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.
Estrone (medication)
Like estradiol, estrone has poor oral bioavailability. It has been said that, taken by mouth in non-micronized form, a dose of 25 mg estrone is approximately equivalent to 2.5 mg conjugated estrogens, 50 µg ethinylestradiol, or 1 mg diethylstilbestrol in terms of estrogenic potency. Due to its weak oral activity, estrone has been used parenterally instead, for instance by intramuscular injection or vaginal administration. The pharmacokinetics of vaginal estrone have been studied.