Interpretation of endpoints in a network meta-analysis of new oral anticoagulants following total hip or total knee replacement surgery

CRISTAL (a cluster-randomised, crossover, non-inferiority trial of aspirin compared to low molecular weight heparin for venous thromboembolism prophylaxis in hip or knee arthroplasty, a registry nested study): statistical analysis plan

BACKGROUND

This a priori statistical analysis plan describes the analysis for CRISTAL.

METHODS

CRISTAL (cluster-randomised, crossover, non-inferiority trial of aspirin compared to low molecular weight heparin for venous thromboembolism prophylaxis in hip or knee arthroplasty, a registry nested study) aims to determine whether aspirin is non-inferior to low molecular weight heparin (LMWH) in preventing symptomatic venous thromboembolism (VTE) following hip arthroplasty (HA) or knee arthroplasty (KA). The study is nested within the Australian Orthopaedic Association National Joint Replacement Registry. The trial was commenced in April 2019 and after an unplanned interim analysis, recruitment was stopped (December 2020), as the stopping rule was met for the primary outcome. The clusters comprised hospitals performing > 250 HA and/or KA procedures per annum, whereby all adults (> 18 years) undergoing HA or KA were recruited. Each hospital was randomised to commence with aspirin, orally, 85-150 mg daily or LMWH (enoxaparin), 40 mg, subcutaneously, daily within 24 h postoperatively, for 35 days after HA and 14 days after KA. Crossover was planned once the registration target was met for the first arm. The primary end point is symptomatic VTE within 90 days. Secondary outcomes include readmission, reoperation, major bleeding and death within 90 days, and reoperation and patient-reported pain, function and health status at 6 months. The main analyses will focus on the primary and secondary outcomes for patients undergoing elective primary total HA and KA for osteoarthritis. The analysis will use an intention-to-treat approach with cluster summary methods to compare treatment arms. As the trial stopped early, analyses will account for incomplete cluster crossover and unequal cluster sizes.

CONCLUSIONS

This paper provides a detailed statistical analysis plan for CRISTAL.

TRIAL REGISTRATION

Australian and New Zealand Clinical Trials Registry ACTRN12618001879257 . Registered on 19/11/2018.

CRISTAL: protocol for a cluster randomised, crossover, non-inferiority trial of aspirin compared to low molecular weight heparin for venous thromboembolism prophylaxis in hip or knee arthroplasty, a registry nested study

INTRODUCTION

Venous thromboembolism (VTE) is a serious complication following hip arthroplasty (HA) and knee arthroplasty (KA). This study aims to determine whether aspirin is non-inferior to low molecular weight heparin (LMWH) in preventing symptomatic VTE following HA and KA.

METHODS AND ANALYSIS

This is a cluster randomised, crossover, non-inferiority, trial nested within the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR). The clusters will consist of Australian hospitals performing at least 250 HA and/or KA procedures per annum. All adult patients undergoing HA or KA will be included. The intervention will be aspirin, orally, 85-150 mg daily. The comparator will be LMWH (enoxaparin) 40 mg, subcutaneously, daily. Both drugs will commence within 24 hours postoperatively and continue for 35 days after HA and 14 days after KA. Each hospital will be randomised to commence with aspirin or LMWH and then crossover to the alternative treatment after meeting the recruitment target. Data will be collected through the AOANJRR via patient-reported surveys. The primary outcome is symptomatic VTE within 90 days post surgery, verified by AOANJRR staff. The primary analysis will include only patients undergoing elective primary total hip arthroplasty and total knee arthroplasty for osteoarthritis. Secondary outcomes will include symptomatic VTE for all HA and KA (including partial and revision) within 90 days, readmission, reoperation, major bleeding and death within 90 days and reoperation, death and patient-reported pain, function and health status at 6 months. If aspirin is found to be inferior, a cost-effectiveness analysis will be conducted. The study will aim to recruit 15 562 patients from 31 hospitals.

ETHICS AND DISSEMINATION

Ethics approval has been granted. Trial results will be submitted for publication. The trial is registered with the Australian New Zealand Clinical Trials Registry (ACTRN12618001879257, pre-results) and is endorsed by the Australia and New Zealand Musculoskeletal Clinical Trials Network.

