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.
Estriol (medication)
Estriol is an estrogen, or an agonist of the estrogen receptors, ERα and ERβ. It has been found to possess 11–14% and 18–21% of the relative binding affinities of estradiol for the human ERα and ERβ, respectively, while its relative transactivational capacities at these receptors were 11% and 17%, respectively. In addition to being a ligand of the classical nuclear ERs, estriol is an antagonist of the GPER, a membrane estrogen receptor, at high concentrations. This is in contrast to estradiol, which is an agonist of this receptor. Like other estrogens, estriol does not importantly interact with other steroid hormone receptors.