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.
Pharmacokinetics of estradiol
A single 4 mg intramuscular injection of estradiol cypionate or estradiol valerate has been found to result in maximal plasma levels of estradiol of about 250 pg/mL and 390 pg/mL, respectively, with levels declining to 100 pg/mL (the baseline for estradiol cypionate) by 12 to 14 days. A single 2.5 mg intramuscular injection of estradiol benzoate in patients being administered a GnRH analogue (and hence having minimal baseline levels of estrogen) was found to result in serum estradiol levels of >400 pg/mL at 24 hours post-administration. The differences in the serum levels of estradiol achieved with these different estradiol esters may be explained by their different rates of absorption, as their durations and levels attained appear to be inversely proportional. For instance, estradiol benzoate, which has the shortest duration (4 to 5 days with a single intramuscular injection of 5 mg), produces the highest levels of estradiol, while estradiol cypionate, which has the longest duration (~11 days with 5 mg), produces the lowest levels of estradiol. Estradiol valerate was found to have a duration of 7 to 8 days after a single intramuscular injection of 5 mg.