Design: Phase 3, randomised, placebo-controlled, stopped at interim for futility (LIBREXIA-ACS)
Population: 14,194 patients within 7 days of an acute coronary syndrome, on antiplatelet therapy
Primary outcome: Cardiovascular death, MI or ischaemic stroke
Effect: 5.4% vs 5.1%, HR 1.05 (95% CI 0.91–1.21); critical bleeding 0.3% vs 0.3%

LIBREXIA-ACS was a phase 3, placebo-controlled trial of milvexian, an oral factor XIa inhibitor, 25 mg twice daily, added to standard antiplatelet therapy within 7 days of an acute coronary syndrome. It was stopped for futility at a planned interim analysis after 14,194 patients had been enrolled.

Over a median 12.2 months, cardiovascular death, MI or ischaemic stroke occurred in 5.4% on milvexian and 5.1% on placebo (HR 1.05, 95% CI 0.91–1.21). Intracranial, vision-threatening intraocular or fatal bleeding was 0.3% in both groups.

The class's promise was that factor XI inhibition could prevent thrombosis without the bleeding cost of conventional anticoagulants. In coronary disease, on top of antiplatelet therapy, this trial found the bleeding safety but no efficacy. It does not answer the question for AF or stroke prevention, where the class is being tested separately and the thrombotic mechanism differs.

No role for factor XIa inhibitors after ACS on current evidence.
Keep post-ACS antithrombotic therapy to guideline antiplatelet regimens.
The bleeding result supports continued study of the class in atrial fibrillation and stroke, which are separate questions.
Milvexian is not approved anywhere; patients asking about 'safer blood thinners' after MI should be told the trial was negative.

Why it matters

Low bleeding alone is not enough — this is the first large test of factor XI inhibition in coronary disease and it found no efficacy.

The statistics, in plain English

An HR of 1.05 with a confidence interval from 0.91 to 1.21 means the trial effectively excluded any benefit larger than about a 9% relative reduction — which is why it stopped early for futility.