Estradiol enantate
Estradiol enantate, sold under the brand names Perlutal and Topasel among others, is an estrogen medication which is used in hormonal birth control. It is formulated in combination with dihydroxyprogesterone acetophenide (DHPA; algestone acetophenide), a progestin, and is used as a combined injectable contraceptive. Estradiol enantate is not available alone. The medication is given by injection into muscle once a month.
Side effects of estradiol enantate include breast tenderness, breast enlargement, nausea, headache, and fluid retention. The drug is a synthetic estrogen and hence is an agonist of the estrogen receptor (ER), the biological target of estrogens like estradiol. Estradiol enantate is an estrogen ester and a long-lasting prodrug of estradiol in the body. Because of this, it is considered to be a natural and bioidentical form of estrogen.
Estradiol enantate was first described by 1954, and was first studied in combination with DHPA as a combined injectable contraceptive in 1964. The combination was introduced for clinical use by the mid-1970s. Estradiol enantate is not available as a standalone medication (i.e., by itself without DHPA). The combination is available in Latin America and Hong Kong, and was also previously marketed in Spain and Portugal.
Ethinylestradiol
EE is an estrogen similarly to natural estrogens like estradiol and conjugated estrogens (Premarin) and synthetic estrogens like diethylstilbestrol. It binds to and activates both isoforms of the estrogen receptor, ERα and ERβ. In one study, EE was found to have 233% and 38% of the affinity of estradiol for the ERα and ERβ, respectively. In another study, it was found to possess 194% and 151% of the affinity of estradiol for the ERα and ERβ, respectively. EE also appears to signal through the GPER, a membrane estrogen receptor, similarly to estradiol. Estrogens have antigonadotropic effects through activation of the ERα. As a contraceptive, EE acts in concert with a progestin to inhibit the mid-cycle surge in luteinizing hormone (LH) and follicle-stimulating hormone (FSH) via its antigonadotropic effects, thereby inhibiting folliculogenesis and preventing ovulation and hence the possibility of pregnancy.