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* From St. Joseph’s Hospital, Hamilton, Ontario, Canada.
Correspondence to: Mark A Crowther, MD, MSc, McMaster University, St. Joseph’s Hospital, 50 Charlton Ave East, Hamilton, Ontario, Canada L8N 4A6; e-mail: crowthrm{at}mcmaster.ca
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Abstract |
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Design: Cross-sectional physician survey.
Participants: Members of the Canadian Society of Internal Medicine practicing in Ontario, Canada.
Measurements and results: Physicians were asked to provide management preferences in six clinical scenarios describing warfarin-induced excessive AC. The scenarios represent various combinations of international normalized ratio (INR) value, treatment setting, and presence and severity of bleeding. In scenarios with INRs < 5.2 without bleeding, conservative approaches complying with the ACCP guidelines, such as withholding warfarin or reducing its dose, were most common. In scenarios with high INRs (ie, > 7.1) and/or bleeding, the selection of vitamin K in any form ranged between 71% and 82%. However, compliance with the ACCP-recommended doses and the routes of vitamin K administration ranged from 1 to 10%. In five of the six scenarios, subcutaneous injection, a route not recommended by the ACCP, was the most common method of vitamin K delivery.
Conclusions: Physician preferences for the reversal of warfarin-induced excessive AC were highly variable and, in most cases, did not follow the recommendations of the ACCP consensus guidelines. Furthermore, the widespread reported use of subcutaneous vitamin K is concerning because this route of vitamin K administration has been demonstrated to be less effective than IV administration of vitamin K. These findings highlight the need for randomized controlled trials to compare the efficacy of different routes of administration of vitamin K for warfarin-associated coagulopathy.
Key Words: coagulopathy • Ontario • survey • vitamin K • warfarin
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Introduction |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Materials and Methods |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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To ensure a complete data set, a priori criteria were established to exclude incomplete or irrelevant surveys from the analysis. The exclusion criteria were the following: (1) the physician does not supervise patients who are receiving warfarin therapy or did not indicate the frequency of his or her supervision of those patients; (2) the physician no longer resides at the address provided; (3) the physician has retired from medical practice; or (4) the survey was returned incomplete (surveys with minor omissions such as not specifying practice setting were included).
Analysis
The analysis consisted of two parts: first, the proportion
of respondents who selected each treatment option for the six scenarios
was determined. Preferences for the route of administration and the
dose of vitamin K also were determined. Second, the proportion of
respondents who complied with the 1998 American College of Chest
Physicians (ACCP) guidelines (see the Appendix)
for the reversal of warfarin-associated coagulopathy was determined for
each scenario.
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Results |
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TOPAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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Response to Surveys
Treatment preferences are presented in Table 3
. Scenarios 1, 2, 3, and 6 describe asymptomatic patients with INR
values between 4.5 and 8.6. In these scenarios, the most frequent
treatment selections were either the temporary withholding of warfarin
therapy or the continuing of warfarin therapy at a reduced dose. In
scenario 1, which described a patient with an INR of 8.6, 37% of
respondents would administer vitamin K, whereas in the other three
scenarios, which presented patients with INR values of 4.5 to 7.1, 1 to
12% of respondents would administer vitamin K. Scenarios 4 and 5
describe patients with elevated INR values and bleeding. In scenario 4,
which described a patient with retinal bleeding, 71% of respondents
would administer vitamin K, and 87% would administer some form of
coagulation factor replacement (59% would administer it in concert
with vitamin K). In scenario 5, which described a patient with
hematuria, 82% of respondents would administer vitamin K, and 42%
would administer some form of coagulation factor replacement (31%
would administer it in concert with vitamin K) [comparison of the use
of vitamin K, p = 0.05; comparison for the use of coagulation factor
replacement, p < 0.001].
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Compliance With ACCP Guidelines
Scenarios 3 and 6, describing patients with asymptomatic
INR values of < 5.0, were most appropriately treated by
recommendation 1 of the ACCP guidelines (see the Appendix). The
treatment recommendation was followed by 99% and 96% of respondents,
respectively. Scenarios 1 and 2, describing patients with INR values
between 5.0 and 9.0 without bleeding, were best treated by
recommendation 2 in the ACCP guidelines. In scenario 1, 62% of
respondents complied with the recommended treatment, while 86% of
respondents complied with the recommended treatment for scenario 2.
