Underutilization of Warfarin and Associated Costs

Cincinnati—Atrial fibrillation (AF), affecting approximately 2.3 million people in the United States, imposes a substantial clinical and economic burden and is associated with at least a 2-fold increase in the risk of stroke and stroke-related death. Anticoagulation is recommended for patients with AF who are at moderate or high risk for stroke, but who are not at high risk for bleeding.

According to researchers, warfarin is “often underprescribed and long-term adherence with warfarin is challenging, even among patients who were prescribed warfarin therapy.” Noting that there are limited data on ways underutilization of warfarin and low adherence rates may affect healthcare costs and outcomes, the researchers designed a study to examine the cost and consequences of warfarin underuse and nonadherence. Commercially insured patients with nonvalvular AF at moderate to high risk for stroke were included in the study.

The retrospective cohort analysis utilized the Thomson Reuters MarketScan^® database from January 1, 2003, to December 31, 2007. The database included Medicare beneficiaries with secondary commercial insurance. Inclusion criteria included being ≥18 years of age and having ≥2 AF diagnoses separated by at least 30 days, but by no more than 12 months. Patients included in the study had to have continuous enrollment in the health plan for 12 months prior to the initial AF diagnosis and ≥2 months of continuous eligibility following the initial AF diagnosis. Exclusion criteria were valvular or transient AF, CHADS₂ (congestive heart failure, hypertension, age ≥75 years, diabetes, stroke, transient ischemic attack [doubled]) score <12, prior warfarin use or contraindications to warfarin use, or being at high risk for bleeding.

The primary outcome measure was thromboembolic and bleeding events based on International Classification of Diseases, Ninth Revision, Clinical Modification, primary or secondary diagnosis codes in medical claims during the postindex period; major bleeding events were events that required hospitalization, identified by inpatient claims. The index date was the date of the initial diagnosis of nonvalvular AF.

Other outcome measures were all-cause patient hospitalizations (number of admissions and length of stays), emergency department visits, outpatient visits, stroke- and bleeding-related hospitalizations and outpatient visits, and their associated costs during the postindex period. Cost variables were expressed as per member per month (PMPM).

Following application of inclusion and exclusion criteria, 13,289 patients were included in the study. Of those, 52.94% (n=7036) received warfarin during the 18 months following the index date.

Compared with those who did not receive warfarin, patients in the warfarin group had significantly lower rates of ischemic stroke (4.41 vs 1.77; P<.001) and transient ischemic attack (1.77 vs 0.61; P<.001), and higher rates of major gastrointestinal bleeding (1.14 vs 1.87; P<.01) per 100 person-years. Rates of intracranial (0.54 vs 0.61) and other bleeding events (0.22 vs 0.28) per 100 person-years were similar between the 2 groups.

Compared with those who did not receive warfarin, those with low proportion of days covered (PDC) had a similar likelihood of inpatient and ED service utilization; however, they were 21% more likely to incur an outpatient visit during follow-up (P<.001). Patients with high PDC were 28% less likely to incur hospitalization (P<.001) and 16% less likely to incur ED visits (P<.05), but 23% more likely to incur outpatient visits (P<.001) compared with patients who did not receive warfarin.

Overall, total costs were 13% lower for patients with high PDC (P<.001), but similar for patients with low PDC compared with patients who did not receive warfarin.

In conclusion, the researchers noted that in this study, “warfarin provided a stroke benefit without a significant increase in the frequency of intracranial bleeds. A high warfarin PDC (>0.8) resulted in reductions in cost and resource utilizations compared with no warfarin exposure.” They commented that, “these findings support guideline recommendations for thromboprophylaxis and efforts to ensure adherence in this specific group of patients.”

This study was supported by Daiichi Sankyo Company, Limited.