The New England Journal of Medicine NOVEMBER 28, 2013

Edoxaban versus Warfarin in Patients with Atrial Fibrillation

Robert P. Giugliano, Christian T. Ruff, Eugene Braunwald, et al. for the ENGAGE AF-TIMI 48 Investigators

Bottom Line

In patients with nonvalvular atrial fibrillation, once-daily edoxaban (at high and low doses) was noninferior to well-managed warfarin for the prevention of stroke or systemic embolism and was associated with significantly lower rates of major bleeding and cardiovascular mortality.

Key Findings

1. High-dose edoxaban (60 mg) was noninferior to warfarin for the primary efficacy endpoint of stroke or systemic embolic event (SEE), with an annualized rate of 1.18% versus 1.50% (Hazard Ratio 0.79; 97.5% CI, 0.63 to 0.99; P<0.001 for noninferiority).

2. Both high-dose and low-dose edoxaban regimens were associated with significantly lower rates of major bleeding compared to warfarin (2.75% and 1.61% per year, respectively, versus 3.43% for warfarin; P<0.001 for both).

3. Cardiovascular mortality was significantly lower in both the high-dose edoxaban group (2.74%/year) and the low-dose edoxaban group (2.71%/year) compared to the warfarin group (3.17%/year; P=0.01 and P=0.008, respectively).

4. Despite the reduction in major bleeding, high-dose edoxaban was associated with a higher incidence of gastrointestinal bleeding compared to warfarin.

Study Design

Design

RCT

Double-Blind, Double-Dummy

Sample

21,105

Patients

Duration

2.8 yr

Median

Setting

Multicenter, Global

Population Patients with documented nonvalvular atrial fibrillation and a moderate-to-high risk of stroke (CHADS2 score >= 2).

Intervention Once-daily edoxaban at high-dose (60 mg) or low-dose (30 mg) regimens (with prespecified dose reduction to 30 mg or 15 mg respectively based on clinical criteria).

Comparator Warfarin, adjusted to an INR of 2.0 to 3.0.

Outcome Composite of stroke or systemic embolic event (SEE).

Study Limitations

• The primary analysis was performed on an on-treatment modified intention-to-treat population, which may differ from a pure intention-to-treat analysis.

• The low-dose edoxaban arm, while reducing bleeding, was associated with an increased risk of ischemic stroke compared to the high-dose arm and warfarin.

• The trial utilized a dose-reduction strategy based on clinical factors (creatinine clearance, body weight, P-glycoprotein inhibitor use), which complicates direct comparisons to anticoagulants that do not require such adjustments.

• The observed efficacy of edoxaban in patients with high creatinine clearance (>95 mL/min) was lower than in those with more reduced renal function.

Clinical Significance

The trial established edoxaban as a viable once-daily oral alternative to warfarin for stroke prevention in nonvalvular atrial fibrillation, particularly emphasizing its safety profile with reduced rates of intracranial hemorrhage and cardiovascular mortality. Its efficacy relative to warfarin, even with high-quality INR control (TTR 68.4%), supports its role as a major direct oral anticoagulant (DOAC) option.

Historical Context

The ENGAGE AF-TIMI 48 trial was the final landmark Phase 3 trial of the initial wave of direct factor Xa inhibitors (following RE-LY for dabigatran, ROCKET AF for rivaroxaban, and ARISTOTLE for apixaban). It is distinguished by being the largest and longest trial in the class at the time of publication and featured a unique two-dose regimen to accommodate patients with specific risk factors for bleeding.

Guided Discussion

High-yield insights from every perspective

Med Student

Medical Student

How does the mechanism of action of edoxaban differ from that of warfarin, and how does this explain its lower rate of intracranial hemorrhage observed in the ENGAGE AF-TIMI 48 trial?

Key Response

Edoxaban is a direct, reversible inhibitor of Factor Xa, blocking the common pathway of coagulation. In contrast, warfarin inhibits Vitamin K epoxide reductase, affecting the synthesis of Factors II, VII, IX, and X, as well as proteins C and S. The higher specificity of direct oral anticoagulants (DOACs) like edoxaban and their lack of interference with the 'extrinsic' pathway (specifically Factor VII, which has a short half-life and plays a crucial role in initial hemostasis) is thought to contribute to the significantly lower risk of intracranial hemorrhage compared to the broad inhibition seen with Vitamin K antagonists.

Resident

When considering the results of ENGAGE AF-TIMI 48, which patient populations would benefit most from the low-dose (30/15 mg) edoxaban regimen despite the trend toward higher ischemic stroke rates?

Key Response

The low-dose edoxaban regimen showed a significantly lower rate of major bleeding and cardiovascular mortality compared to warfarin, but it did not meet the primary noninferiority endpoint as robustly as the high-dose regimen for ischemic stroke prevention. Residents should identify that the low-dose regimen might be considered for patients at exceptionally high risk for bleeding where anticoagulation is still necessary, though the high-dose (60/30 mg) remains the standard of care for optimal stroke prevention in most AF patients.