Klinische Studien zu neuen direkten oralen Antikoagulanzien

Um die Wirksamkeit und Verträglichkeit neuer direkter oraler Antikoagulanzien (DOAK) zu vergleichen, müssten idealerweise eine direkte Gegenüberstellung der Substanzen in klinischen Studien durchgeführt werden. Auf Grund des logistischen und finanziellen Aufwandes wird dies aber in absehbarer Zeit nicht geschehen. Indirekte Vergleiche, auch Netzwerkanalysen (NMA) genannt, lassen sich mit den vorliegenden Studien zwischen den DOAKs vornehmen. In der postoperativen Phase nach Knie- und Hüftgelenkersatz und bei Patienten mit Vorhofflimmern sind derzeit diese Vergleich möglich. Indirekte Vergleiche sind jedoch auch mit Einschränkungen behaftet.

Diese Arbeit gibt eine Übersicht der aktuell vorliegenden NMAs und versucht, deren Ergebnisse mit der Pharmakologie der DOAKs und den methodischen Problemen von NMAs zu beleuchten.

Thromboprophylaxis with enoxaparin and direct oral anticoagulants in major orthopedic surgery and acutely ill medical patients: a meta-analysis

Subjects undergoing major orthopedic surgery and acutely ill hospitalized medical patients represent a population at medium-high risk for venous thromboembolism (VTE). They are treated with low molecular weight heparin (LMWH) and direct oral anticoagulants [DOACs] for VTE prevention. We conducted a meta-analysis of phase III randomized clinical trials evaluating LMWH enoxaparin versus DOACs for prophylaxis of VTE by combining studies including patients undergoing elective total hip and knee replacement surgery, and acutely ill hospitalized medical subjects. Studies were searched using PubMed, MEDLINE, and EMBASE databases until December 2016. Differences in clinical outcomes for efficacy and safety endpoints between treatment groups were expressed as risk differences with 95% confidence intervals (95% CI), using random effects regression models. Fourteen RCTs were considered (60,467 subjects). Overall mortality, symptomatic deep venous thrombosis, non-fatal pulmonary embolism (PE) major bleeding (MB) and clinically relevant non-major bleeding (CRNMB) are not different between treatment regimens. Treatment with LMWH enoxaparin is associated with a lower risk of fatal PE plus VTE-related death compared therapy with DOACs (RD = 0.040%, 95% CI 0.001-0.080%, p = 0.0434). Subgroup analysis shows an incidence of MB (RD = 0.181%, 95% CI 0.029-0.332%, p = 0.0033) and CRNMB (RD = 0.546%, 95% CI 0.009-1.082%, p = 0.0462) in patients treated with 40 mg OD enoxaparin compared to DOACs. In major orthopedic surgery and acutely ill hospitalized medical patients, DOACs do not offer clear advantages in terms of clinical efficacy compared to enoxaparin. The advantage of the latter in terms of major and CRNMB, when used at a dose of 40 mg, is statistically significant, but small in terms of clinical relevance.

Benefit–risk profile of non-vitamin K antagonist oral anticoagulants in the management of venous thromboembolism

The prevention and treatment of venous thromboembolism (VTE) remains a clinical challenge, primarily owing to drawbacks associated with the use of heparins and vitamin K antagonists (VKAs). These and other factors, including a growing elderly population, mean that VTE presents a continuing burden to patients and physicians. Anticoagulant therapy is a fundamental approach for VTE management. Non- VKA oral anticoagulants, including the factor Xa inhibitors apixaban, edoxaban and rivaroxaban, and the thrombin inhibitor dabigatran, have been studied in phase III trials across a spectrum of thromboembolic disorders. These agents offer simplified care, with similar or improved efficacy and safety outcomes compared with heparins and vitamin K antagonists. There are several factors a physician must consider when prescribing an anticoagulant. An important consideration with all anticoagulant use is bleeding risk, especially in high-risk groups such as the elderly or those with renal impairment or cancer. In orthopaedic patients, other risks include a need for surgical revision or blood transfusion, or wound complications. Therefore, the clinical benefits of an anticoagulant should ideally be balanced with any risks associated with the therapy. Quantitative benefit–risk assessments are lacking, and owing to differences in trial design the non-VKA oral anticoagulants cannot be compared directly. Based on trial and “reallife” data, this review will summarise the clinical data for the non-VKA oral anticoagulants in the prevention and treatment of VTE, focusing on the balance between the benefits and risks of anticoagulation with these drugs, and their potential impact on VTE management.

