Estradiol sulfate
As the sodium salt, sodium estradiol sulfate, E2S is present as a minor constituent (0.9%) of conjugated equine estrogens (CEEs), or Premarin. It effectively functions as a prodrug to estradiol in this preparation, similarly to E1S. E2S is also formed as a metabolite of estradiol, as well as of estrone and E1S. Aside from its presence in CEEs, E2S is not available as a commercial pharmaceutical drug.
Pharmacokinetics of estradiol
Polyestradiol phosphate is an ester prodrug of estradiol in the form of a polymer which is used via intramuscular injection primarily to treat prostate cancer, but also to treat breast cancer and menopausal symptoms. It has an extremely long duration of action, with a terminal half-life of about 70 days (10 weeks) following a single intramuscular administration of the medication. In addition, unlike most other estradiol esters, the estradiol levels achieved with polyestradiol phosphate are highly constant and uniform. Levels of estradiol in men with intramuscular injections of polyestradiol phosphate once every 4 weeks were about 350 pg/mL with 160 mg, 450 pg/mL with 240 mg, and almost 700 pg/mL with 320 mg, all measured after 6 months of treatment. Polyestradiol phosphate has been discontinued in many countries, and remains available today in only a few countries, mostly the Nordic countries of Europe.