Fat-soluble 17 beta-estradiol: a way of reducing dosage in steroid hormonal substitution?

Eight ovariectomized women were given 0.5 mg 17 beta-estradiol cyclo-octyl acetate (E2COA) dissolved in arachis oil + 0.15 mg desogestrel, and 2 mg micronized 17 beta-estradiol (mE2) + 0.15 mg desogestrel orally in a crossover fashion for 20 days each. The preparations were taken on 10 days together with a meal, on 10 days 3 hours after a meal. Blood samplings were performed 3 h after capsule ingestion for analysis of serum estradiol (S-E2), estrone (S-E1) and sex hormone binding globulin (SHBG). Before treatment, all women had climacteric complaints. During treatment these symptoms were alleviated and no discomfort was reported. No differences in serum levels of estrogens were found in either of the preparations when capsules were taken with or without food. However, serum levels of E2 were found to be 100% higher per mg substance given after E2COA vis-à-vis mE2. This indicates either a delayed breakdown and/or a better resorption. The E1/E2 ratio after E2COA was only half that after mE2 intake. This hints at another route of resorption. SHBG concentrations were somewhat elevated following mE2 administration, whereas a slight decrease was found after E2COA. The resulting post-treatment difference was significant, suggesting a less estrogenic liver effect by E2COA. No accumulation of E2 or E1 was seen after either of the preparations. Our findings support the hypothesis that E2COA, being fat soluble, is resorbed via the lymphatic system. By avoiding the first liver pass the dosage of estrogen can be halved.