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.
Bioidentical hormone replacement therapy
Estriol was part of the United States Pharmacopeia before FDA approval was needed for its use. Its approval was grandfathered in by the FDA until 2008 when the agency banned its use, stating that manufacturers of estriol would have to create a new application and estriol would be treated as a new drug. Its use is not approved by Health Canada; estriol is not available as a pharmaceutical preparation in Canada or the United States, but is a commonly prescribed conventional treatment in other countries and is available as a cream or vaginal suppository in the United Kingdom and the European Union. Estradiol is available as brand-name products in both oral and transdermal forms.