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Research

Rates of hemorrhage during warfarin therapy for atrial fibrillation

Tara Gomes, Muhammad M. Mamdani, Anne M. Holbrook, J. Michael Paterson, Chelsea Hellings and David N. Juurlink
CMAJ February 05, 2013 185 (2) E121-E127; DOI: https://doi.org/10.1503/cmaj.121218
Tara Gomes
The Leslie Dan Faculty of Pharmacy (Gomes, Mamdani) and the Department of Health Policy, Management, and Evaluation (Juurlink, Mamdani, Paterson), University of Toronto; the Institute for Clinical Evaluative Sciences (Juurlink, Paterson, Hellings, Mamdani); the Sunnybrook Research Institute (Juurlink); and the Keenan Research Centre of the Li Ka Shing Knowledge Institute (Mamdani), St. Michael’s Hospital, Toronto, Ont.; the Department of Family Medicine (Paterson) and Division of Clinical Pharmacology & Therapeutics (Holbrook), McMaster University; and the Centre for Evaluation of Medicines (Holbrook, Paterson), St. Joseph’s Healthcare, Hamilton, Ont.
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  • For correspondence: tara.gomes@ices.on.ca
Muhammad M. Mamdani
The Leslie Dan Faculty of Pharmacy (Gomes, Mamdani) and the Department of Health Policy, Management, and Evaluation (Juurlink, Mamdani, Paterson), University of Toronto; the Institute for Clinical Evaluative Sciences (Juurlink, Paterson, Hellings, Mamdani); the Sunnybrook Research Institute (Juurlink); and the Keenan Research Centre of the Li Ka Shing Knowledge Institute (Mamdani), St. Michael’s Hospital, Toronto, Ont.; the Department of Family Medicine (Paterson) and Division of Clinical Pharmacology & Therapeutics (Holbrook), McMaster University; and the Centre for Evaluation of Medicines (Holbrook, Paterson), St. Joseph’s Healthcare, Hamilton, Ont.
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Anne M. Holbrook
The Leslie Dan Faculty of Pharmacy (Gomes, Mamdani) and the Department of Health Policy, Management, and Evaluation (Juurlink, Mamdani, Paterson), University of Toronto; the Institute for Clinical Evaluative Sciences (Juurlink, Paterson, Hellings, Mamdani); the Sunnybrook Research Institute (Juurlink); and the Keenan Research Centre of the Li Ka Shing Knowledge Institute (Mamdani), St. Michael’s Hospital, Toronto, Ont.; the Department of Family Medicine (Paterson) and Division of Clinical Pharmacology & Therapeutics (Holbrook), McMaster University; and the Centre for Evaluation of Medicines (Holbrook, Paterson), St. Joseph’s Healthcare, Hamilton, Ont.
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J. Michael Paterson
The Leslie Dan Faculty of Pharmacy (Gomes, Mamdani) and the Department of Health Policy, Management, and Evaluation (Juurlink, Mamdani, Paterson), University of Toronto; the Institute for Clinical Evaluative Sciences (Juurlink, Paterson, Hellings, Mamdani); the Sunnybrook Research Institute (Juurlink); and the Keenan Research Centre of the Li Ka Shing Knowledge Institute (Mamdani), St. Michael’s Hospital, Toronto, Ont.; the Department of Family Medicine (Paterson) and Division of Clinical Pharmacology & Therapeutics (Holbrook), McMaster University; and the Centre for Evaluation of Medicines (Holbrook, Paterson), St. Joseph’s Healthcare, Hamilton, Ont.
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Chelsea Hellings
The Leslie Dan Faculty of Pharmacy (Gomes, Mamdani) and the Department of Health Policy, Management, and Evaluation (Juurlink, Mamdani, Paterson), University of Toronto; the Institute for Clinical Evaluative Sciences (Juurlink, Paterson, Hellings, Mamdani); the Sunnybrook Research Institute (Juurlink); and the Keenan Research Centre of the Li Ka Shing Knowledge Institute (Mamdani), St. Michael’s Hospital, Toronto, Ont.; the Department of Family Medicine (Paterson) and Division of Clinical Pharmacology & Therapeutics (Holbrook), McMaster University; and the Centre for Evaluation of Medicines (Holbrook, Paterson), St. Joseph’s Healthcare, Hamilton, Ont.
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David N. Juurlink
The Leslie Dan Faculty of Pharmacy (Gomes, Mamdani) and the Department of Health Policy, Management, and Evaluation (Juurlink, Mamdani, Paterson), University of Toronto; the Institute for Clinical Evaluative Sciences (Juurlink, Paterson, Hellings, Mamdani); the Sunnybrook Research Institute (Juurlink); and the Keenan Research Centre of the Li Ka Shing Knowledge Institute (Mamdani), St. Michael’s Hospital, Toronto, Ont.; the Department of Family Medicine (Paterson) and Division of Clinical Pharmacology & Therapeutics (Holbrook), McMaster University; and the Centre for Evaluation of Medicines (Holbrook, Paterson), St. Joseph’s Healthcare, Hamilton, Ont.
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  • Re:Use of warfarin and absolute risk of hemorrhagic stroke in a population-based cohort
    Murray B. Trusler
    Posted on: 26 September 2013
  • Use of warfarin and absolute risk of hemorrhagic stroke in a population-based cohort
    Antonio Gonzalez-Perez
    Posted on: 15 February 2013
  • Real World Ontario ICH Rates on Warfarin Lower Than Dabigatran, Rivaroxaban and Apixaban Pivotal RCT Findings
    Murray B. Trusler MD, MBA, FCFP
    Posted on: 30 January 2013
  • Posted on: (26 September 2013)
    Page navigation anchor for Re:Use of warfarin and absolute risk of hemorrhagic stroke in a population-based cohort
    Re:Use of warfarin and absolute risk of hemorrhagic stroke in a population-based cohort
    • Murray B. Trusler, Rural and Remote Family Physician

