Abstract 14572: Poor Understanding and Compliance Among AF Patients on Warfarin Who Use Vitamin Supplements
Background: Vitamin supplements can interact with warfarin, exposing patients that use them to risk of thromboembolism and/or bleeding. It is unknown if patients that use vitamin supplements have more understanding of warfarin that may minimize the interaction risk.
Methods: A 52-item questionnaire related to knowledge of warfarin was administered in a face-to-face interview with a dietitian in 100 patients with atrial fibrillation on warfarin therapy. This study examines (1) general knowledge of warfarin therapy, (2) warfarin compliance, and (3) adverse outcomes associated with warfarin use in patients that use vitamins (n=62) compared to those who do not (n=37).
Results: Stroke risk factors included hypertension (57%), heart failure (36%), age >75 years (33%), diabetes (22%), and prior stroke/transient ischemic attack (29%). There were no significant differences in baseline demographics based upon vitamin use. Patients who took vitamins frequently skipped doses of warfarin (24% of patients) and, in comparison to those not using vitamins, more often doubled doses of warfarin (2% vs. 0%). Patients who took vitamins were less aware of potential vitamin-warfarin interactions (37% vs. 30%). As a consequence, more strokes occurred in patients who used vitamins (13% vs. 5%), and they experienced higher rates of unexplained bleeding/hematuria/blood in stool (23% vs. 19%) and nonoperative need for blood transfusions (13% vs. 8%).
Discussion: Atrial fibrillation patients that use vitamins are less compliant with warfarin and less aware of the potential risks of their supplement use overall. These patients had higher rates of bleeding and thromboembolism. Physicians must ask about vitamin use in warfarin patients and improve education to minimize bleeding risk and to maximize drug understanding and compliance.
- © 2011 by American Heart Association, Inc.