APEX

Background

Phase 3 double-blind RCT (APEX). 7,513 acutely ill medical patients with reduced mobility and elevated VTE risk, enriched for high-risk features (elevated D-dimer or age ≥75). Compared extended betrixaban prophylaxis (35–42 days) to standard enoxaparin prophylaxis (10 ± 4 days) followed by placebo. Betrixaban is an oral direct factor Xa inhibitor with unique once-daily dosing, minimal hepatic metabolism, and predominantly fecal excretion. APEX used adaptive enrichment strategy to identify patients most likely to benefit — learning from MAGELLAN's failure in unselected patients.

Interventions and follow up

Arm A: Betrixaban 80 mg once daily × 35–42 days (dose-reduced to 40 mg if CrCl 15–30 mL/min or P-gp inhibitor use)
Arm B: Enoxaparin 40 mg SC once daily × 10 ± 4 days, then oral placebo × 25–32 day
Primary endpoint: Composite of asymptomatic proximal DVT, symptomatic DVT, non-fatal PE, or VTE-related death — tested hierarchically: cohort 1 (elevated D-dimer) → cohort 2 (cohort 1 + age ≥75) → cohort 3 (all patients)
mFollow up: 77 day

Results

VTE composite (cohort 1, elevated D-dimer): 6.9% vs 8.5%; RR 0.81, 95% CI 0.65–1.00 — P=.054 (did not cross significance threshold)
VTE composite (cohort 2, D-dimer + age ≥75): 5.6% vs 7.1%; RR 0.80, 95% CI 0.66–0.98 — P=.03
VTE composite (all patients): 5.3% vs 7.0%; RR 0.76, 95% CI 0.63–0.92 — P=.006
Major bleeding (all patients): 0.7% vs 0.6%; RR 1.19, 95% CI 0.67–2.12 — P=.55

Adverse events

Main adverse events: Major bleeding not significantly different (0.7% vs 0.6%; P=.55). Clinically relevant non-major bleeding: 2.7% vs 2.2% (non-significant). Fatal bleeding: 0.1% each arm. No significant hepatotoxicity. Betrixaban showed a more favorable bleeding profile than rivaroxaban in MAGELLAN, possibly due to different pharmacokinetics (less renal excretion, fecal predominant).

Conclusions

Betrixaban extended prophylaxis reduced VTE in enriched high-risk medical patients without significantly increasing major bleeding, meeting the pre-specified threshold only in cohort 2 (per hierarchical testing); the overall patient population showed benefit, but the primary statistical test (cohort 1) was borderline (P=.054).

Key Limitations

Key Limitations: The pre-specified hierarchical testing strategy failed at the primary endpoint (cohort 1, P=.054) — statistical success was only in the broader population as an exploratory analysis. FDA reviewers noted the primary endpoint was not formally met. Asymptomatic DVT (compression ultrasound) drives much of the composite — clinical significance debated. Betrixaban is no longer marketed in the US (withdrawn 2019 by Portola, later acquired by Pfizer, discontinued commercially). The enrichment strategy was exploratory.

Clinical Context

APEX led to FDA approval of betrixaban for VTE prophylaxis in acutely ill medical patients in June 2017 — the first DOAC approved for extended medical prophylaxis. However, betrixaban was withdrawn from the US market in 2019 due to commercial reasons. MARINER trial (rivaroxaban 10 mg) followed with a similar enrichment approach. Extended pharmacological prophylaxis for medical inpatients remains controversial — current guidelines recommend using validated risk stratification tools (IMPROVE VTE + IMPROVE Bleed scores) to select appropriate patients.

References

References: Cohen AT et al, NEJM 2016 (APEX); PMID 26999202