Warfarin discontinuation after starting warfarin for atrial fibrillation

Abstract

Background: Although warfarin is widely recommended to prevent atrial fibrillation-related thromboembolism, many eligible patients do not take warfarin. The objective of this study was to describe factors associated with warfarin discontinuation in patients newly starting warfarin for atrial fibrillation. Methods and Results: We identified 4188 subjects newly starting warfarin in the Anticoagulation and Risk Factors in Atrial Fibrillation Study and tracked longitudinal warfarin use through pharmacy and laboratory databases. Data on patient characteristics, international normalized ratio (INR) tests, and incident hospitalizations for hemorrhage were obtained from clinical and laboratory databases. Multivariable Cox regression analysis was used to identify independent predictors of prolonged warfarin discontinuation, defined as ≥180 consecutive days off warfarin. Within 1 year after warfarin initiation, 26.3% of subjects discontinued therapy despite few hospitalizations for hemorrhage (2.3% of patients). The risk of discontinuation was higher in patients aged <65 years (adjusted hazard ratio [HR], 1.33 [95% CI, 1.03 to 1.72] compared to those aged ≥85 years), patients with poorer anticoagulation control (HR, 1.46 [95% CI, 1.42 to 1.49] for every 10% decrease in time in therapeutic INR range), and patients with lower stroke risk (HR, 2.54 [95% CI, 1.86 to 3.47] for CHADS2 stroke risk index of 0 compared to 4 to 6). Conclusions: More than 1 in 4 patients newly starting warfarin for atrial fibrillation discontinued therapy in the first year despite a low overall hemorrhage rate. Individuals deriving potentially less benefit from warfarin, including those with younger age, fewer stroke risk factors, and poorer INR control, were less likely to remain on warfarin. Maximizing the benefits of anticoagulation for atrial fibrillation depends on determining which patients are most appropriately initiated and maintained on therapy. © 2010 American Heart Association, Inc.