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 acetylsalicylate
Estradiol acetylsalicylate, or estradiol 3-acetylsalicylate, is a synthetic estrogen and estrogen ester – specifically, the C3 acetylsalicylic acid (aspirin) ester of estradiol – which was described in the late 1980s and was never marketed. In dogs, the oral bioavailability of estradiol acetylsalicylate was found to be 17-fold higher than that of unmodified estradiol. However, a subsequent study found that the oral bioavailability of estradiol and estradiol acetylsalicylate did not differ in rats (4.3% and 4.2%, respectively), suggestive of a major species difference.