Pharmacokinetics of estradiol
Estradiol can be administered in the form of a very long-lasting subcutaneous pellet implant. These implants are replaced once every 6 to 12 months, and can achieve high and very constant circulating levels of estradiol. They are surgically inserted by a trained physician in a medical office or clinic and can be placed into locations including the lower abdomen, lower back, buttocks, or hips. Subcutaneous implants containing 25, 50, and 100 mg estradiol for replacement usually once every 6 months are available as approved pharmaceutical medications. Up to 800 mg estradiol per implantation has been used. Pharmaceutical estradiol implants have been said to be used almost exclusively in the United Kingdom. An estradiol implant has not been approved by the FDA as a pharmaceutical medication in the United States, but hormone implants, including estradiol implants, are available as custom compounded products in this country.
Estrogen ester
Estrogen esters are used in hormone therapy, hormonal contraception, and high-dose estrogen therapy (e.g., for prostate cancer and breast cancer), among other indications. The first estrogen ester to be marketed was estradiol benzoate in 1936, which was followed by many more. One of the most widely used estradiol esters is estradiol valerate, which was first introduced in 1954. Other major estradiol esters that are or have been used in medicine include estradiol acetate, estradiol cypionate, estradiol dipropionate, estradiol enantate, estradiol undecylate, and polyestradiol phosphate (an estrogen ester polymer), as well as the nitrogen mustard alkylating antineoplastic agent estramustine phosphate (estradiol normustine phosphate).