Estradiol (medication)
, estradiol is available in the United States in the following forms:Oral estradiol valerate (Progynova) and other esters of estradiol that are used by injection like estradiol benzoate, estradiol enantate, and estradiol undecylate all are not marketed in the U.S. Polyestradiol phosphate (Estradurin) was marketed in the U.S. previously but is no longer available.
Pharmacokinetics of estradiol
In contrast to estradiol, estrone has very low activity as an estrogen. The affinities of estrone for the human ERs and its estrogenic activity have been reported to be approximately 3 to 4% of those of estradiol. In addition, unlike estradiol and estriol, estrone is not accumulated in target tissues. Because estrone can be transformed into estradiol, most of its activity "in vivo" is actually due to conversion into estradiol. In accordance, dosages of oral and transdermal estradiol that achieve similar levels of estradiol have been found, in spite of markedly elevated levels of estrone with oral estradiol but not with transdermal estradiol, to possess equivalent and non-significantly different potency in terms of clinical measures including suppression of LH and FSH levels, inhibition of bone resorption, and relief of menopausal symptoms such as hot flashes. In addition, estradiol levels were found to correlate with these effects, while estrone levels did not. These findings suggest that estrone contributes very little or not at all to the estrogenic potency of estradiol, while also not antagonizing the estrogenic activity of estradiol. This contradicts some "in vitro" research suggesting that estrone might be able to partially antagonize the actions of estradiol.