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.
Estradiol benzoate
Estradiol benzoate is available in Europe and in other parts of the world. It was previously available for medical use in the United States, but is no longer marketed in this country. However, it is approved and marketed in the United States for veterinary use as a subdermal implant both alone and in combination with the androgen/anabolic steroid trenbolone acetate (brand names Celerin and Synovex, respectively). Outside of the United States, estradiol benzoate is also marketed in combination with progesterone for use as an intramuscular injection.