The costs of warfarin underuse and nonadherence in patients with atrial fibrillation: a commercial insurer perspective.

BACKGROUND: Atrial fibrillation (AF) imposes a substantial clinical and economic burden on the U.S. health care system. Despite national guidelines that recommend oral anticoagulation for stroke prevention, the literature consistently reports its underuse in AF patients with moderate to high stroke risk.

OBJECTIVE: To assess the economic burden of underuse and nonadherence of warfarin therapy among patients with nonvalvular AF in a commercially insured population.

METHODS: Claims data between January 2003 and December 2007 from the Thomson Reuters MarketScan Research Database were used. Patients diagnosed with nonvalvular AF who were continuously enrolled for at least 12 months prior to and 2 months following their diagnosis, who had a CHADS₂ score ≥ 2, and were not at high risk of bleeding (ATRIA score less than 5, HEMORR₂HAGE score less than 4, and HAS-BLED score less than 3) at baseline were included. Patients were followed for up to 18 months after the AF diagnosis date to assess the level of warfarin utilization. Health care resource utilization and cost during follow-up among patients with the proportion of days covered (PDC) by warfarin greater than 0.8 (high) and ≤ 0.8 (low) versus patients with no warfarin exposure were assessed. Multivariate negative binomial regressions and generalized linear models were used to estimate differences in resource utilization and cost, respectively.

RESULTS: Of the 13,289 subjects included in this analysis, 47% had no warfarin exposure; 31.5% had low PDC; and 21.5% had high PDC. The rates of ischemic stroke and transient ischemic attack (per 100 patient-years) were significantly lower for the groups that had high and low PDCs as compared with the group with no warfarin exposure (P less than 0.001). Multivariate analysis showed that patients with high PDC were 27% less likely (P less than 0.001) to incur hospitalizations, and 16% were less likely (P = 0.019) to incur emergency room visits than patients who did not receive warfarin, but the differences between low PDC patients and no warfarin exposure were not significant. Although both low and high PDC were associated with lower all-cause inpatient cost (P less than 0.001), only high PDC was associated with a lower post-index all-cause total cost (P less than 0.001) compared with no warfarin exposure.

CONCLUSION: Our results confirm that underutilization and nonadherence of warfarin among nonvalvular AF patients is both prevalent and costly. Warfarin use among patients with moderate to high stroke risk and low to moderate bleed risk demonstrated a stroke benefit without a significant increase in intracranial hemorrhage. Adherence to oral anticoagulant therapy was associated with a significant reduction in inpatient service use and total health care cost. Improving adherence to oral anticoagulation is important to attaining the clinical and economic benefits of therapy.