New anticoagulants for the prevention of venous thromboembolism

[Cost-effectiveness analysis of apixaban compared to dabigatran in the prevention of venous thromboembolism in patients subjected to total knee or hip replacement]

OBJECTIVE

Cost-effectiveness analysis of apixaban vs. dabigatran in preventing venous thromboembolism (VTE) in total knee (TKR) or hip (THR) replacement.

METHODS

Model with two periods: post-prophylaxis period of 90 days (short term) and 5 years (Markov). VTE complications (distal and proximal deep vein thrombosis, pulmonary embolism, bleeding and post-thrombotic syndrome) were included. The comparative efficacy was obtained from a meta-analysis, and the costs from Spanish sources. An annual discount rate of 3.5% for costs and benefits was applied.

RESULTS

According to the meta-analysis, the relative risk (RR) of VTE or death, compared with enoxaparin, was lower with apixaban than with dabigatran in TKR (RR 0.89, 95% CI 0.32 to 1.65 and RR 1.35, 95% CI, 0.19 to 3.39) and THR (RR 0.35, 95% CI, 0.05 to 2.51 and RR 0.89, 95% CI 0.22 to 3.21, respectively). In the short term, there were more life years (LYG) and more quality-adjusted life years (QALY) per patient in TKR (0.2037; 0.1908) and THR (0.2417; 0.1921) with apixaban than with dabigatran (0.1818; 0.1901 and 0.2345; 0.1918, respectively) were obtained. With apixaban lower costs per patient in TKR (-14 €) were generated, so it was the dominant treatment. Additional costs (15 €) could be incurred in THR, with a cost per LYG of 2,083 € and 50,000 € per QALY gained. In 5 years, apixaban was cheaper and more effective in both TKR and THR.

CONCLUSIONS

According to this study, apixaban was shown to be a cost-effective treatment compared with dabigatran for VTE prevention.

Safety of fondaparinux versus enoxaparin after TKA in Japanese patients

Fondaparinux and enoxaparin are useful for preventing venous thromboembolism after total knee arthroplasty (TKA), but both drugs have associated complications. The purpose of this study was to clarify the risks associated with use of these drugs in Japanese patients who underwent TKA.A total of 575 patients (935 knees) underwent TKA and were retrospectively reviewed; 277 patients (454 knees) were treated with fondaparinux and 298 patients (481 knees) were treated with enoxaparin. The authors investigated the incidences of deep venous thrombosis of the lower limbs and pulmonary embolism to evaluate venous thromboembolism, knee enlargement compared with the preoperative size, incidence of subcutaneous knee hematoma, and other complications. No significant differences were observed between the 2 drugs regarding the incidences of deep venous thrombosis and pulmonary embolism. However, fondaparinux use resulted in knee enlargement (P<.0005) and subcutaneous hematoma of the knee (P=.035) significantly more often than enoxaparin use. Conversely, enoxaparin use significantly caused the elevation of alanine aminotransferase (one of the liver enzymes) at a higher rate than fondaparinux (30.1% vs 8.3%, respectively; P<.0001). However, the increased alanine aminotransferase levels were transient, and no patient exhibited symptoms of abnormal liver function, such as jaundice or cutaneous pruritus.Fondaparinux and enoxaparin were both effective in preventing venous thromboembolism in Japanese patients undergoing elective TKA. However, both drugs had some adverse effects. It is important to be aware of these potential risks when prescribing these drugs.

