March 13, 2014
Inadequate warfarin therapy puts atrial fibrillation patients at increased risk of stroke and major hemorrhage, and may cause them to take costlier but easier-to-manage novel anticoagulants, suggested new research.
Warfarin is more effective if patients spend a greater percentage of time in therapeutic range, but the drug has a variable dose-response relationship and narrow therapeutic window that require frequent monitoring to maximize its anticoagulant effect, noted the study.
To assess the true difficulty in managing warfarin therapy, investigators accessed the database of Quest Diagnosis laboratories to review more than 138,319 AF patients who underwent INR testing by nearly 38,000 physicians between January 2007 and December 2008. According to their findings, only half of the nearly 2.7 million test results were in therapeutic range: 16.9% were too high (>3.0) and 32.5% were too low (<2.0).
The researchers noted the duration of warfarin exposure in the study was the most statistically significant factor associated with TTR: 47.6% for patients with fewer than 6 months of INR data versus 57.5% for those with more than 6 months of data. The mean overall TTR was 53.7% in labs across most of the country, below the 58% to 65% threshold needed for warfarin to achieve better efficacy than dual antiplatelet therapy.
Additionally, TTR for patients younger than 45 years was 45.5% compared with 53.9% for patients older than 75 years. Regardless of age, women had lower TTR and higher frequency of INR testing than men. Notably, nearly 95% of the physicians ordered warfarin testing on fewer than 10 patients, which suggests physician experience with anticoagulation therapy impacts warfarin’s effectiveness.
According to the researchers, their TTR results were lower than the mean center-based TTR values reported from recent randomized trials comparing novel oral anticoagulants with warfarin: dabigatran (64%), rivaroxaban (55%), and apixaban (62%).
“Healthcare institutions and patients are increasingly seeking avenues to reduce their medical costs without sacrificing quality or favorable outcomes,” said study co-author Dr. Elaine Hylek, a professor at the Boston University School of Medicine. “While warfarin may be a highly suitable therapy for many patients, the widespread suboptimal anticoagulation control reflected in our findings suggests some patients may be more appropriately treated with newer oral anticoagulants.”
The study was published online in the journal Circulation.
1. Dlott JS, George RA, Huang X, et al. A national assessment of warfarin anticoagulation therapy for stroke prevention in atrial fibrillation. Circulation. 2014 Feb 3. [Epub ahead of print]