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.
Pharmacokinetics of estradiol
Vaginal estradiol is available in the forms of tablets, creams, inserts or suppositories, and rings. Vaginal estradiol tablets, creams, and inserts are usually administered once daily to twice weekly, whereas vaginal estradiol rings have a sustained action and are replaced once every 90 days. Vaginal estradiol can be used both as a systemic form of estradiol therapy, and at very low doses to selectively achieve a local vaginal effect without systemic effects, for instance in the treatment of menopausal symptoms such as vaginal atrophy and dryness.