Pharmacokinetics of Exogenous Natural and Synthetic Estrogens and Antiestrogens

Abstract

A. Natural Estrogens In this chapter, the pharmacokinetics of exogenously administered natural estrogens will be described. Natural estrogens considered here include: 17 f3-estradiol as the main-acting estrogen in humans. Esters of 17 f3-estradiol, such as estradiol valerate, estradiol benzoate and estra-diol cypionate. Esterification aims at either better absorption after oral administration or a sustained release from the depot after intramuscular administration. During absorption, the esters are cleaved by endogenous esterases and the pharmacologically active 17 f3-estradiol is released; there-fore, the esters are considered as natural estrogens. Estrone. Estriol. Conjugated equine estrogens, which are not natural estrogens for humans, but, because of their therapeutic use in estrogen replacement therapy, will be treated as natural estrogens.