthroplasty: a pooled analysis of three trials

BACKGROUND

Three randomized, double-blind trials compared dabigatran, an oral direct thrombin inhibitor, with enoxaparin for the primary prevention of venous thromboembolism (VTE) in patients undergoing elective total hip and knee arthroplasty.

OBJECTIVES AND METHODS

We conducted a pre-specified pooled analysis of these trials. 8,210 patients were randomized, of whom 8,135 were treated (evaluable for safety) with dabigatran 220 mg or 150 mg once-daily, or subcutaneous enoxaparin (40 mg once-daily or 30 mg twice-daily). Efficacy analyses were based on the modified intention-to-treat population of 6,200 patients with an evaluable outcome. The common risk difference (RD) of treatment effect between each dabigatran dose and enoxaparin was estimated using fixed-effects models, and statistical heterogeneity was estimated using the I2 statistic.

RESULTS

The composite outcome of major VTE (proximal deep vein thrombosis and/or pulmonary embolism) and VTE-related mortality occurred in 3.3% of the enoxaparin group versus 3.0% of the dabigatran 220 mg group (RD vs. enoxaparin -0.2%, 95% CI -1.3% to 0.9%, I2=37%) and 3.8% of the 150 mg group (RD vs. enoxaparin 0.5%, -0.6% to 1.6%, I2=0%). Major bleeding occurred in 1.4% of the enoxaparin group versus 1.4% of the dabigatran 220 mg group (RD vs. enoxaparin -0.2%, -0.8% to 0.5%, I2=40%) and 1.1% of the 150 mg group (RD vs. enoxaparin -0.4%, -1.0% to 0.2%, I2=0%).

CONCLUSIONS

Oral dabigatran was as effective as subcutaneous enoxaparin in reducing the risk of major VTE and VTE-related mortality after hip or knee arthroplasty and has a similar bleeding profile.

Nonadherence in outpatient thrombosis prophylaxis with low molecular weight heparins after major orthopaedic surgery

BACKGROUND

According to some current guidelines, extended thromboprophylaxis after hip and knee arthroplasties is recommended. Outpatient prophylaxis with low molecular weight heparins (LMWH) is an important part of this prophylaxis, although the rates of adherence to these regimens is not known.

QUESTIONS/PURPOSES

We determined (1) the degree of nonadherence (NA) of patients with LMWH outpatient prophylaxis, and (2) whether specific independent factors explain NA.

METHODS

NA was determined by syringe count and by indirect and direct questions to patients. We defined six different NA indicators. To identify factors explaining LMWH NA, we used three different logistic regression models.

RESULTS

NA rates ranged between 13% and 21% depending on the indicator used for measurement. Patients who were nonadherent missed between 38% and 53% of their outpatient LMWH injections. If patients attended an outpatient rehabilitation program, the probability for their NA increased substantially. Moreover, the NA probability increased with each additional day between acute hospitalization and start of rehabilitation (linking days). NA was lower for patients who feared thrombosis or who believed antithrombotic drugs to be the most important measure in thromboprophylaxis.

LEVEL OF EVIDENCE

Level II, prognostic study. See the Guidelines for Authors for a complete description of levels of evidence.

Dabigatran acylglucuronide, the major human metabolite of dabigatran: in vitro formation, stability, and pharmacological activity

Glucuronidation of the carboxylate moiety is the major human metabolic pathway of dabigatran (beta-alanine, N-[[2-[[[4-(aminoiminomethyl)phenyl]amino]methyl]-1-methyl-1H-benzimidazol-5-yl]carbonyl]-N-2-pyridinyl). It results in the formation of the 1-O-acylglucuronide. Four isomeric acylglucuronides of dabigatran were isolated and purified from urine of dosed rhesus monkeys. NMR analysis confirmed the structures of the four metabolites as the 1-O-acylglucuronide (beta anomer) and the 2-O-, 3-O-, and 4-O-acylglucuronides (alpha and beta anomers). Experiments with the purified 1-O-acylglucuronide and its isomeric rearrangement products revealed equipotent prolongation of the activated partial thromboplastin time compared with dabigatran. The 1-O-acylglucuronide, in addition to minor hydrolysis to the aglycon, underwent nonenzymatic acyl migration in aqueous solution, resulting in the formation of the 2-O-, 3-O-, and 4-O-acylglucuronides with an apparent half-life of 1 h (37 degrees C, pH 7.4). The glucuronidation of dabigatran was catalyzed by human hepatic and intestinal microsomes with K(m) values in the range of 180 to 255 and 411 to 759 microM, respectively. Three UDP-glucuronosyltransferases (UGTs), namely, UGT1A9, UGT2B7, and UGT2B15, exhibited glucuronidation of dabigatran. Based on a comparison of the in vitro intrinsic clearances, UGT2B15 was considered the major contributor to the glucuronidation of dabigatran. The major contribution of UGT2B15 and the minor contribution of at least two more UGT enzymes together with the lack of potent inhibition of dabigatran glucuronidation by several potential UGT inhibitors indicate a low risk of interaction by co-medications on dabigatran glucuronidation in the clinic.

