Estradiol stearate
Estradiol stearate (brand name Depofollan), or estradiol octadecanoate, is a naturally occurring steroidal estrogen and an estrogen ester – specifically, the C17β stearate ester of estradiol. It occurs in the body as a very long-lasting metabolite and prohormone of estradiol. In addition, estradiol stearate is or has been available as a pharmaceutical drug for use via depot intramuscular injection. The drug was introduced in 1941 as Depofollan and was the first long-acting estrogen, although it has never been widely used. It has been reported in at least one source to have a duration of at least one month.
Estradiol cypionate
Estradiol cypionate is an estradiol ester, or a prodrug of estradiol. As such, it is an estrogen, or an agonist of the estrogen receptors. The affinity of estradiol valerate for the estrogen receptor has been reported to be 50 times less than that of estradiol, and estradiol valerate and estradiol cypionate have been found to possess similar affinity for the estrogen receptor. Both estradiol cypionate and estradiol valerate are rapidly cleaved into estradiol in the body, and estradiol valerate has been found to be unable to reach target tissues in any concentration of significance. As such, estradiol valerate is regarded as essentially inactive in terms of estrogenic effect itself, acting solely as a prodrug to estradiol, and estradiol cypionate is described as a prodrug of estradiol similarly. Estradiol cypionate is of about 46% higher molecular weight than estradiol due to the presence of its C17β cypionate ester. Because estradiol cypionate is a prodrug of estradiol, it is considered to be a natural and bioidentical form of estrogen.