Direct thrombin and factor Xa inhibition for stroke prevention in patients with atrial fibrillation

Nonvalvular atrial fibrillation (AF) is the most common clinically significant cardiac arrhythmia occurring in patients in the United States. The primary clinical consequence of AF is an increase in the risk and severity of strokes. Treatment guidelines recommend anticoagulation therapy for most patients with AF. One risk-stratification scheme, the CHADS2 index, is simple and widely used to determine the management of patients with AF in regard to stroke prevention. However, new schemes, such as CHA2DS2-VASc, further refine risk stratification to identify patients who would obtain a net clinical benefit from a particular management strategy, thus improving the quality of management. For patients with AF for whom oral anticoagulation (OAC) is advisable, vitamin K antagonist (VKA) therapy is well established and effective. However, OAC with VKAs presents challenges to prescribers and patients in maintaining therapeutic efficacy. Novel OACs may offer alternatives to VKAs. Dabigatran etexilate, a direct thrombin inhibitor, was approved by the US Food and Drug Administration (FDA) in 2010 for reducing the risk of stroke and systemic embolism in patients with nonvalvular AF. The activated factor X (factor Xa) inhibitor rivaroxaban was recently approved by the FDA both for prophylaxis of deep vein thrombosis, which may lead to pulmonary embolism in patients undergoing knee or hip arthroplasty, and for reducing the risk of stroke and systemic embolism in patients with nonvalvular AF. Apixaban, another factor Xa inhibitor, was recently shown to be effective for stroke prevention in patients with nonvalvular AF. This article reviews clinical considerations regarding new agents that may offer alternatives to VKA therapy for the prevention of stroke in patients with AF.

Prevention and treatment of venous thromboembolism with new oral anticoagulants: a practical update for clinicians

Traditional anticoagulants, such as warfarin and enoxaparin, have several limitations, including parenteral administration, need for laboratory monitoring, and ongoing dose adjustment, which may limit optimal patient care. Newer oral anticoagulants, such as direct thrombin inhibitors (e.g., dabigatran etexilate) and direct factor Xa inhibitors (e.g., rivaroxaban, apixaban, and edoxaban), have been developed to overcome these drawbacks, and thereby improve patient care. Several of these agents have been approved for use in the prevention and treatment of venous and/or systemic thromboembolism. The objective of this paper is to provide an overview of the available clinical trial data for these new oral anticoagulants in the prevention and treatment of venous thromboembolism and a practical update for clinicians.

Managing anticoagulation for atrial fibrillation: current issues and future strategies

Although warfarin is superior to aspirin in reducing the risk of stroke in patients with atrial fibrillation, it can increase major bleeds. Hence, physicians stratify patients according to stroke risk to ensure a net benefit. In this review, the CHA(2) DS(2) -VASc stratification scheme used in the latest European Society of Cardiology (2010/12) guidelines will be explained. The greater sensitivity of this scheme, compared to the previous CHADS(2) , more closely delineates patients for whom warfarin is appropriate. The review also anticipates that there will be a wider range of patients who may benefit from the new oral anticoagulants, which show similar or superior efficacy and/or safety to warfarin with a significant reduction in intracranial haemorrhage and do not require routine coagulation monitoring. The role of conventional and new anticoagulant options will also be discussed.

Therapeutic potential of apixaban in the prevention of venous thromboembolism in patients undergoing total knee replacement surgery

Anticoagulant prophylaxis for preventing venous thromboembolism (VTE) is a worldwide established procedure in hip and knee replacement surgery. Despite available anticoagulant prophylaxis, patients who undergo total knee arthroplasty (TKA) have a high incidence of venous VTE. In spite of their proven efficacy, the currently available anticoagulants have limitations that driven to develop new oral agents that directly target specific factors in the coagulation cascade, such as direct thrombin inhibitors and direct Factor Xa inhibitors, in an attempt to overcome some of the drawbacks with the traditional agents. Apixaban is a potent, selective direct inhibitor of the coagulation factor Xa, recently approved in Europe for the prevention of venous thromboembolism (VTE) in adult patients after total hip replacement (THR) or total knee replacement (TKR) surgery. Apixaban has been extensively studied worldwide in about 12,000 patients in four clinical studies that have demonstrated the efficacy and safety of apixaban respect to enoxaparin for the prevention of thromboembolism after major orthopedic surgery. Three of these trials involved 7,337 patients who undergo TKR: one phase II trial (APROPOS Study) and two large phase III trials (ADVANCE 1 and ADVANCE 2 Studies). ADVANCE 1 demonstrated that when compared with enoxaparin 30 mg twice daily for efficacy, apixaban did not meet the prespecified statistical criteria for noninferiority, but its use was associated with lower rates of clinically relevant bleeding. ADVANCE 2 showed that apixaban was superior to the European standard dose of enoxaparin of 40 mg once daily in term of efficacy, with a similar incidence of major bleeding. This review focuses the clinical efficacy and tolerability of oral apixaban for the prevention of VTE in adult patients following TKR surgery.