Comparative efficacy and safety of anticoagulants for prevention of venous thromboembolism after hip and knee arthroplasty

Background and purpose - New oral anticoagulants have been developed to prevent venous thromboembolism (VTE) after knee or hip arthroplasty. Although there have been several network meta-analyses (NMA) to compare different regimens, an NMA including 2 different enoxaparin doses and edoxaban has not been performed. Methods - Standard NMA for fondaparinux, dabigatran, rivaroxaban, apixaban, edoxaban, and enoxaparin was performed. Outcome variables included a composite of total VTE and major/clinically relevant bleeding. The rank probabilities of each treatment outcome were summarized by the surface under the cumulative ranking curve. Results - Fondaparinux, rivaroxaban, and apixaban were associated with a reduced risk of VTE compared with enoxaparin, while dabigatran was not. None of these 3 drugs increased bleeding compared with enoxaparin 30 mg twice daily. However, fondaparinux and rivaroxaban increased bleeding compared with enoxaparin 40 mg once daily, while apixaban did not. Apixaban was even associated with decreased major/clinically relevant bleeding compared with enoxaparin 30 mg twice daily or 40 mg once daily. When edoxaban was included in the NMA, edoxaban decreased VTE and did not increase bleeding compared with enoxaparin. Interpretation - A higher efficacy of fondaparinux and rivaroxaban compared with enoxaparin was associated with increased bleeding tendency, while apixaban was superior to enoxaparin regarding both efficacy and safety. A clustered ranking plot showed that apixaban might be the most preferred regarding efficacy and safety. However, our results were driven by indirect statistical inference and were limited by the heterogeneity of the bleeding outcome definitions, drug initiation and continuation, and different surgery types.

Direct Oral Anticoagulants Vs. Enoxaparin for Prevention of Venous Thromboembolism Following Orthopedic Surgery: A Dose-Response Meta-analysis

We carried out a dose–response model‐based meta‐analysis to assess venous thromboembolism (VTE) and bleeding with factor Xa (FXa) inhibitors (apixaban, edoxaban, rivaroxaban) and a thrombin inhibitor (dabigatran) compared with European (EU) (40 mg q.d.) and North American (NA) (30 mg Q12H) dose regimens of a low molecular weight heparin (enoxaparin) following orthopedic surgery. Statistically significant differences in both VTE and bleeding outcomes were found between the NA and EU doses of enoxaparin, with odds ratios (95% confidence interval) for the NA vs. EU dose of 0.73 (0.71–0.76) and 1.20 (1.14–1.29) for total VTE and major bleeding, respectively. At approved doses, estimated odds ratios vs. both doses of enoxaparin for the three FXa inhibitors (range: 0.35–0.75 for VTE; 0.76–1.09 for bleeding) compared with those for dabigatran (range: 0.66–1.21 for VTE; 1.10–1.38 for bleeding) suggested generally greater efficacy and less bleeding for the FXa inhibitors.

Laboratory determination of old and new targeted anticoagulant agents for prevention of bleeding and thrombotic events in cancer patients

A two-fold prolongation of activated partial thromboplastin time (APTT) is established as therapeutic range for therapy with unfractionated heparin, hirudin and argatroban. The international normalized ratio (INR) of 2 to 3 is required to maintain anticoagulation in the therapeutic range of vitamin K antagonists. The therapeutic range of anti-factor Xa activity during therapy with low-molecular weight heparins and danaparoid are less well and of direct oral anticoagulants (DOAC) poorly defined. The relation of aPTT and INR values to thrombotic and bleeding events are well established despite a large variation of values in affected patients. The relation of coagulation values of the other anticoagulants to clinical events is open. The value of determination in cancer patients is higher because of the increased risk for thrombotic and bleeding events of this patient group. Several activities are currently undertaken to certify methods for in vitro diagnostic testing for DAOCs.

