Hormonal contraceptives inhibit ovulation. Contraceptives typi-cally contain a combination of hormones. For example, ethinyl estradiol may be combined with desogestrel, drospirenone, lev-onorgestrel, norethindrone, norgestimate, or norgestrel. Also, mestranol may be combined with norethindrone. Ethinyl estradiol or ethynodiol diacetate may also be used alone as a contraceptive.
Hormonal contraceptives are absorbed from the GI tract and are widely distributed. They’re metabolized in the kidneys and excret-ed in urine and feces.
Some forms of hormonal contraceptives are available in a trans-dermal patch form. These contraceptives are absorbed through the skin but have the same distribution, metabolism, and excre-tion as orally administered contraceptives.
The primary mechanism of action of combination hormonal con-traceptives (estrogen and progestin) is the suppression of go-nadotropins, which inhibits ovulation. Estrogen suppress-
es secretion of follicle-stimulating hormone, which blocks follicular development and ovulation. Progestin suppress-es the secretion of luteinizing hormone, which prevents ovulation, even if the follicle develops. Progestin also thickens the cervical mucus; this interferes with sperm migration and causes endometrial changes that prevent implantation of a fertilized ovum.
The primary purpose for taking hormonal contraceptives is the prevention of pregnancy in women. The combination of ethinyl estradiol and norgestimate is also used to treat moderate acne in females younger than age 15.
Hormonal contraceptives can interact with other medications in various ways:
§ Antibiotics, oxcarbazepine, phenobarbital, phenytoin, topira-mate, and modafinil may decrease the effectiveness of oral contra-ceptives. A patient taking these drugs with a hormonal contracep-tive needs to use a barrier contraceptive.
§ Atorvastatin may increase serum estrogen levels.
§ Cyclosporin and theophylline have an increased risk of toxicity when taken with hormonal contraceptives.
§ Prednisone increases the therapeutic and possibly toxic effects of hormonal contraceptives. (See Adverse reactions to hormonalcontraceptives.)
§ Several herbal medications can affect serum levels of hormonal contraceptives.