Estradiol (medication)
Estradiol is available in a variety of different formulations, including oral, intranasal, transdermal/topical, vaginal, injectable, and implantable preparations. An ester may be attached to one or both of the hydroxyl groups of estradiol to improve its oral bioavailability and/or duration of action with injection. Such modifications give rise to forms such as estradiol acetate (oral and vaginal), estradiol valerate (oral and injectable), estradiol cypionate (injectable), estradiol benzoate (injectable), estradiol undecylate (injectable), and polyestradiol phosphate (injectable; a polymerized ester of estradiol), which are all prodrugs of estradiol.
Pharmacodynamics of estradiol
Estradiol is an estrogen, or an agonist of the nuclear estrogen receptors (ERs), the estrogen receptor alpha (ERα) and the estrogen receptor beta (ERβ). According to one study, the value of estradiol for the human ERα is 50 pM (0.05 nM) and for the human ERβ is 200 pM (0.2 nM). Estradiol is also an agonist of the membrane estrogen receptors (mERs), including the G protein-coupled estrogen receptor (GPER), G-coupled membrane estrogen receptor (G-mER), ER-X, and ERx. It is far more potent as an estrogen than are other natural and bioidentical estrogens like estrone and estriol. Given by subcutaneous injection in mice, estradiol is about 10-fold more potent than estrone and about 100-fold more potent than estriol.