Estradiol (medication)
Estradiol is also available in the U.S. in combination with progestogens for the treatment of menopausal symptoms and as a combined hormonal contraceptive:Estradiol and estradiol esters are also available in custom preparations from compounding pharmacies in the U.S. This includes subcutaneous pellet implants, which are not available in the United States as FDA-approved pharmaceutical drugs. In addition, topical creams that contain estradiol are generally regulated as cosmetics rather than as drugs in the U.S. and hence are also sold over-the-counter and may be purchased without a prescription on the Internet.
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.