Role of new anticoagulants for the prevention of venous thromboembolism after major orthopaedic surgery and in hospitalised acutely ill medical patients

Anticoagulation therapy for the prevention of venous thromboembolic events is indicated in patients after major orthopaedic surgery and in hospitalised acutely ill medical patients, who have a high or moderate risk of venous thromboembolism (VTE), respectively. Clinical trials have clearly demonstrated that short-term anticoagulation reduces the risk of VTE in these patient groups and that longer-term anticoagulation is beneficial for some indications. Evidence-based guidelines for thromboprophylaxis have been developed based on these studies. However, despite these guidelines, thromboprophylaxis is still underused, or used suboptimally, in many patients. This is, in part, because of the limitations of traditional anticoagulants such as unfractionated heparin, low- molecular-weight heparin, synthetic pentasaccharides, and vitamin K antagonists. Newer oral anticoagulants, such as rivaroxaban, apixaban, and dabigatran etexilate, have certain advantages over traditional agents. They can be administered orally at a fixed dose without routine coagulation monitoring and have minimal food and drug interactions. These characteristics may result in better adherence to guidelines and improved patient outcomes. This review provides an overview of phase III clinical trial data for these newer anticoagulants in major orthopaedic surgery and in hospitalised acutely ill medical patients, and discusses their potential for extended use in the post-hospital discharge setting. All three newer oral anticoagulants are approved in many countries for the prevention of VTE after hip replacement or knee replacement surgery in adult patients, and it is likely that these drugs will contribute considerably towards reducing the substantial healthcare burden associated with VTE.

Fluorogenic peptide-based substrates for monitoring thrombin activity

The synthesis of a series of peptides containing C-terminal 7-amino-4-methylcoumarin (AMC) for use in the thrombin generation test (TGT) is described. The lead structure in this project was H-Gly-Gly-Arg-AMC, of which the water solubility and kinetic parameters (K(M) and k(cat)) are greatly improved over those of the substrate in current use in the TGT: Cbz-Gly-Gly-Arg-AMC. A series of N-terminally substituted Gly-Gly-Arg-AMC derivatives were synthesized, as well as implementation of structural changes at either the P(2) or P(3) position of the peptide backbone. Furthermore, two substrates were synthesized that have structural similarities to the chromogenic thrombin substrate SQ68 or that contain a 1,2,3-triazole moiety in the peptide chain, mimicking an amide bond. To determine the applicability of newly synthesized fluorogenic substrates for monitoring continuous thrombin generation, the K(M) and k(cat) values of the conversion of these fluorogenic substrates by thrombin (FIIa) and factor Xa (FXa) were quantified. An initial selection was made on basis of these data, and suitable substrates were further evaluated as substrates in the thrombin generation assay. Assessment of the acquired data showed that several substrates, including the SQ68 derivative Et-malonate-Gly-Arg-AMC and N-functionalized Gly-Gly-Arg-AMC derivatives, are suitable candidates for replacement of the substrate currently in use.