    It is interesting to note that the UK has an overall ICH rate of 0.17% in the real world (1). This is lower than the 0.2% ICH rate in Ontario, Canada (2). One major difference between the management of warfarin in the UK and Ontario, is the use of computer decision support software and INR point of care testing. 2,500 GP clinics in the UK use INRstar, a web based computer decision support software tool, in conjunctio...

    Show More

    It is interesting to note that the UK has an overall ICH rate of 0.17% in the real world (1). This is lower than the 0.2% ICH rate in Ontario, Canada (2). One major difference between the management of warfarin in the UK and Ontario, is the use of computer decision support software and INR point of care testing. 2,500 GP clinics in the UK use INRstar, a web based computer decision support software tool, in conjunction with CoaguChek XS INR POCT monitoring (3). This program is used in the management of one third of patients prescribed warfarin in the UK. 78% of their patients have TTR's >65% (3). It should be noted that the pivotal RCTs compared the NOACs to warfarin at TTR's under 65% (RE-LY 64%, Rocket AF 55%, Aristotle 62%). There is grade 1A evidence for the use of computer decision support software (4), and yet it is an almost undiscovered tool in Canada.

    In view of the higher ICH rates in the treatment arms of the pivotal NOAC RCTs (dabigatran 150 0.3%, rivaroxaban 0.5%, apixaban 0.33%), I agree with Antonio Gonzalez-Perez David Gaist and Luis A. Garcia Rodriguez. We need real world data to establish comparative NOAC ICH rates. This would be particularly useful in the UK and Ontario where robust data exists on the warfarin experience.

    For now, there is no real world evidence for condemning warfarin as a dangerous drug causing high rates of ICH in Ontario and the UK. There is clearly a potential danger in extrapolating RCT data from international studies to local contexts. This may well prove to be a very good example. We need real world data in the local context to provide the relevant evidence.

    References

    1. Antonio Gonzalez-Perez David Gaist, Luis A. Garcia Rodriguez Spanish Centre for Pharmacoepidemiologic Research (CEIFE), Madrid, Spain; Andalusian Bioinformatics

    2. Tara Gomes, Muhammad M. Mamdani, Anne M. Holbrook, J. Michael Paterson, Chelsea Hellings, and David N. Juurlink Can. Med. Assoc. J. 2013 185:E121-E127; doi:10.1503/cmaj.121218 Rates of hemorrhage during warfarin therapy for atrial fibrillation

    3. Personal meeting with INRstar, Cornwall, England, September, 2013

    4. British Committee for Standards in Haematology. Guidelines on Oral Anticoagulation with Warfarin - fourth edition. British Journal of Haematology. Vol. 154 Issue 3. August 2011.