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.

New oral anticoagulants for thromboprophylaxis after elective total hip and knee arthroplasty

Anticoagulant drugs reduce the risk of venous thromboembolic events after total hip and knee arthroplasty. However, the use of current drugs, such as low molecular weight heparins, is hampered by their subcutaneous route of administration. The use of vitamin K antagonists is hampered by the requirement for routine coagulation monitoring and dose titration to provide effective anticoagulation without an increased risk of bleeding and numerous food and drug interactions. Clearly, there is a need for new oral, fixed-dose anticoagulant drugs that do not require coagulation monitoring, while demonstrating similar or better efficacy and safety profiles when compared with current agents.

Venous thromboembolism following prolonged cast immobilisation for injury to the tendo Achillis

We report an audit of 208 patients with a mean age of 39 years (16 to 65) attending the Orthopaedic Assessment Unit at the Wellington Hospital between January 2006 and December 2007 with an injury of the tendo Achillis requiring immobilisation in a cast. Information on assessment of venous thromboembolism (VTE) risk, prophylactic measures and VTE events for all patients was obtained from the medical records. A VTE risk factor was documented in the records of three (1%) patients. One of the 208 patients received aspirin prophylaxis; none received low molecular weight heparin. In all, 13 patients (6.3%, 95% confidence interval 3.4 to 10.5) developed symptomatic VTE during immobilisation in a cast, including six with a distal deep-vein thrombosis (DVT), four with a proximal DVT, and three with a confirmed pulmonary embolus. This incidence of symptomatic VTE is similar to that reported following elective hip replacement. We propose that consideration is given to VTE prophylaxis during prolonged immobilisation of the lower limbs in a cast, to ensure that the same level of protection is provided as for patients undergoing elective hip replacement.

Drug and dietary interactions of the new and emerging oral anticoagulants

Oral warfarin is associated with extensive food and drug interactions, and there is a need to consider such interactions with the new oral anticoagulants (OACs) dabigatran etexilate, rivaroxaban and apixaban. A literature survey was conducted using PubMed, EMBASE and recent abstracts from thrombosis meetings to identify publications related to food, drug and dietary supplement interaction studies with dabigatran etexilate, rivaroxaban and apixaban. Clinical experience regarding food interactions is currently limited. Regarding drug-drug interactions, dabigatran requires caution when used in combination with strong inhibitors or inducers of P-glycoprotein, such as amiodarone or rifampicin. Rivaroxaban (and possibly apixaban) is contraindicated in combination with drugs that strongly inhibit both cytochrome P450 3A4 and P-glycoprotein, such as azole antimycotics, and caution is required when used in combination with strong inhibitors of only one of these pathways. Important drug interactions of the new OACs that can lead to adverse clinical reactions may also occur with non-steroidal anti-inflammatory drugs and antiplatelet drugs, such as aspirin and clopidogrel. Over-the-counter (OTC) medications and food supplements (e.g. St. John's Wort) may also interact with the new OACs. Given the common long-term use of drugs for some chronic disorders, the frequent use of OTC medications and the need for multiple treatments in special populations, such as the elderly people, it is essential that the issue of drug interactions is properly evaluated. New OACs offer significant potential advantages to the field of venous thromboprophylaxis, but we should not fail to appreciate their lack of extensive clinical experience.

[A new deal with new anticoagulants?]

The anticoagulant market has been very active recently with the development of new compounds including injectable anti-Xa such as fondaparinux, already available, and idraparinux, already replaced by its new biotynilateed form, and new oral drugs which can be divided into anti-IIa with dabigatran already available, and anti-Xa, such as the recently marketed rivaroxaban and apixaban still in the development stage. Others are coming forward. The competition is strong and the place for each drug remains to be determined. This review discusses these new anticoagulants in terms of efficacy and tolerance based on data in the literature. These recent reports mainly concern prophylaxis for orthopedic surgery but also consider treatment of deep venous thrombosis. The results of studies in heart patients have raised much curiosity since they will be determinant in the future use of innovating compounds, which could replace current oral anticoagulants. This will be upcoming but not yet for tomorrow.