Safety and efficacy of new oral anticoagulants and low-molecular-weight heparins compared with aspirin in patients undergoing total knee and hip replacements

BACKGROUND

There has been much debate recently on the best type of thromboprophylaxis following elective total joint replacement surgery.

OBJECTIVE

This study aims to compare rates of venous thromboembolism (VTE), gastro-intestinal (GI) bleeding and mortality events, with use of new oral anticoagulants (NOAC) or low-molecular-weight heparins (LMWHs) compared with aspirin in patients undergoing total joint replacement.

METHODS

A population-based retrospective cohort study was performed using the Clinical Practice Research Datalink. Patients ≥18 years of age who had undergone total knee (n = 3261) or hip replacement (THR (n = 4016)) between 2008 and 2012 were included. Within this population, three cohorts were selected, based on their first prescription within the 35-day period after surgery: use of NOACs only, LMWHs only and aspirin only. Incidence rates were calculated, and Cox proportional hazard models were fitted to estimate the risk of VTE, GI bleeding and all-cause mortality with the use of NOACs and LMWHs compared with aspirin use after total knee replacement and THR. We statistically adjusted our analyses for lifestyle factors, comorbidities and concomitant drug use.

RESULTS

Total knee replacement and THR patients currently on LMWHs had higher risk of VTE (HR = 17.2 (6.9-43.0) and HR = 39.5 (18.0-87.0), respectively), GI bleeding (HR = 20.9 (1.9-232.3) and HR = 2.0 (0.2-17.2), respectively) and all-cause mortality (HR = 4.3 (1.7-12.4) and HR = 4.0 (2.4-6.7), respectively). NOAC use was associated with an increased risk of GI bleeding in patients undergoing THR surgery.

CONCLUSIONS

In contrast to previous studies, we found an increased risk of VTE, GI bleeding and all-cause mortality with the use of LMWHs compared with aspirin. Risk of GI bleeding was increased with the use of NOACs compared with aspirin use after THR surgery. Copyright © 2016 John Wiley & Sons, Ltd.

Oral direct factor Xa inhibitor versus enoxaparin for thromboprophylaxis after hip or knee arthroplasty: Systemic review, traditional meta-analysis, dose-response meta-analysis and network meta-analysis

OBJECTIVES

To analyze the efficacy and safety of direct factor Xa inhibitors for thromboprophylaxis after total hip or knee replacement. To delineate the dose response effect of direct factor Xa inhibitors. To compare the efficacy between any two direct factor Xa inhibitors.

DESIGN

Systemic review, traditional meta-analysis, dose-response meta-analysis and network meta-analysis.

DATA SOURCE

PubMed, EMBASE and Cochrane Library.

STUDY SELECTION

Randomized controlled trials of rivaroxaban, apixaban, betrixaban, darexaban and edoxaban were compared with enoxaparin for thromboprophylaxis after total hip or knee replacement. Two reviewers independently checked the quality of RCTs. Another two investigators independently extracted data. The primary efficacy outcomes (composite of deep venous thrombosis, non-fatal pulmonary embolism and death of all causes) and the primary bleeding outcomes (major bleeding and non-major but clinically relevant bleeding) were summarized for meta-analysis. Stata software was used for traditional meta-analysis and dose-response meta-analysis, and Winbugs software was used for network meta-analysis.

RESULTS

Twenty trials with 38,507 subjects in the intention-to-treat population were included. Compared with enoxaparin, the risk of total venous thromboembolism was lower with rivaroxaban (relative risk 0.70, 95% confidence interval 0.60 to 0.81), apixaban (0.62, 0.47 to 0.81), and edoxaban (0.62, 0.39 to 0.97) and similar to darexaban (0.96, 0.84 to 1.11) and betrixaban (1.28, 0.97 to 1.68). Compared with enoxaparin, the risk of major or clinically relevant non-major bleeding was higher with rivaroxaban (1.52, 1.14 to 2.02), lower with betrixaban (0.34, 0.14 to 0.84) and similar to apixaban (0.88, 0.73 to 1.05), darexaban (0.85, 0.66 to 1.09) or edoxaban (1.30, 0.72 to 2.33). The risk of major and clinically relevant non-major bleeding of rivaroxaban had a linear relationship with its treatment doses; the risk of total venous thromboembolism of betrixaban and darexaban had linear relationships with their respective treatment doses. There was no linear nor non-liner relationships between the effect of apixaban and its treatment dose. The ranking of total venous thromboembolism risk from low to high was: rivaroxaban, apixaban, edoxaban, enoxaparin, darexaban, and betrixaban. The ranking of major and clinically relevant non-major bleeding from low to high was: betrixaban, enoxaparin, darexaban, edoxaban, apixaban, and rivaroxaban.

