Effect of treatment with low-dose warfarin-aspirin on activated factor VII.

Factor VII is an independent risk factor for ischemic heart disease. We performed a prospective study to evaluate the effect of combined low-dose warfarin-aspirin on activated factor VII (factor VIIa) and to determine if abruptly stopping this treatment is associated with a rebound in the level of factor VIIa. Thirty-three patients with clinically stable coronary artery disease were treated with combined 3 mg warfarin and 80 mg aspirin daily for 8 weeks. The factor VIIa level was measured before treatment, weekly during treatment, and 2 weeks after stopping treatment. The mean percent of pretreatment levels of factor VIIa for weeks 1 through 8 of treatment were 60%, 60%, 72%, 70%, 71%, 70%, 74%, and 87%, respectively (P < .05 compared with pretreatment for weeks 1 through 7 inclusive); 2 weeks after stopping treatment, the level was 122% (95% confidence interval [CI]; 111% to 133%; P < .001 compared with pretreatment). The mean percent level of factor VIIa on-treatment was 74% (P < .001). Factor VIIa is reduced by 26% on average during treatment. This finding provides further rationale for the antithrombotic effect of low-dose warfarin. The results suggest a rebound in the factor VIIa level may occur after treatment is stopped. The potential rebound and its clinical importance should be evaluated by further studies.