When academic research organizations and clinical research organizations disagree: Processes to minimize discrepancies prior to unblinding of randomized trials

Current Opinion on the use of Direct Oral Anticoagulants for the Prophylaxis of Venous Thromboembolism among Medical Inpatients

Venous thromboembolism (VTE) is a known cause of morbidity and mortality, especially among acutely ill medical patients. Although VTE prophylaxis is part of post-discharge clinical care in surgical patients, there is controversy regarding its use in acutely ill medical patients and the current guideline statements suggest against its routine use. Recent clinical trials (APEX, MAGELLAN and MARINER) compared the safety and efficacy of direct oral anticoagulants (including betrixaban and rivaroxaban) with the standard of the care, enoxaparin, to identify the risk–benefit tradeoff. In this review, we summarized the key findings from these trials and substudies and recent updates in society guidelines regarding VTE prevention. In addition, we discussed the potential barriers, cost-effectiveness, and COVID-19 with respect to the implementation of extended-duration or post-discharge usage of direct oral anticoagulants.

Post-hospital discharge venous thromboembolism prophylaxis in medically ill patients

There is a widely expressed concern about an unmet need for post hospitalization venous thromboembolism (VTE) prophylaxis in medically ill patients, however, physicians and hospitals have been slow to implement this measure. Recommendations against extended VTE prophylaxis in medical patients from the American Society of Hematology (ASH) in 2018 and the withholding of approval of betrixiban by the European Medicines Agency also in 2018 may have been influential in this regard. Furthermore, rivaroxaban the other drug approved for this indication in the U.S has not yet been approved in Europe. In addition, hospital administrators, those monitoring expenses in the U.S, have been reluctant to support a treatment which will mostly involve outpatients. Internal medicine physicians, hospitalists and nursing home physicians have not shared the fervor for post hospital VTE prophylaxis, whether with anticoagulants or aspirin, that their orthopedic surgery colleagues have, particularly in hip and knee arthroplasty. This is despite an increased risk of post hospital discharge thrombosis in both groups of patients. Enter hospitalized patients with COVID-19, a potentially severe medical illness with high hospitalization related thrombosis risk, and questions arise as to whether these medical patients, who are clearly more hypercoagulable during hospitalization than those in previous studies, should warrant post hospital discharge prophylaxis.

Single-Study Approvals: Quantum of Evidence Required

When does a single positive adequate and well-controlled study of a new drug meet the statutory requirement to demonstrate substantial evidence of effectiveness? The answer to this question, particularly with respect to new molecular entities, has been of considerable debate since 1962 when the requirement that new drugs prove their benefit to patients became law. A 1997 revision to the statute provided one pathway to a single-study approval (a single adequate and well-controlled study plus confirmatory evidence), while a 1998 guidance issued by FDA provided additional pathways, one of which is the one that is most frequently cited by FDA (a single statistically very persuasive study). This paper explains these 2 distinct pathways and provides illustrative examples of how FDA uses each of these 2 pathways. Regulators, industry, patients, and investors should each find this exegesis of these 2 independent, yet equally viable and valuable, pathways to an FDA approval both illuminating and invaluable.

Betrixaban in the prevention of venous thromboembolism in medically ill patients

Despite significant advances in strategies and compliance with venous thromboembolism (VTE) prophylaxis, hospital-acquired VTE remains a leading cause of preventable deaths in acute medically ill patients. A majority of venous thromboembolic events occur posthospital discharge when risk factors persist and pharmacoprophylactic regimens have been completed. Until recently, there has been an unmet need for safe and effective extended-duration VTE prevention. Three major trials evaluated this concept, but excess bleeding outweighed the benefit of reduced thromboembolic events. Betrixaban is an oral direct factor Xa inhibitor recently approved for extended-duration VTE prophylaxis in acute medically ill patients at risk for thromboembolism based on results from the Phase III APEX study. This article reviews the pharmacology and supporting data for betrixaban.

Betrixaban for first-line venous thromboembolism prevention in acute medically ill patients with risk factors for venous thromboembolism

INTRODUCTION

Compared to other direct oral anticoagulants, betrixaban has a longer half-life, smaller peak-trough variance, minimal renal clearance, and minimal hepatic Cytochrome P (CYP) metabolism. The Acute Medically Ill VTE Prevention with Extended Duration Betrixaban (APEX) trial evaluated the efficacy and safety of extended duration betrixaban compared to standard duration enoxaparin in acutely ill hospitalized patients. Areas covered: This article describes the role of betrixaban in the prevention of venous thromboembolism (VTE) in acutely ill medical patients. This article provides a consolidated summary of the primary APEX study findings as well as prespecified and exploratory substudies. This article also provides a review of the results of studies in which other direct factor Xa inhibitors have been evaluated in an extended duration regimen in this patient population. Expert commentary: While previous agents have demonstrated that extended duration VTE prophylaxis can be efficacious, betrixaban is the first agent to demonstrate efficacy without an increase in major bleeding. The totality of the data from the APEX trial supports extended duration betrixaban for VTE prophylaxis in the acute medically ill patient population. As such, betrixaban has been approved in the USA for extended VTE prophylaxis in at-risk acute medically ill patients.

