December 19th, 2013
Early Doses of Warfarin Paradoxically Associated with Higher Stroke Risk
Patients with atrial fibrillation seem to be at increased risk for ischemic stroke when starting warfarin prophylaxis, according to a case-control study in the European Heart Journal.
The study was undertaken after trials of both apixaban and rivaroxaban noted increased stroke risks among patients transitioning to open-label warfarin. This study was funded by the makers of apixaban.
Using a U.K. database, researchers examined a cohort of some 70,000 patients with AF; they matched 5500 cases of ischemic stroke with 55,000 controls. AF patients initiating warfarin therapy had a 71% increased risk for ischemic stroke within the first 30 days of therapy, compared with those on no anticoagulants. The risk was highest in the first week. However, the warfarin group had half the stroke risk after 30 days.
The authors say the observed “paradoxical procoagulant effect” may be due to warfarin’s effect in blocking some endogenous anticoagulants.