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 CHADS(2)
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.