CONCLUSIONS

Direct oral factor Xa inhibitors are more effective to prevent venous thromboembolism after total hip or knee replacement. Their anticoagulant effect was not necessarily compromised with a higher bleeding risk. Rivaroxaban, apixaban and edoxaban showed a better anticoagulant effect, as compared with enoxaparin. Rivaroxaban had a higher bleeding rate, while apixaban and edoxaban did not show significantly higher bleeding risks.

Measurement of rivaroxaban and apixaban in serum samples of patients

BACKGROUND

The determination of rivaroxaban and apixaban from serum samples of patients may be beneficial in specific clinical situations when additional blood sampling for plasma and thus the determination of factor Xa activity is not feasible or results are not plausible.

MATERIALS AND METHODS

The primary aim of this study was to compare the concentrations of rivaroxaban and apixaban in serum with those measured in plasma. Secondary aims were the performance of three different chromogenic methods and concentrations in patients on treatment with rivaroxaban 10 mg od (n = 124) or 20 mg od (n = 94) or apixaban 5 mg bid (n = 52) measured at different time.

RESULTS

Concentrations of rivaroxaban and apixaban in serum were about 20-25% higher compared with plasma samples with a high correlation (r = 0·79775-0·94662) using all assays (all P < 0·0001). The intraclass correlation coefficients were about 0·90 for rivaroxaban and 0·55 for apixaban. Mean rivaroxaban concentrations were higher at 2 and 3 h compared with 1 and 12 h after administration measured from plasma and serum samples (all P-values < 0·05) and were not different between 1 vs. 12 h (plasma and serum).

CONCLUSIONS

The results indicate that rivaroxaban and apixaban concentrations can be determined specifically from serum samples.

Preventive strategies against bleeding due to nonvitamin K antagonist oral anticoagulants

Dabigatran etexilate (DE), rivaroxaban, and apixaban are nonvitamin K antagonist oral anticoagulants (NOACs) that have been compared in clinical trials with existing anticoagulants (warfarin and enoxaparin) in several indications for the prevention and treatment of thrombotic events. All NOACs presented bleeding events despite a careful selection and control of patients. Compared with warfarin, NOACs had a decreased risk of intracranial hemorrhage, and apixaban and DE (110 mg BID) had a decreased risk of major bleeding from any site. Rivaroxaban and DE showed an increased risk of major gastrointestinal bleeding compared with warfarin. Developing strategies to minimize the risk of bleeding is essential, as major bleedings are reported in clinical practice and specific antidotes are currently not available. In this paper, the following preventive approaches are reviewed: improvement of appropriate prescription, identification of modifiable bleeding risk factors, tailoring NOAC's dose, dealing with a missed dose as well as adhesion to switching, bridging and anesthetic procedures.

Clinical trials with new oral anticoagulants. Additive value of indirect comparisons also named network meta-analyses

To compare the efficacy and safety of the new oral anticoagulants (NOAC), ideally head-to-head clinical trials should be performed. Given the expense of such an undertaking, it is highly unlikely that such a comparison would be performed. Therefore, there is a need for an unbiased comparative assessment of the benefits and risks of the NOACs, based on the available trial data. Indirect or mixed treatment comparisons may be an useful tool to overcome these limitations also known as network meta-analysis (NMA). The aim of this paper is to give an overview on published NMAs for dabigatran, rivaroxaban and apixaban, each assessed against warfarin in patients with atrial fibrillation, and against enoxaparin in patients undergoing total knee and total hip replacement surgery, in order to obtain insights into the comparability of the adopted methodological techniques.