New anticoagulants for the prevention of venous thromboembolism

Anticoagulant drugs have an essential role in the prevention and treatment of thromboembolic diseases. Currently available anticoagulants substantially reduce the incidence of thromboembolic events in a number of clinical conditions. However, these agents have limitations that strengthen the case for the development of new anticoagulants. An ideal anticoagulant should be at least as effective as those currently in use, as well as safe, simple to use, and widely applicable.The majority of new anticoagulants currently under investigation are small molecules with a selective and direct anti-Xa or antithrombin action, allowing oral administration in fixed doses. These new agents are in different phases of clinical development. The anti-Xa agent rivaroxaban and the antithrombin agent dabigatran are already available for the prophylaxis of venous thromboembolism in some countries. Apixaban is in an advanced phase of clinical development and several anti-Xa agents are currently approaching phase III clinical trials. Promising results in terms of efficacy and safety profiles have been obtained with these agents in different clinical conditions. Differences in pharmacokinetics and pharmacodynamics could offer the potential for individualized anticoagulant therapies in the near future.

Rivaroxaban and dabigatran etexilate: two new oral anticoagulants for extended postoperative prevention of venous thromboembolism after elective total hip arthroplasty

Extended thromboprophylaxis is vital in patients undergoing total hip arthroplasty (THA) because of the prolonged risk of venous thromboembolism (VTE). Despite evidence that extended prophylaxis can reduce the incidence of symptomatic VTE in this high-risk patient population and the evidence-based guideline recommendations, a large proportion of patients still do not receive an adequate duration of thromboprophylaxis. This is partly due to the limitations of conventional anticoagulants, such as the subcutaneous route of administration or the requirement for routine coagulation monitoring and dose adjustment. New oral anticoagulants (such as the direct thrombin inhibitor dabigatran etexilate and the Factor Xa inhibitor rivaroxaban) could address the current unmet need. Phase III clinical studies in VTE prevention in patients undergoing THA and total knee arthroplasty (TKA) showed that dabigatran etexilate was non-inferior to the EU regimen of enoxaparin, but did not achieve non-inferiority to the US regimen of enoxaparin. In contrast, rivaroxaban demonstrated superiority to both enoxaparin regimens for the prevention of VTE after THA and TKA, without a significant increase in major bleeding rates. Their convenient, once-daily, fixed dosing, with no need for routine coagulation monitoring, could facilitate adherence to evidence-based guideline recommendations of extended thromboprophylaxis after THA.

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.

Newer anticoagulants in 2009

Several newer anticoagulants are under clinical development. Recently two of them, Dabigatran etexilate/Pradaxa. and Rivaroxaban/Xarelto obtained marketing authorization in Europe and Canada for the prevention of thromboembolic events following major orthopedic surgery such as total hip and knee replacement. The results of Phase III clinical studies in thromboprophylaxis in major orthopedic surgery are highlighted and discussed in detail. Ongoing Phase II and III clinical trials assess their efficacy in the secondary prevention and treatment of deep vein thrombosis and pulmonary embolism, and in the long-term prevention of stroke in patients with non-valvular atrial fibrillation and in combination with aspirin and clopidogrel in patients with acute coronary syndromes. Many other small antithrombotic molecules including a new generation of low molecular weight heparins, are currently in different stages of clinical development. In addition to being administered orally, the newer anticoagulant agents have a more balanced benefit/risk ratio and wider therapeutic window. They have a rapid onset of action, a predictable anticoagulant effect that does not require routine laboratory monitoring. They have minor food and drug interactions, including those with cytochrome P450 and P.gp. They are highly specific and targeted to a single coagulation factor, and could carry similar or less hemorrhagic risks compared to the older anticoagulant agents. Finally, they may be used in a broader variety of patients, especially the medically ill patients with advanced cancer, and the elderly without any dosage adjustment, regardless of the patient age, gender, body weight, or in patients with mild renal impairment. Their use in the general world will hopefully confirm the promising results of clinical trials.

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.

Venous thromboembolism: a clinical review

Venous thromboembolism (VTE), including deep vein thrombosis (DVT) and pulmonary embolism, represents a significant source of morbidity and mortality. It is readily diagnosed with noninvasive modalities when there is a clinical suspicion. Most patients presenting with signs and symptoms of DVT have well-known risk factors, such as a history of VTE, malignancy, recent illness, or immobilization. A subset of individuals with idiopathic VTE have no readily identifiable risk factors. Therapeutic anticoagulation is the cornerstone of management in all patients with VTE. Adjunctive measures, such as thrombolysis and the use of vena cava filters, are indicated in select cases. The ideal duration of anticoagulation is unknown, but is often maintained long-term in patients with acquired or inherited thrombophilia. Warfarin is the only oral anticoagulant approved by the US Food and Drug Administration. Warfarin carries a substantial annual risk of bleeding complications, requires ongoing monitoring, and has extensive drug-drug interactions, which are causes for concern in patients requiring long-term anticoagulation. Alternative oral anticoagulants, such as direct thrombin inhibitors and factor Xa inhibitors, are subjects of active research in alternative agents for oral anticoagulation, and have been recently approved for prophylaxis in Canada and the European Union.