Apixaban and rivaroxaban safety after hip and knee arthroplasty: a meta-analysis

Direct experimental safety comparisons of Xa coagulation factor direct inhibitors, apixaban and rivaroxaban, on their approved therapeutic indications have not been identified. Due to recently raised safety concerns, a meta-analysis was carried out pooling data from studies identified on a Medline and Cochrane Library search in order to better evaluate the safety profile of both drugs. Abstracts from scientific meetings were also searched from 2003 to 2011. Primary and secondary outcome measures were major bleeding and total bleeding, respectively. Relative risks (RRs) were estimated using random effects models and statistical heterogeneity was estimated with I(2) statistics. Of the 160 screened publications, 12 clinical trials were included in which enoxaparin was the active control. For knee arthroplasty, apixaban was associated with significantly fewer major bleeding events (6496 patients, RR 0.56, 95% confidence interval [CI] 0.32-0.96) and fewer total bleeding events (6496 patients, RR 0.81, 95% CI 0.67-0.97). There were no significant differences in the incidence of major bleeding events (5699 patients, RR 1.40, 95% CI 0.56-3.52) or in the incidence of total bleeding events for rivaroxaban (5699 patients, RR 1.09, 95% CI 0.91-1.30). No differences were found when thromboprophylaxis after hip replacement was the case. Apixaban seems to be associated with a lower risk of the incidence of hemorrhagic events after total knee arthroplasty. For hip arthroplasty, no differences were found between the studied drugs.

Therapeutic potential of apixaban in the prevention of venous thromboembolism in patients undergoing total knee replacement surgery

BACKGROUND

Apixaban is a novel oral factor Xa inhibitor that recently completed evaluation in clinical trials for its use in the prevention of venous thromboembolism (VTE) in patients undergoing hip or knee replacement surgery. Its manufacturers are currently seeking approval for these indications in the European Union and a rolling submission is in process in the United States.

SCOPE

This article reviews published data on the efficacy and safety profile of apixaban in patients undergoing total knee arthroplasty (TKA). For this review, the authors searched PubMed for English language clinical trial articles involving the use of apixaban in human subjects published through July 11, 2011. The key words 'apixaban' and 'total knee arthroplasty/replacement' were used. The review focused on clinical trials, but other articles were reviewed for relevant information.

FINDINGS

One dose-finding phase II trial demonstrated apixaban's efficacy and a dose of 2.5 mg twice daily was established for future investigation. Two phase III clinical trials have been completed with apixaban in TKA patients (ADVANCE-1 and ADVANCE-2). In ADVANCE-1, apixaban did not meet the pre-specified non-inferiority criteria, while in ADVANCE-2, apixaban met the non-inferiority criteria when compared to enoxaparin, and had a similar safety profile.

CONCLUSION

Apixaban is a promising new agent awaiting regulatory approval for its use in thromboprophylaxis after TKA.

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.

Pharmacogenetics of coumarin dosing: prevalence of CYP2C9 and VKORC1 polymorphisms in the Lebanese population

BACKGROUND

Polymorphisms in the genes encoding the cytochrome P450 2C9 enzyme (CYP2C9) and the vitamin K epoxide reductase (VKORC1) are known to contribute to variability in sensitivity to coumarins. Patients with certain common genetic variants of CYP2C9 (*2 & *3) or a VKORC1 polymorphism (-1639A Allele) require a lower dose of coumarin and are also at higher risk for over-anticoagulation and serious bleeding. In August 2007, the FDA label for warfarin was updated to highlight the benefit of genetic testing to predict warfarin response.

AIM

Since the prevalence of these variants in the Lebanese population has not yet been reported, our aim was to determine the genotypes of CYP2C9 and VKORC1 in our population and to compare allele frequencies with previous findings from other ethnic groups.

MATERIALS AND METHODS

CYP2C9 (*1/*2/*3) and VKORC1 (*A/*G) allelic variants were assessed by polymerase chain reaction-restriction fragment length polymorphism assays in a diversified sample of 161 unrelated healthy Lebanese volunteers.

RESULTS

The allele frequencies of CYP2C9 *2 and *3 were 0.112 and 0.096 respectively, whereas VKORC1-1639A was 0.528. Carriers of the CYP2C9 *2 or *3 represented 34.2% of the subjects, whereas those of the VKORC1-1639A represented 73.9%.

