Megestrol acetate is a synthetic derivative of the naturally occurring steroid hormone, progesterone. Megestrol acetate is a white, crystalline solid chemically designated as 17a( acetyloxy)- 6- methylpregna- 4,6- diene- 3,20- dione. Solubility at 37° C in water is 2 µg per mL, solubility in plasma is 24 µg per mL. Its molecular weight is 384.51. Megestrol acetate is a progesterone, or steroid hormone, that improves appetite in patients with advanced cancer. Megestrol acetate is FDA approved for the palliative treatment of advanced breast and endometrial cancer.
Megestrol acetate is a synthetic progestogen, which differs structurally from progesterone. It shares the actions of other progestational agents: induction of secretory changes in the endometrium, increase in basal body temperature, pituitary inhibition and production of withdrawal bleeding in the presence of estrogen. Additionally, megestrol suppresses ovulation 3and produces anti-gonadotropic and anti-uterotrophic effects. It has slight glucocorticoid activity and a very slight degree of mineralocoricoid activity. Megestrol acetate has no estrogenic, androgenic or anabolic activity. In contrast to progesterone, megestrol acetate is orally active.
Megestrol acetate is used in the palliative management of recurrent, inoperable or metastatic endometrial carcinoma or breast cancer. The drug is also used as an adjunct to surgery or radiation. It has also been used in the management of anorexia, cachexia or an unexplained substantial weight loss. Megestrol aceteate does not replace appropriate methods of treatment of advanced endometrial carcinoma or breast cancer such as surgery or radiation. The drug currently is not recommended for use in other neoplastic diseases, but studies are under way. In the treatment of breast cancer, megestrol has been shown equally effective as tamoxifen, with a similar toxicity profile. It is suggested that, due to its different mechanism of action, megestrol should be considered in women experiencing recurrence of stage I and stage II operable breast cancer, after exposure to antiestrogen therapy.
Like progestins, megestrol acetate induces secretory changes in the endometrium, increases basal body temperature, inhibits pituitary function, and causes withdrawal bleeding in the presence of estrogen. In animals, the drug suppresses ovulation and produces antigonadotrophic, antiuterotrophic, and antiandrogenic/antimyotrophic effects. It has slight glucocorticoid activity but no estrogenic, androgenic, or anabolic activities. Megestrol-induced weight gain is likely related to the drug's appetite stimulant or metabolic effects. Megestrol and/or its metabolites may, either directly or indirectly, stimulate appetite, resulting in weight gain, or may alter metabolic pathways via interference with the production or action of mediators such as cachectin (a hormone that inhibits adipocyte lipogenic enzymes).
The exact mechanism of the anti-neoplastic action of megestrol acetate has not been determined. It has been suggested that the anti-neoplastic effect may result from suppression of luteinizing hormone by inhibition of pituitary function. The precise mechanism for megestrol-induced weight gain has not been clearly established. Evidence from clinical studies indicates that the increase in body weight observed during megestrol therapy is related to the drug¡¦s appetite-stimulant or metabolic effects rather than its glucocorticoid-like effects or the production of edema.