OCPs: A Synopsis
The OCPs are oral contraceptives containing low doses of synthetic estrogens and progestins. These hormones have a direct inhibitory effect on hypothalamic release of gonadotropin releasing hormone (GnRH);. Estrogens inhibit the selection and development of a dominant follicle by suppression of follicle stimulating hormone (FSH);. Progestins inhibit ovulation via suppression of luteinizing hormone (LH); surge. The effects of progestins also include making the cervix hostile to sperm penetration by thickening cervical mucus and preventing implantation through an alteration of endometrial lining.[6]
Virtually all currently available OCPs contain ethinyl estradiol as the synthetic estrogenic compound. Norgestrel, levonorgestrel, norgestimate, and norethindrone are used as synthetic progestins in second-generation pills, and the progestin component in third-generation pills is either desogestrel or gestodene (not available in the United States);. Starting from the late 1960s, the amount of ethinyl estradiol in OCPs was significantly reduced from the initial dose of 150 μg to the current doses of 20 to 35 μg to increase efficacy, safety, and tolerability. Pills containing less than 50 μg of ethinyl estradiol are called “low-dose” OCPs. Most of the low-dose OCPs contain ≤ 35 μg ethinyl estradiol, and the dose of synthetic progestin ranges between 0.1 to 3 mg.[7]
Most synthetic progestins used in OCPs are derived from an altered testosterone molecule, 19-nortestosterone. These progestins vary in their chemical structures, potency, and pharmacokinetics. They bind the androgen receptor with different affinities and show different degrees of androgenicity. In this group, desogestrel, norgestimate, and gestodene are less androgenic compared with levonorgestrel.[8]
Three synthetic progestins with antiandrogenic effects—cyproterone acetate, dienogest, and drospire-none—are used in OCPs.[7] Cyproterone acetate is derived from 17-hydroxyprogesterone, whereas dienogest and drospirenone are derivatives of 19-nortestosterone and 17-α-spirolactone, respectively. Cyproterone acetate is the most potent antiandrogenic progestin. Antiandrogenic potencies of dienogest and drospirenone measured by Hershberger test are ∼40% and 30% of that of cyproterone acetate, respectively.[9] Drospirenone was approved by the U.S. Food and Drug Administration (FDA); in 2000, whereas cyproterone acetate and dienogest containing OCPs are not marketed in the United States.[9]
Semin Reprod Med. 2008;26(1):111-120. © 2008 Thieme Medical Publishers
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