Category: Federal Forum Posters
Purpose: Direct oral anticoagulants (DOACs) are increasingly being prescribed for management of atrial fibrillation and venous thromboembolism. In accordance with this observation, both atrial fibrillation and venous thromboembolism CHEST guidelines recommend initiating DOACs over warfarin in certain populations. The purpose of this medication use evaluation was to evaluate and characterize patients currently receiving warfarin therapy for eligibility to DOAC conversion.
Methods: Patients were included for analysis if they had an active prescription for warfarin issued prior to January 1, 2018 and had received at least 6 international normalized ratio (INR) tests between October 16, 2017 and July 16, 2018. This time-frame was selected in order to capture established warfarin patients and ensure sufficient data to calculate a time in therapeutic range (TTR). Exclusion criteria included presence of any mechanical valve.
In total, 968 patients had an active warfarin prescription, of which a random sample of 48 patients were analyzed for inclusion. Of these, 15 patients met exclusion criteria (13 patients had a mechanical valve, 2 patients had fewer than 6 INR tests), leaving 33 patients for final analysis. The primary outcome was DOAC conversion eligibility. Secondary measures included TTR (calculated via the Rosendaal method), CHA2DS2-VASc score, HAS-BLED score, and adherence measured by proportion of days covered (PDC). Safety endpoints included any major or minor bleeding. Major bleeding included bleeding leading to death, transfusion of two or more units of blood, hospitalization, drop in hemoglobin by two or more units, or bleeding into a critical area or organ. Minor bleeding was defined as any bleed without definable cause.
Results: Nineteen (57.6%) patients were anticoagulated with warfarin for atrial fibrillation and 14 (42.4%) patients for venous thromboembolism. Of the 33 patients analyzed, 14 (42.4%) patients were ineligible for conversion to a DOAC. Reasons for ineligibility included weight greater than 120kg or BMI >40 (5 patients), mitral valve stenosis (1 patient), cirrhosis (1 patient), missing liver function tests (5 patients), and drug-drug interactions (2 patients). Mean PDC and TTR was 80.3% and 76.6%, respectively. Mean INR for the most recent test was 2.4 with a range of 1.7 – 3.4 over the study period. In the 19 atrial fibrillation patients, the median CHA2DS2-VASc and HAS-BLED scores were 5 and 1, respectively. Six bleeding events (1 major, 5 minor) occurred in 4 (12%) patients during the review timeframe.
Conclusion: Nearly 60% of evaluated patients were eligible for DOAC conversion. Of the 14 patients ineligible for conversion, 5 (35.7%) were ineligible due to missing liver function tests and may be eligible following laboratory testing. Warfarin patients included in this evaluation demonstrated high TTR, indicating excellent warfarin management and consistent anticoagulation. CHA2DS2-VASc and HAS-BLED scores demonstrate the risk of stroke is greater than bleeding risk in the evaluation sample. Bleeding was uncommon with only 4 (12%) patients experiencing a bleeding event.
John Sellers– Pharm.D. Candidate, University of Arizona College of Pharmacy, Litchfield Park, AZ