THE ANTIESTROGEN TAMOXIFEN PRODUCES HEMODILUTION IN NORMAL POSTMENOPAUSAL WOMEN

Objectives. To report the effects of the anti-oestrogen tamoxifen on b iochemical and haematological parameters. Design. Randomized, double-b lind comparison of tamoxifen 20 mg per day and placebo, over two years . Setting. A university hospital. Subjects. Forty-six healthy late-pos tmenopausal women (mean, SD time since menopause; 11, seven years). Ma in outcome measures. Blood specimens were drawn in the fasting state a t baseline, six months and two years for measurement of haemoglobin, h aematocrit, erythrocyte mean cell volume, mean erythrocyte haemoglobin , leucocyte count, platelet count, urea, electrolytes, creatinine and albumin. Results. There was a significant decline in the haemoglobin c oncentration in the tamoxifen group (-4.4, 1.2 g/L; mean, SE) and its levels were lower in this group than in those receiving placebo (P = 0 .004). Similarly, haematocrit, erythrocyte count and total leucocyte c ount were lower in those on placebo (P = 0.002, P = 0.01 and P = 0.01, respectively) and platelet count showed a similar trend (P = 0.08). I n the tamoxifen group, the level of serum albumin fell significantly ( -2.2, 0.4 g/L) and was lower throughout the study than that in the pla cebo group (P = 0.006). That of serum urea tended to fall (-0.4, 0.2 m mol L) but the between-groups comparison was not significant (P = 0.18 ). Conclusions. These data suggest that tamoxifen exerts a haemodiluto ry effect in normal postmenopausal women. Since a similar effect has b een reported in response to postmenopausal oestrogen therapy, it is li kely that the observed changes represent another oestrogenic effect of tamoxifen in postmenopausal women. Haemodilution may contribute to th e reduced incidence of cardiovascular disease reported in tamoxifen-tr eated women, and, therefore, its assessment in the new oestrogen agoni sts/antagonists being developed for cardiovascular disease prevention may be important.