    Conflict of Interest:

    VP of INR Online Canada Ltd.

    Show Less
    Competing Interests: None declared.
  • Posted on: (15 February 2013)
    Page navigation anchor for Use of warfarin and absolute risk of hemorrhagic stroke in a population-based cohort
    Use of warfarin and absolute risk of hemorrhagic stroke in a population-based cohort
    • Antonio Gonzalez-Perez
    • Other Contributors:

    We have read with great interest the recent paper by Gomes et al. published in the journal (1), which highlights the importance of quantifying the risk of bleeding episodes associated to warfarin now that new therapeutic options are becoming available.

    We have just completed a population-based cohort study using THIN, a primary care database from the UK, aimed at estimating the incidence rate of hemorrhagic str...

    Show More

    We have read with great interest the recent paper by Gomes et al. published in the journal (1), which highlights the importance of quantifying the risk of bleeding episodes associated to warfarin now that new therapeutic options are becoming available.

    We have just completed a population-based cohort study using THIN, a primary care database from the UK, aimed at estimating the incidence rate of hemorrhagic stroke in the general population (2). Briefly, we identified individuals aged 20 through 89 years between 2000 and 2008 and followed them for an average of 5.8 years. Overall we ascertained 1797 cases of intracerebral hemorrhage and 1340 cases of subarachnoid hemorrhage. We wanted to explore if we could reproduce the estimates of hemorrhagic stroke risk among new users of warfarin reported by Gomes et al using our data from the UK.

    We found that, among those aged 65 years and above who were prescribed warfarin for the first time, the incidence rate of hemorrhagic stroke after starting on warfarin was 294.6 cases per 100,000 person-years (95%CI: 118.5-606.1) within the first 30 days and 165.6 cases per 100,000 person-years (95%CI: 136.6-199.2) during the overall follow-up. These figures correspond to annual rates of 0.29% per person-year for the 30-day period, and 0.17% per person-year for the overall follow-up period. Both estimates are extremely similar to those reported by Gomes et al for intracranial hemorrhage: 0.4% for the initial 30 days and 0.2% overall. In conclusion, we have been able to reproduce similar estimates of absolute risk to those reported by Gomes et al in a different population (UK) when using an analogous design despite different source of information. Along with their study, our results serve to underline the importance of performing this type of study in a population-based setting, which mimics the real-life scenario of a clinician better than estimates based on clinical trial data. It is therefore important that newer anticoagulant drugs that have emerged in recent years should also be subjected to population-based studies performed with valid sources of information and valid methods in years to come.

    1. Gomes T, Mamdani MM, Holbrook AM, Paterson JM, Hellings C, Juurlink DN. Rates of hemorrhage during warfarin therapy for atrial fibrillation. CMAJ 2012 Nov 26 (doi:10.1503/cmaj.121218)

    2. Gaist D, Wallander MA, Gonzalez-Perez A, Garcia-Rodriguez LA. Incidence of hemorrhagic stroke in the general population: validation of data from The Health Improvement Network. Pharmacoepidemiol Drug Saf 2012 Dec 10 (doi: 10.1002/pds.3391)

    Conflict of Interest:

    The original study was funded by Bayer Pharma AG.

    Show Less
    Competing Interests: None declared.
  • Posted on: (30 January 2013)
    Page navigation anchor for Real World Ontario ICH Rates on Warfarin Lower Than Dabigatran, Rivaroxaban and Apixaban Pivotal RCT Findings
    Real World Ontario ICH Rates on Warfarin Lower Than Dabigatran, Rivaroxaban and Apixaban Pivotal RCT Findings
    • Murray B. Trusler MD, MBA, FCFP, Rural and Remote Family Physician

    I read with interest, the CMAJ early release article "Rates of hemorrhage during warfarin therapy for atrial fibrillation" (November 26, 2012) by Gomes et al. It is of great importance as it is Canadian data, a huge sample size (125,195 patients) and represents the real world. The ICH rate in this study is 0.2% over 5 years for warfarin, including all comers and the warfarin initiation period (first 30 days) during whic...

