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Safety of Surgery during Bridging Anticoagulation Therapy with Low-Molecular-Weight Heparin FREE

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The summary below is from the full report titled “Brief Communication: Preoperative Anticoagulant Activity after Bridging Low-Molecular-Weight Heparin for Temporary Interruption of Warfarin.” It is in the 6 February 2007 issue of Annals of Internal Medicine (volume 146, pages 184-187). The authors are M.J. O'Donnell, C. Kearon, J. Johnson, M. Robinson, M. Zondag, I. Turpie, and A.G. Turpie.

Ann Intern Med. 2007;146(3):I-35. doi:10.7326/0003-4819-146-3-200702060-00002
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What is the problem and what is known about it so far?

Doctors commonly give blood thinners (anticoagulants) to patients who are at risk for the formation of blood clots that can result from many medical conditions. Warfarin, a pill that is taken by mouth, is commonly used for its anticoagulant effect. Warfarin is both effective and convenient to take, but it requires a few days to achieve adequate anticoagulation after the first dose and its effect on blood clotting lasts for 3 to 5 days after patients have stopped taking it. When a patient taking warfarin must undergo surgery, doctors have to stop warfarin treatment about 5 days before the procedure because anticoagulation can cause excessive bleeding, especially when tissues are cut. On the other hand, when the patient is not protected by anticoagulation, the risk for a dangerous blood clot increases. Doctors often handle this dilemma by stopping warfarin treatment several days before surgery and substituting a drug from a class of anticoagulants known as low-molecular-weight heparin. One member of this class is enoxaparin, a medication that must be given by injection, either once or twice daily. Enoxaparin treatment also must be stopped shortly before surgery, but because its effect does not last as long as that of warfarin, it can be stopped a shorter time before surgery. Common practice is to give the last dose of twice-daily enoxaparin the evening before surgery. Once surgery is finished, enoxaparin treatment is restarted until warfarin therapy is resumed adequately. Using enoxaparin this way is known as “bridging” therapy.

Why did the researchers do this particular study?

To find out whether the anticoagulant effect of enoxaparin goes away when the last dose is given the evening before surgery (more than 12 hours before surgery) and whether performing surgery is safe at that time.

Who was studied?

94 consecutive patients who received bridging enoxaparin therapy.

How was the study done?

The researchers stopped giving warfarin 4 or 5 days before surgery and replaced it with twice-daily injections of enoxaparin 3 days before the surgical procedure. The last injection of enoxaparin was given in the evening and at least 12 hours before surgery. Blood tests were done on all patients just before they went to surgery to see how much anticoagulant was still in the bloodstream.

What did the researchers find?

Blood samples were drawn an average of 14 hours after the last dose of enoxaparin was given and surgery was performed an average of 97 minutes after blood samples were drawn. At least some anticoagulant activity was found in the blood of 99% of the patients. Of these patients, 68% had enough residual enoxaparin effect to be considered fully anticoagulated and 16% had even higher levels.

What were the limitations of the study?

Only 1 type of low-molecular-weight heparin was tested. Other types might have produced different results.

What are the implications of the study?

The last dose of enoxaparin before surgery should be given more than 12 hours and possibly as much as 24 hours before surgery.





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