A Cohort Study of Warfarin Administered to Achieve An INR of 2.0 to 3.0 for the Prevention of Recurrent Venous Thrombosis in Patients with An Antiphospholipid Antibody.

Despite recent evidence, controversy remains regarding the optimal method of recurrent thrombosis prevention in patients with antiphospholipid antibodies (APLA) and prior thrombosis. Specifically, although two randomized trials have supported the efficacy of “usual intensity warfarin” (administered to a target INR of 2.0 to 3.0) there remains a dearth of prospective data examining this treatment.

The aim of our study was to confirm that patients with prior thrombosis and an APLA had a low risk of recurrent thrombosis while being treated with warfarin administered to achieve an INR of 2.0 to 3.0.

We examined the annual rate of recurrent thrombosis in patients with prior thrombosis and APLA who had all been treated with OAT (oral anticoagulant therapy) to achieve a target INR of 2.0 to 3.0.

Eligible patients had to have had at least one prior objectively confirmed arterial or venous thrombosis and at least one positive standardized test for an APLA. Patients were selected from the Victoria Hospital, and follow up appointments were conducted through the hospital's thrombosis clinic. Consenting patients underwent a baseline clinical examination with the intent to be followed every six months for evidence of recurrent thrombosis, adverse consequences of anticoagulation therapy, or until death.

Eighty three patients (mean age 50.5 years; 50 females) were enrolled; one patient was lost to follow up and did not contribute data to the analyses. Median follow up was 12 months (Range 5-18 months). No patients experienced a recurrent thrombotic event. 10 patients (12.2%) had a minor bleeding event (5 had significant ecchymosis, two had rectal bleeding, two had vaginal bleeding, and one had hematuria). No major bleeding events occurred. One patient had a presumed transient ischemic attack (TIA). One patient (1.2%) died during follow up due to multi-system organ failure in the context of a failing hepatic allograft.

Patients with previous thrombosis and an APLA have a low risk of recurrent thrombosis while having a target INR of 2.0 to 3.0. “Usual intensity warfarin” therapy appears to be an adequate method of thromboprophylaxis in these patients.

Crowther:BI: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bayer: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Honoraria, Research Funding; Leo Pharma: Consultancy, Honoraria, Research Funding; Sanofi-Aventis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Artisan Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees.