Preparations & Dosages - The Estrogens

Preparations & Dosages

The dosages of commonly used natural and synthetic preparations are listed in Table 40–1. Although all of the estrogens produce almost the same hormonal effects, their potencies vary both between agents and depending on the route of administration. As noted above, estradiol is the most active endogenous estrogen, and it has the highest affinity for the estrogen receptor. However, its metabolites estrone and estriol have weak uterine effects.

For a given level of gonadotropin suppression, oral estrogen preparations have more effect on the circulating levels of CBG, SHBG, and a host of other liver proteins, including angiotensino-gen, than do transdermal preparations. The oral route of adminis-tration allows greater concentrations of hormone to reach the liver, thus increasing the synthesis of these proteins. Transdermal preparations were developed to avoid this effect. When adminis-tered transdermally, 50–100 mcg of estradiol has effects similar to those of 0.625–1.25 mg of conjugated oral estrogens on gonado-tropin concentrations, endometrium, and vaginal epithelium. Furthermore, the transdermal estrogen preparations do not sig-nificantly increase the concentrations of renin substrate, CBG, and TBG and do not produce the characteristic changes in serum lipids. Combined oral preparations containing 0.625 mg of con-jugated estrogens and 2.5 mg of medroxyprogesterone acetate are available for menopausal replacement therapy. Tablets containing 0.625 mg of conjugated estrogens and 5 mg of medroxyprogester-one acetate are available to be used in conjunction with conju-gated estrogens in a sequential fashion. Estrogens alone are taken on days 1–14 and the combination on days 15–28.