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 anthranilate
Estradiol anthranilate, or estradiol 3-anthranilate, is a synthetic estrogen and estrogen ester – specifically, the C3 anthranilic acid ester of estradiol – which was described in the late 1980s and was never marketed. In dogs, the oral bioavailability of estradiol anthranilate was found to be 5-fold higher than that of unmodified estradiol. However, a subsequent study found that the oral bioavailability of estradiol and estradiol anthranilate did not differ considerably in rats (4.3% and 3.2%, respectively), suggestive of a major species difference.