MedWire News: Physicians may improve the quality of anticoagulation treatment by altering their warfarin dose management strategy, say US researchers who recommend tolerating small deviations from target international normalized ratio (INR).
“Our simulation suggests that, when the target [INR] range is 2.0–3.0, optimal management of warfarin would be to change the warfarin dose only when the INR is 1.7 or lower/3.3 or higher,” say Adam Rose (Bedford Veterans Affairs Medical Center, Massachusetts) and co-authors.
“A smaller tolerance for slightly out-of-range values seems to destabilize the INR through excessive dose adjustments.”
Recognizing that even carefully managed trial patients only spend around two-thirds of their time within their target therapeutic INR range (TTR), the team investigated the impact of altering warfarin dose on quality of anticoagulation.
Rose et al used data for 3961 warfarin users over 15.2 months to develop and validate a model to predict whether a physician would alter a warfarin dose under various clinical conditions. They computed an observed minus expected score for the number of changes predicted by their model versus the number of actual changes observed.
As reported in the Journal of Thrombosis and Haemostasis, patients who deviated the least from the predicted number of dose changes had the best INR control, with a mean TTR of 70.1%.
In contrast, patients who had significantly fewer or more dose alterations than expected had significantly poorer TTRs, at 65.8% and 62.0%, respectively.
Rose et al note that, on average, physicians changed warfarin dose when patients had an INR of ≤1.8 or ≥3.2, whereas optimal management would be to use INR thresholds of ≤1.7 and ≥3.3, respectively. These two strategies were predicted to give TTRs of 69% and 74%, respectively.
“Although our study may suggest an optimal dose management strategy in the absence of computerized decision support, definitive evidence would require prospective, randomized studies,” the researchers note.
“We would urge that such a trial be undertaken as soon as possible, as our study suggests that improving the dosing of warfarin could meaningfully improve patient outcomes.”
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