Betrixaban for prevention of venous thromboembolism in acute medically ill patients

Venous thromboembolism (VTE) is a common, potentially preventable cause of morbidity and mortality among acute medically ill patients. More than half of VTE events in this population occur after hospital discharge. Thus, providing extended-duration VTE prophylaxis from in-hospital through the post-discharge continuum may improve the quality of care in patients at risk of VTE. Betrixaban is a new oral, once-daily factor Xa inhibitor approved by the United States (US) Food and Drug Administration (FDA) for extended-duration prophylaxis of VTE in acute medically ill patients. The clinical efficacy and safety of betrixaban in acute medically ill patients perceived to be at high risk for VTE were evaluated in a large, randomized, double-blind, active-controlled, multinational clinical trial [Acute Medically Ill VTE Prevention With Extended Duration Betrixaban (APEX)]. Patients were randomized to receive subcutaneous enoxaparin (10 ± 4 days) or oral betrixaban (35–42 days) plus matching placebos. The primary efficacy outcome was a composite of asymptomatic proximal deep vein thrombosis and symptomatic VTE; the primary safety measure was major bleeding. Extended-duration betrixaban reduced VTE events without an increase in major bleeding in the modified intent-to-treat analysis. Post hoc analyses of the APEX trial provided further evidence to support the efficacy and safety of betrixaban in reducing all-cause ischaemic stroke, fatal or irreversible ischaemic or bleeding events, as well as reducing VTE-related rehospitalization. In summary, analyses of the APEX study demonstrated a positive benefit–risk profile for extended prophylaxis of VTE with betrixaban in acute medically ill patients. This is likely to have important public health and health economic implications.

Betrixaban: A New Oral Factor Xa Inhibitor for Extended Venous Thromboembolism Prophylaxis in High-Risk Hospitalized Patients

OBJECTIVE

To review the pharmacology, pharmacokinetics, efficacy, and safety of the factor Xa (FXa) inhibitor betrixaban for extended-duration prophylaxis of acute medically ill patients with venous thromboembolism (VTE) risk factors.

DATA SOURCES

A MEDLINE/PubMed (January 1990 to October 2017) search was conducted using the following keywords: betrixaban, PRT054021, FXa inhibitor, novel oral anticoagulant, NOAC, direct oral anticoagulant, DOAC, and target specific oral anticoagulant, TSOAC. References of identified articles were searched by hand for additional relevant citations.

STUDY SELECTION AND DATA EXTRACTION

We included English-language articles evaluating betrixaban pharmacology, pharmacokinetics, efficacy, or safety in human subjects for VTE prophylaxis.

DATA SYNTHESIS

Betrixaban is a FXa inhibitor that decreases prothrombinase activity and thrombin generation. Betrixaban efficacy and safety has been compared with that of enoxaparin for prophylaxis of VTE in acutely ill medical patients. In the APEX trial and substudies, extended-duration betrixaban was superior in efficacy to standard-duration enoxaparin in patients at high risk for VTE, including those with elevated D-dimer levels (≥2× upper limit of normal) and of older age (≥75 years). Betrixaban is noninferior to enoxaparin in rates of major bleeding, but the former is associated with more clinically relevant nonmajor bleeding events.

CONCLUSION

Betrixaban is the first oral agent approved for extended-duration VTE prophylaxis in acutely ill hospitalized patients. Extended-duration thromboprophylaxis with betrixaban reduces the risk of VTE compared with standard-duration thromboprophylaxis with enoxaparin but is associated with increased risk of bleeding.

Extended thromboprophylaxis in the acutely ill medical patient after hospitalization - a paradigm shift in post-discharge thromboprophylaxis

Venous thromboembolism (VTE) is a significant healthcare burden with approximately 900,000 events annually in the United States, over half of which are healthcare-associated. This number is anticipated to double by 2050. Group prophylaxis strategies confined to the inpatient setting appear to have minimal impact on the reduction of post-discharge VTE in medically ill patients due to shortened lengths of stay and a heterogenous population that includes patients at low risk for VTE. In accordance with current guideline recommendations, very few (<5%) medically ill patients are discharged with extended prophylaxis, which potentially creates a clinical gap for at-risk patients as VTE risk has been shown to persist for up to 90 days. Initial studies of extended thromboprophylaxis in acutely ill medical patients with enoxaparin, rivaroxaban and apixaban showed little to no benefit towards VTE reduction that was consistently outweighed by increased bleeding. The more recent APEX study that compared betrixaban to enoxaparin in an enriched patient population at high-risk for VTE was the first study of extended thromboprophylaxis that showed similar efficacy in VTE prevention without an increase in major bleeding. Based on the APEX results, betrixaban recently gained FDA approval for extended thromboprophylaxis in acutely ill medical patients. Recognition that up to half of medically ill patients are not at sufficient risk to warrant thromboprophylaxis has driven extensive research towards development of scientifically derived and validated VTE risk assessment models intended to identify patients who do not warrant prophylaxis, as well as those at high risk who may derive benefit from extended thromboprophylaxis. This article will review prior and ongoing extended thromboprophylaxis studies, VTE and bleed risk assessment models, incorporation of biomarkers in VTE risk assessment and key issues in the paradigm shift towards individualized VTE prophylaxis in acutely ill medical patients.