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National Institute of Clinical Studies Scholar PhD Candidate Unit for Medication Outcomes Research and Education School of Pharmacy University of Tasmania Private Bag 83 Hobart Tasmania, Australia 7001 fax 61 3 6226 7627 Luke.Bereznicki{at}utas.edu.au
National Institute of Clinical Studies Fellow Unit for Medication Outcomes Research and Education School of Pharmacy University of Tasmania
Professor of Pharmacy Unit for Medication Outcomes Research and Education School of Pharmacy University of Tasmania
Published Online, July 11, 2006. www.theannals.com, DOI 10.1345/aph.1G407a
To demonstrate that a reduced initiation dosage of warfarin could be beneficial in this setting, we conducted a comparison of results from Rahman et al.'s investigation with those from similar patients initiated on warfarin at the Royal Hobart Hospital (RHH), Tasmania, Australia, following heart valve surgery (Table 1). This was part of an ongoing study of warfarin initiation at RHH. An initiation dose of 3 mg was given for the first 2 days and then adjusted according to the INR to allow for pacing wire removal at an INR lower than 1.6; the dose was then adjusted to achieve a therapeutic INR prior to discharge. The 3 mg regimen used at the RHH resulted in a much lower incidence of INRs greater than 4 during initiation, which is a commonly cited indicator of excessive anticoagulation during initiation. Importantly, Rahman et al. excluded patients who received drugs that are known to interact with warfarin to enable them to better study warfarin sensitivity; in our cohort, all patients received prophylactic doses of intravenous cefazolin following surgery. Additionally, significant numbers of patients received amiodarone and oral antibiotics during the initiation of warfarin; these drugs are known to elevate the INR.3
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Despite the presence of these interacting medications, a much lower incidence of elevated INRs was demonstrated in our cohort. Indeed, for elderly patients in general, there is a growing body of evidence to suggest that initiation doses of warfarin of less than 5 mg/day may be beneficial.4,5 It is likely that overaggressive initial dosing of warfarin in the elderly population is at least partly responsible for the higher rates of bleeding that have been reported in the early phase of treatment. It is logical to assume that improving the quality of warfarin initiation in cardiothoracic patients will reduce the rate of major bleeding and improve patient outcomes. Despite the demonstrated sensitivity to warfarin after heart valve surgery, it may be possible to achieve lower rates of excessive anticoagulation during initiation, even in the presence of interacting drugs and advanced age, by using a 3 mg rather than a 5 mg dose for the first 2 days of therapy.
Footnotes
Mr. Bereznicki is funded by a National Institute of Clinical Studies Scholarship.
References
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