Scenario 5 presents a patient best treated following recommendation 3
(INR, > 9.0 without serious bleeding), and 1% of respondents treated
this patient, as recommended, with oral vitamin K therapy alone. If the
hematuria reported in this case is regarded as serious bleeding, 9% of
respondents treated the patient as recommended in recommendation 4. The
retinal bleeding described in scenario 4 satisfies the condition of
serious bleeding and should be treated as recommended by recommendation
4. Only 10% of respondents followed the guideline and administered 10
mg IV vitamin K (with 9% selecting vitamin K administration in
addition to FFP or PCC, and 1% selecting vitamin K administration
alone).
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Discussion |
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Our results suggest that general internists in Ontario are aware that vitamin K therapy is a safe and effective method for reversing warfarin-induced excessive AC; however, the variety of routes and doses selected by respondents highlights the inconsistency with which patients are treated with vitamin K. This is noteworthy because the inappropriate use of vitamin K therapy, particularly in excessive doses, may be more hazardous than the lack of vitamin K use. Across the six scenarios, 6% of all respondents who selected vitamin K therapy chose doses of 20 to 25 mg, doses that could result in "overcorrection" of the INR, placing the patient at risk of thromboembolic complications. It is also noteworthy that physicians preferred the subcutaneous route of vitamin K administration, a route that is less effective in reestablishing a therapeutic level of AC than the IV route.8 9
Evidence-based guidelines for the clinical management of patients with warfarin-induced excessive AC are available from the ACCP.5 10 The treatment recommendations for the reversal of excessive warfarin AC are graded C2, indicating that the studies used to formulate these guidelines were observational in nature. These guidelines suggest the advisability of administration of oral vitamin K to patients with INRs > 5.0. However, the actual frequency with which oral vitamin K therapy is administered to such patients is unknown. Previous reported rates of oral vitamin K therapy have been low, ranging between 5% and 20%.1 6 7 Despite the relatively frequent use of vitamin K in the scenarios presented in this survey, compliance with ACCP recommendations specifying the appropriate dose and route of vitamin K was considerably lower. The disparity between vitamin K usage and ACCP compliance is highlighted by scenario 5, which described painless hematuria. The greatest proportion of respondents selected vitamin K therapy for this scenario (82%), but only 1% of respondents complied with the ACCP guidelines with respect to dose and route of administration.
There are several characteristics that support the validity and generalizability of the findings of this survey. First, the treatment options presented in the survey are likely a valid representation of the usual clinical practice, as these options were selected by 96% and 100% of respondents, depending on the scenario. Second, approximately two thirds of respondents frequently supervised patients receiving warfarin therapy, and physicians who did not supervise such patients were excluded from the analysis. Finally, the response rate to the survey was 59%, which is consistent with the response rate seen in other physician surveys dealing with anticoagulant management.11 12 13 The primary limitation of the survey results is that they reflect self-reported, and not confirmed, management approaches.
In summary, our survey suggests that there is considerable variability in the management of patients with excessive warfarin-associated AC. The lack of widely accepted treatments for this problem reaffirms the need for randomized controlled trials to compare the efficacy of different routes of administration of vitamin K for warfarin-associated coagulopathy.
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Footnotes |
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This research was funded, in part, by the Canadian Institutes for Health Research. Dr. Crowther holds a Research Scholarship from the Canadian Institutes of Health Research. Dr. Douketis holds a Research Scholarship from the Heart and Stroke Foundation of Canada.
Received for publication November 17, 2000. Accepted for publication June 4, 2001.
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References |
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This article has been cited by other articles:
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  J P Hanley Warfarin reversal J. Clin. Pathol., November 1, 2004; 57(11): 1132 - 1139. [Abstract] [Full Text] [PDF]
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 S. E. Wilson, H. G. Watson, and M. A. Crowther Low-dose oral vitamin K therapy for the management of asymptomatic patients with elevated international normalized ratios: a brief review Can. Med. Assoc. J., March 2, 2004; 170(5): 821 - 824. [Abstract] [Full Text] [PDF]
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 M. A. Crowther, J. D. Douketis, T. Schnurr, L. Steidl, V. Mera, C. Ultori, A. Venco, and W. Ageno Oral Vitamin K Lowers the International Normalized Ratio More Rapidly Than Subcutaneous Vitamin K in the Treatment of Warfarin-Associated Coagulopathy: A Randomized, Controlled Trial Ann Intern Med, August 20, 2002; 137(4): 251 - 254. [Abstract] [Full Text] [PDF]
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