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Experts warn against the use of dosing protocols for managing warfarin therapy1
Henry I. Bussey, Pharm.D.
December, 2010
Several clinical pharmacy experts (four of whom are ClotCare Editorial Board members) have taken exception to the positions advocated by some who have promoted a fairly rigid protocol approach to warfarin dosing. As the authors point out, the use of protocols to improve standard dosing of unfractionated heparin and low molecular weight heparins may be a reasonable approach for most patients requiring those medications. However, the large number of factors that can influence the response to warfarin makes dosing of this medication much too complex to rely on a specific proctocol. The authors do endorse the uses of dosing guidelines to help avoid clinical errors in dosing that otherwise can be detrimental in the use of warfarin.
Further evidence of the short-comings of protocol dosing can be illustrated by examining the details of studies that evaluated computer-based dosing of warfarin. Although such computer-based dosing has been cited as a way to improve control of the international normalized ratio (INR), the fact is that such protocol dosing (1) often has to be overridden by the supervising clinical expert, (2) typically makes a small impact on the quality of INR control, and (3) results in what some of us would consider mediocre INR control. For example, in one large, randomized, multi-national study, use of a computer-based dosing protocol resulted in improvement of the INR time in the therapeutic range from 63.4% to 66.8%.2 In this study, however, the computer protocol failed to recommend a dose in approximately 6% of cases, and the recommended dose had to be overridden by the supervising medical expert approximately 27% of the time. Therefore, I agree with the authors that dosing guidelines may help avoid some large and common errors in dosing warfarin, but adhering to a rigid protocol not only is inappropriate, but doing so may be dangerous.
References
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Wittkowsky AK, Spinler SA, Dager W, Gulseth MP, Nutescu EA. Dosing guidelines, not protocols, for managing warfarin therapy. Am J Health-Syst Pharm. 2010; 67:1554-6.
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Poller L, Keown M, Ibrahim, et al. A multicentre randomised assessment of the DAWN AC computer-assisted oral anticoagulant dosage program. Thromb Haemost 2009; 101:487-94.
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