    Show More

    I read with interest, the CMAJ early release article "Rates of hemorrhage during warfarin therapy for atrial fibrillation" (November 26, 2012) by Gomes et al. It is of great importance as it is Canadian data, a huge sample size (125,195 patients) and represents the real world. The ICH rate in this study is 0.2% over 5 years for warfarin, including all comers and the warfarin initiation period (first 30 days) during which the ICH rate was 0.4% (personal communication with the author). This rate of 0.2% accurately reflects the management of warfarin in Ontario over a 13 year period (mean 5 years).

    To put the ICH rate in perspective, I have attached the following list showing comparative ICH rates in each of the NOAC trials (RE-LY - 44 countries, Rocket AF - 45 countries, Aristotle - 39 countries and Sportif V - US and Canada only). None beats warfarin as managed in Ontario.

    Warfarin (Ontario) Real World 0.2% - Tara Gomes et al, Dabigatran 110 mg (RE-LY) 0.23%, Ximelegatran (Sportif V) 0.23%, Dabigatran 150 mg (RE-LY) 0.3%, Warfarin (Sportif V) 0.3%, Apixaban (Aristotle) 0.33%, Rivaroxaban (Rocket AF) 0.5%, Warfarin (Rocket AF) 0.7%, Warfarin (RE-LY) 0.74%, Warfarin (Aristotle) 0.8%.

    The bottom line: The NOACs have been promoted heavily on the basis of a much lower rate of ICH than warfarin. We now know that this is clearly not true for Ontario (and likely Canada as a whole - more data required) in the real world. The reason for the disparity is trial bias based on the NOAC trials using 39-45 countries except for Sportif V (North American trial). In these trials most of the countries manage warfarin poorly compared to Canada (e.g. Canada ranked 8th out of 44 countries in RE-LY).

    This demonstrates the fallacy in using international data to come to local conclusions (internal validity issue) in situations where the quality of healthcare systems is a pivotal factor. Physicians and consumers need to know that higher ICH rates with warfarin vs. NOAC trial data do not exist in Ontario in the real world at present.

    If the ICH rates do not hold up, it is highly unlikely that the primary end-points in the pivotal NOAC trials will hold up either, as stroke and systemic embolism includes hemorrhagic stroke (a component of ICH). Further analysis is required.

    Of additional note is a December 18, 2012 Australian Ministry of Health report on anticoagulation management noting "that patients would benefit greatly if barriers to the use of existing therapies such as warfarin were dealt with" (Hon Tanya Plibersek MP, Minister for Health, Australia - Media Release).

    Quo vadis?

    1. The current 2012 CCS CPG needs to be reconsidered as the new evidence (relatively low rates of ICH with warfarin) no longer supports the earlier assumptions and recommendations.

    2. We need to recognize that some international studies cannot rationally drive national CPGs in Canada. This is true where the trial results and conclusions are directly dependent upon the quality of the health care system managing the therapy and there is significant performance variability across the participating systems.

    3. It is possible to improve warfarin therapy in Canada through the use of computer decision support software and INR point of care testing. Perhaps, we should follow Australia's lead and deal with the "barriers" to the use of warfarin in our country. We have the tools to significantly raise our performance. We need the will and support to implement their use.

    4. It is time to embrace the routine measurement of warfarin management performance through the use of real time INR average time in therapeutic range (TTR) measurements. TTR is the gold standard for measuring the quality of warfarin management and can only be readily measured using computer software. All warfarin managers (self testing patients and healthcare professionals alike) need to have access to this technology, in order to properly measure the quality of warfarin dosing performance and to reduce the incidence of strokes and hemorrhages in Canada.

    Conflict of Interest:

    Dr. Trusler is VP of INR Online Canada Ltd., a company that develops a computer decision support tool for warfarin management.

    Show Less
    Competing Interests: None declared.
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Rates of hemorrhage during warfarin therapy for atrial fibrillation
Tara Gomes, Muhammad M. Mamdani, Anne M. Holbrook, J. Michael Paterson, Chelsea Hellings, David N. Juurlink
CMAJ Feb 2013, 185 (2) E121-E127; DOI: 10.1503/cmaj.121218

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Rates of hemorrhage during warfarin therapy for atrial fibrillation
Tara Gomes, Muhammad M. Mamdani, Anne M. Holbrook, J. Michael Paterson, Chelsea Hellings, David N. Juurlink
CMAJ Feb 2013, 185 (2) E121-E127; DOI: 10.1503/cmaj.121218
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