Robert Zeller, MD
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Zeller R.; Randomized Trial of Warfarin Nomograms. Ann Intern Med. 2004;140:489. doi: 10.7326/0003-4819-140-6-200403160-00024
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Published: Ann Intern Med. 2004;140(6):489.
TO THE EDITOR:
Kovacs and colleagues (1) recommended a 10-mg warfarin nomogram for outpatient treatment of acute venous thromboembolism as being superior to a 5-mg regimen (1). I should point out that using the INR as measure of efficacy early in the course of therapy may give one false assurance (2). Factor VII is affected early and will prolong the INR. However, lowering levels of factor VII does not prevent thromboembolism. Lowering levels of factor IX and factor X (the next 2 factors to be altered) does, but this takes longer. I note that 3 of Kovacs and colleagues' patients in the 10-mg group had venous thromboembolism by 90 days versus none in the 5-mg group. Although this does not reach statistical significance (P= 0.09), there may be a trend favoring the 5-mg dose with low-molecular-weight heparin given for a longer period. A larger study might have revealed a statistical difference, should one truly exist. I therefore would recommend caution before accepting the 10-mg regimen.
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Print ISSN: 0003-4819 | Online ISSN: 1539-3704
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