Real-world findings for atrial fibrillation (AF) patients using warfarin point to a significantly higher risk for hemorrhage than reported for clinical trials.
Data for 125,195 AF patients aged 66 years and older who used warfarin between 1997 and 2008 gave an overall rate of hemorrhage of 3.8% per person-year, peaking in the first 30 days of treatment at 11.8% per person-year, and 3.4% per person-year thereafter.
For patients with a CHADS2 score of 4 or above, denoting a high risk for stroke in AF patients, the risk for hemorrhage in the first 30 days was 16.7% per person-year, and 6.0% per person-year thereafter, say Tara Gomes (University of Toronto, Ontario, Canada) and co-authors.
By comparison, patients with a low CHADS2 risk for stroke had lower than average rates of hemorrhage at 1.8% per person-year for a score of 0 and 2.5% per person-year for a score of 1. The rate of hemorrhage was also significantly higher in patients aged over 75 years than younger individuals (4.6 vs 2.9% per person-year).
"The rate of hemorrhage in our study is considerably higher than those reported in randomized controlled trials of warfarin therapy, which have ranged between 1% and 3% per person-year," the team writes in the Canadian Medical Association Journal.
"This difference is likely due to the strict inclusion criteria and close monitoring of patients in clinical trials and the average age of our participants being older than that of patients included in trials."
The patients, all residents of Ontario, were aged a median of 77 years when warfarin was initiated, and 69% had a CHADS2 score of 2 or above for stroke at this time.
Overall, 8.7% of patients attended hospital with hemorrhage over 5 years of follow up, with 18.1% of these individuals dying in hospital or within 7 days of discharge. Mortality was significantly more common after intracranial bleeding than upper or lower gastrointestinal hemorrhage or bleeding at other sites (47.1 vs 14.4, 15.0, and 12.6%, respectively).
"Our study provides timely estimates of warfarin-related adverse events that may be useful to clinicians, patients and policy-makers in light of newly approved and emerging anticoagulant therapies," Gomes et al conclude.
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