CONCLUSION

Our data show no significant difference in the frequency of CYP2C9 allelic variants when compared to the Caucasian population, whereas the allelic frequency of VKORC1-1639A was very high. Over 50% of the Lebanese population seem to be carrying more than two independent risk alleles, and is therefore potentially at high risk of over-anticoagulation.

Dabigatran etexilate: a novel oral thrombin inhibitor for thromboembolic disease

OBJECTIVE

To evaluate the efficacy and safety of dabigatran etexilate, approved by the Food and Drug Administration (FDA) in October 2010 for the prevention of cardioembolic stroke in patients with atrial fibrillation; potential off-label use is treatment and prevention of venous thromboembolic disorders.

DATA SOURCES

Literature was accessed through MEDLINE (1977-April 2011) and International Pharmaceutical Abstracts (1977-April 2011) using the terms dabigatran, dabigatran etexilate, BIBR 1048, direct thrombin inhibitor, anticoagulant, and thromboembolism. In addition, US government Web sites, including clinicaltrials.gov and fda.gov, were reviewed for pertinent information. Lastly, reference citations from publications identified in the initial search were reviewed.

STUDY SELECTION AND DATA EXTRACTION

All English-language articles identified from the data sources were evaluated. For the evaluation of clinical efficacy and safety, only Phase 2 and 3 studies are included in this review.

DATA SYNTHESIS

In 6 published Phase 3 trials to date, dabigatran has exhibited a similar efficacy and safety profile to that of comparator drugs, including dose-adjusted warfarin and enoxaparin, at various dosages. In the largest of these trials, RE-LY (Randomized Evaluation of Long-Term Anticoagulation Therapy), dabigatran was at least as effective as dose-adjusted warfarin in reducing stroke or systemic embolism. Overall bleeding risks were similar; however, dabigatran may be associated with a lower incidence of intracranial bleeding and hemorrhagic stroke but a higher incidence of gastrointestinal bleeding. Although dabigatran is not approved for venous thromboembolism (VTE) prevention or treatment, results of the RE-MODEL and RE-NOVATE trials suggest similar efficacy to once-daily dosing of enoxaparin 40 mg but inferior efficacy to the FDA-approved twice-daily dosing of enoxaparin 30 mg in the RE-MOBILIZE trial.

CONCLUSIONS

Dabigatran is an effective and safe alternative to oral vitamin K antagonists for stroke prevention in patients with nonvalvular atrial fibrillation, with fewer drug interactions and monitoring requirements. Additionally, dabigatran may be a viable alternative to enoxaparin in VTE prevention and warfarin in VTE treatment, although current trial data are limited.

[Pulmonary circulation: what has 2010 brought?]

In both thromboembolic disease and pulmonary hypertension, 2010 has been a prodigious year for interesting publications. Some data have helped to elucidate the factors associated with a greater risk of thromboembolic disease, such as long journeys and certain polymorphisms. New recommendations on diagnosis have been made, giving a greater role to computed tomography angiography. Magnetic resonance imaging is also gaining ground. More accurate risk evaluation is one of the objectives of the new guidelines of the European Society of Cardiology, which substitute some terms such as massive or submassive for high- and low-risk. Maintaining anticoagulation indefinitely in idiopathic pulmonary thromboembolism is recommended. Evidence on the efficacy of new drugs such as rivaroxaban, dabigatran and indraparinux is beginning to appear. In pulmonary hypertension, smoking seems to play a role as a risk factor. Some registries indicate that new treatments have not improved survival. Greater knowledge has been gained of the role of inflammation in the pathogenesis of the disease and a Spanish study supports the role of the 6-minute walk test in patient evaluation. Some drugs are highlighted in the literature. Imatinib is promising but probably only in some patients. Riociguat provides good results and inhaled treprostinil has emerged as a new option.