Warfarin sensitivity falls after valve surgery
MedWire News: Research indicates that a decrease in sensitivity to warfarin in the months after heart valve surgery may place patients at risk for receiving subtherapeutic anticoagulant therapy.
“Our findings are clinically important, as patients are at the highest risk of thromboembolic complications in the first months after surgery,” comment K Meijer (HHS-General Hospital, Hamilton, Ontario, Canada) and co-authors.
The team investigated whether their clinical impression that patients show a progressive decrease in warfarin sensitivity following cardiac surgery was supported by objective International Normalized Ratio (INR) data.
The researchers retrospectively examined warfarin dosing and INR results for 200 patients taking warfarin with a target INR of 2.0–3.0 in the first 3 months after receiving a mechanical or bioprosthetic valve or valve repair. They compared these results with findings from a group of patients receiving warfarin for atrial fibrillation (AF).
Analysis showed that in the 3 months after valve surgery, warfarin dose increased by an average of 26% and the average INR fell from 2.5 to 2.1 in the participants. Indeed, time in therapeutic range was just 48.5% in the patients and patients had an INR below 2.0 for 40.8% of the time.
In contrast, patients given warfarin for AF had steady doses of warfarin and INR values over 3 months of treatment.
“The most important practical conclusions from our data modeling are that dosing in these patients during the first 3 months must differ from our current practice and from widely used algorithms or nomograms in two ways,” Meijer et al say.
They suggest that warfarin dose increments should be increased in patients with an INR below the therapeutic range. In addition, the team recommends that warfarin dose should be increased in patients with an INR in the lower half of the therapeutic range.
Meijer et al say they have developed a dosing algorithm taking into account their findings and now plan to validate this in a prospective study.
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By Lynda Williams