Patients prescribed common blood thinner have three-times the risk of stroke during first month of treatment: study

Patients with atrial fibrillation (irregular heart beat) who are newly prescribed warfarin (a common blood thinner), are at a three-times increased risk of ischemic stroke during the first 30 days of warfarin therapy compared to the remaining five years of follow-up, according to new research conducted at the Institute for Clinical Evaluative Sciences (ICES).

“Warfarin therapy is routinely prescribed in atrial fibrillation to decrease ischemic stroke risk. However, our study demonstrates that the risk of stroke is highest in the first 30 days of starting warfarin therapy. Little is known about the absolute risk of stroke after warfarin initiation, how this changes over time, or whether therapy duration and patient comorbidities play a role,” said Jennifer Tung, Pharmacist, Sunnybrook Health Sciences Centre and lead author of the study.

Atrial fibrillation is a major risk factor for stroke and there is strong evidence that anticoagulation therapy with warfarin reduces this risk.

The population-based cohort study identified 148,446 patients aged 66-years and older with atrial fibrillation who received warfarin between April 1, 1997 to March 31, 2010 in Ontario. The study found:

• 6,006 patients experienced an ischemic stroke within 5 years of starting warfarin.
• The rate of ischemic stroke is more than three-times higher during the first 30 days of warfarin therapy compared to the remaining 5 years of follow-up.
• This increased risk has considerable clinical consequences. Among the patients hospitalized for ischemic stroke, 27.3 per cent died in hospital or within 7 days of discharge.

“Elevated risk of both ischemic stroke and hemorrhage upon warfarin initiation are major challenges to anticoagulation therapy, and highlights the need for close patient monitoring early in therapy to mitigate this risk, particularly in elderly patients with multiple stroke risk factors,” added Tung.

Authors: Jennifer M. Tung, Muhammad M. Mamdani, David N. Juurlink, J. Michael Paterson, Moira K. Kapral, Tara Gomes.

“Rates of ischemic stroke during warfarin treatment for atrial fibrillation,” was published today in Stroke.

ICES is an independent, non-profit organization that uses population-based health information to produce knowledge on a broad range of healthcare issues. Our unbiased evidence provides measures of health system performance, a clearer understanding of the shifting healthcare needs of Ontarians, and a stimulus for discussion of practical solutions to optimize scarce resources. ICES knowledge is highly regarded in Canada and abroad, and is widely used by government, hospitals, planners, and practitioners to make decisions about care delivery and to develop policy.

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