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
Estriol, also known as 16α-hydroxyestradiol or as estra-1,3,5(10)-triene-3,16α,17β-triol, is a naturally occurring estrane steroid with double bonds between the C1 and C2, C3 and C4, and C5 and C10 positions and hydroxyl groups at the C3, C16α, and C17β positions. The name "estriol" and the abbreviation "E3" were derived from the chemical terms "estrin" (estra-1,3,5(10)-triene) and triol (three hydroxyl groups).