Abstract
Raloxifene, the prototype of the selective estrogen receptor modulators, has been associated with an increased risk of venous thromboembolism. As hemorheological factors may be involved in thrombus formation this placebo‐controlled study investigated whether raloxifene was associated with changes in determinants of blood viscosity. Fifty‐seven post‐menopausal women were randomly assigned to receive placebo, raloxifene 60 mg/day, or raloxifene 120 mg/day for 36 months. Venous blood samples were collected at baseline and at 12‐monthly intervals and used to measure hematocrit, whole blood and plasma viscosity and plasma fibrinogen concentration. Time‐ and treatment‐related changes in the grouped and pooled data was analysed using ANOVA with repeated measures and correlation matrices. The mean values of all the hemorheological indices showed small inconsistent changes within the normal reference range over the 36‐month period of the study. There was a small but significant decrease over time in high shear rate blood viscosity and plasma viscosity in raloxifene‐treated subjects compared to those receiving placebo (p<0.05). Correlation analyses showed the anticipated relationships between blood viscosity and hematocrit and plasma viscosity levels and also between plasma viscosity and plasma fibrinogen concentration. No subject developed a thromboembolic vascular event during the study. These results show that compared with placebo treated‐subjects, long‐term raloxifene treatment in post‐menopausal women, at a dose of either 60 or 120 mg daily, was not associated with adverse changes in hemorheological factors that may contribute to venous thromboembolism.