Fellow

The ENGAGE AF-TIMI 48 trial revealed a unique interaction between edoxaban efficacy and renal function. How should a clinician manage a patient with a creatinine clearance (CrCl) > 95 mL/min who is being considered for edoxaban?

Key Response

Subgroup analyses and subsequent FDA labeling highlight that edoxaban (60 mg) is less effective than warfarin in patients with a CrCl > 95 mL/min. This is likely due to increased renal clearance of the drug leading to lower plasma concentrations. Fellows must recognize that for patients with 'supranormal' renal function, alternative DOACs like apixaban or rivaroxaban, or even warfarin, should be prioritized to ensure adequate stroke prophylaxis.

Attending

The ENGAGE AF-TIMI 48 trial showed a significant reduction in cardiovascular mortality with edoxaban compared to warfarin. How does this finding influence the 'Net Clinical Benefit' discussion when counseling a patient with a high CHA2DS2-VASc score and a high HAS-BLED score?

Key Response

The reduction in cardiovascular death (likely driven by fewer fatal bleeds and intracranial hemorrhages) suggests that edoxaban provides a superior safety profile that translates into a survival benefit. When counseling high-risk patients, the 'Net Clinical Benefit' shifts toward edoxaban over warfarin because it maintains noninferiority in stroke prevention while providing a wider safety margin against the most catastrophic complications of anticoagulation.

Scholarly Review

Critical appraisal through the lens of expert reviewers and guideline development

PhD

Critique the use of the 'Modified Intention-to-Treat' (mITT) analysis for the primary noninferiority endpoint in ENGAGE AF-TIMI 48. Why is this statistical approach preferred over a standard ITT in noninferiority trials?

Key Response

In noninferiority trials, a standard ITT analysis can be conservative because it tends to dilute treatment differences, potentially making a truly inferior drug appear noninferior (moving the result toward the null). The mITT (including patients who received at least one dose and while on study drug) is more sensitive to the actual pharmacologic effects of the treatment, thereby providing a more rigorous test of the noninferiority hypothesis by minimizing the 'noise' of non-compliant patients.

Journal Editor

A major threat to the internal validity of DOAC trials is the quality of warfarin management in the control arm. How did the Time in Therapeutic Range (TTR) in ENGAGE AF-TIMI 48 affect the study's generalizability, and what would a reviewer flag regarding the 'center-average TTR'?

Key Response

The median TTR in the warfarin arm was 68.4%, which is considered high quality. However, a tough reviewer would examine the variability in TTR across different global sites. If edoxaban's benefit were only seen in centers with poor TTR (e.g., <60%), the claim of superiority in safety might be challenged. The trial's robustness stems from the fact that edoxaban's benefits were largely consistent across various levels of site-based TTR, reinforcing its real-world applicability.

Guideline Committee

Given the findings of ENGAGE AF-TIMI 48, should clinical guidelines provide a Class I recommendation for edoxaban in all nonvalvular AF patients, or should there be specific exclusions based on renal function?

Key Response

Current AHA/ACC/HRS guidelines generally recommend DOACs (including edoxaban) over warfarin (Class I, Level A). However, the committee must specify the 'Edoxaban Paradox'—the FDA boxed warning and guideline notation that edoxaban should not be used in patients with CrCl > 95 mL/min. This demonstrates that while the trial supports edoxaban as a first-line agent, the evidence base requires a nuanced, individualized approach to dosing and selection based on renal clearance that is not required for all other DOACs.

Clinical Landscape

Noteworthy Related Trials

2009

RE-LY Trial

n = 18,113 · NEJM

Tested

Dabigatran (110mg or 150mg twice daily)

Population

Patients with atrial fibrillation and risk of stroke

Comparator

Warfarin

Endpoint

Stroke or systemic embolism

Key result: Dabigatran 150 mg was superior to warfarin in preventing stroke or systemic embolism with similar rates of major hemorrhage.

2011

ROCKET-AF Trial

n = 14,264 · NEJM

Tested

Rivaroxaban 20mg daily

Population

Patients with nonvalvular atrial fibrillation at increased risk for stroke

Comparator

Warfarin

Endpoint

Stroke or systemic embolism

Key result: Rivaroxaban was non-inferior to warfarin for the prevention of stroke or systemic embolism in patients with nonvalvular atrial fibrillation.

2011

ARISTOTLE Trial

n = 18,201 · NEJM

Tested

Apixaban 5mg twice daily

Population

Patients with atrial fibrillation and at least one additional risk factor for stroke

Comparator

Warfarin

Endpoint

Stroke or systemic embolism

Key result: Apixaban was superior to warfarin in preventing stroke or systemic embolism, caused less bleeding, and resulted in lower mortality.

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