Antiestrogenic potency of toremifene and tamoxifen in postmenopausal women

In this nonblinded, controlled multicenter trial, postmenopausal women were randomly assigned to receive graded doses of toremifene and tamoxifen or no antiestrogen to assess dose-response levels and evaluation methodology. For standardization, transdermal estradiol (Estraderm-Ciba Geigy) was applied to all women for 38 days. The antiestrogens were added on days 29-38. For control and all treatment groups, there were no significant changes in serum chemistries or serum hormone levels, nor were there differences in adverse effects. The use of continuous estradiol precluded any meaningful assessment of the estrogenicity of tamoxifen or toremifene. As measured by vaginal superficial cytologic cell count changes, the antiestrogenic activity of toremifene doses ranging from 20 to 200 mg/day could not be distinguished from that of 20 mg/day of tamoxifen, the clinically recommended dose in North America.