Low-intensity warfarin may be inferior to standard-intensity warfarin for preventing VTE after joint arthroplasty

Reference

Gage BF, Bass AR, Lin H, et al. Effect of low-intensity vs standard-intensity warfarin prophylaxis on venous thromboembolism or death among patients undergoing hip or knee arthroplasty. A randomized clinical trial. JAMA 2019;322(9):834-42.

Synopsis

Various guidelines recommend different target INRs of 1.8 vs. 2.5 after elective hip or knee arthroplasty. These investigators identified patients, aged 65 years or older with a life expectancy more than 6 months, planning to undergo elective hip or knee arthroplasty. Study subjects (n = 1650) randomly received (concealed allocation assignment) warfarin at the time of surgery dosed using standard regimens to a target INR of 1.8 vs 2.5. Patients with atrial fibrillation were excluded. The primary outcome was a composite of VTE with 60 days, or death within 30 days of surgery. All asymptomatic patients underwent lower-extremity duplex ultrasound screening for DVT at 1 month. Individuals masked to study group assignment assessed duplex ultrasound images and imaging tests for pulmonary embolisms. Complete follow-up occurred for all but one patient at 90 days. Using intention-to-treat analysis and an absolute difference of 3% or less in VTE (with most events being asymptomatic) as the margin of inferiority, the rate of the primary outcome occurred in 5.1% of the low-intensity group and 3.8% of the standard-intensity group. Although the absolute difference (1.3%) was less than 3%, the higher bound of the 95% CI exceeded 3% (3.05%); thus, not meeting the prespecified criteria for noninferiority. No significant group differences occurred in major bleeding events within 30 days.