Estradiol is a naturally occurring steroidal estrogen. Estradiol cypionate is produced by esterifying estradiol with cyclopentanepropionic acid, and occurs as a white to practically white, crystalline powder. It is either odorless or may have a slight odor and has a melting range of 149-153°C. Less than 0.1 mg/ml is soluble in water and 25 mg/ml is soluble in alcohol. Estradiol cypionate is sparingly soluble in vegetable oils.
The most active endogenous estrogen, estradiol possesses the pharmacologic profile expected of the estrogen class. Estrogens are necessary for the normal growth and development of the female sex organs and in some species contribute to the development and maintenance of secondary female sex characteristics. Estrogens cause increased cell height and secretions of the cervical mucosa, thickening of the vaginal mucosa, endometrial proliferation and increased uterine tone.
Estrogens have effects on the skeletal system. They increase calcium deposition, accelerate epiphyseal closure and increase bone formation. Estrogens have a slight anabolic effect and can increase sodium and water retention. Estrogens affect the release of gonadotropins from the pituitary gland. This can cause inhibition of lactation, inhibition of ovulation and inhibition of androgen secretion.
In humans, estrogen in oil solutions after IM administration are absorbed promptly and absorption continues over several days. Esterified estrogens (e.g., estradiol cypionate) have delayed absorption after IM administration. Estrogens are distributed throughout the body and accumulate in adipose tissue. Elimination of the steroidal estrogens occurs principally by hepatic metabolism. Estrogens and their metabolites are primarily excreted in the urine, but are also excreted into the bile, where most is reabsorbed from the GI. For mares, indications for the use of estradiol include, induction of estrus during the non-breeding or breeding seasons and to enhance the mare’s uterine defense mechanism. Estradiol cypionate has also been used as an abortifacient agent (see warnings below) in cattle, cats and dogs.