Six months of stable international normalized ratio values [INRs] while on warfarin therapy doesn’t predict continued INR stability, according to a Research Letter to the Editor published August 9 in JAMA.
Whether or not to switch patients with atrial fibrillation from warfarin to non–vitamin K anticoagulants remains controversial. “A common belief has been that patients with stable INRs while taking warfarin would continue to be stable and derive less benefit from switching to non–vitamin K oral anticoagulants,” said Sean D. Pokorney, MD, of the division of cardiology, Duke University Medical Center, Durham, N.C., and his associates.
But the results of their observational study of 3,749 patients enrolled in an atrial fibrillation registry show that such stability cannot be predicted, and “challenge the notion that patients who have done well taking warfarin should maintain taking warfarin,” the investigators said (JAMA. 2016;316:661-3).
They assessed INRs over the course of 3 years of follow-up using data from patients enrolled in the registry through 176 clinics. INR stability was defined as having 80% or more of INRs in the therapeutic range (2-3). The mean patient age was 75 years, and 43% were women.
A total of 968 patients showed such INR stability throughout the first 6 months of the study. However, 36% of them went on to have at least one “well out of range” INR during the following year. Even in the subgroup of 376 patients who had 100% of their INRs within the therapeutic range during the first 6 months, 33% went on to have at least one “well out of range” INR during the following year, according to Dr. Pokorney and his associates.
No sponsor was cited for this study. Dr. Pokorney reported ties to AstraZeneca, Boston Scientific, Gilead, Janssen, and Medtronic; his associates reported ties to numerous industry sources.