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Contraception : Product improvements

Second generation oral contraceptives (utilizing 19 nortestosterone derivatives as the progestin) were characterized by a significant reduction in the estrogenic dosages (usually from 150ug to 50ug or less). This reduction significantly reduced the incidence of thrombotic events without affecting efficacy.

Third generation oral contraceptives were characterized by the addition of newer 19 nortestosterone derived progestins many of which are metabolized to norethindrone,

The common progestins
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The common progestins:
19 nortestosterone derived progestins.
Progestogens, Progesterone antagonists, progesterone, and androgens: synthesis, classification and Uses
Credits: Clinical Obstetrics and Gynecology, 1995; 38: 813-20.

While each progestin derivative has some unique characteristics, it is important to remember that the biologic activity of the progestin of each pill is equal to the dose times the potency of each progestin, which is then counterbalanced by neutralizing effects of estrogen. Some of the original 19 nortestosterone derived progestins had adverse metabolic interactions (lowering HDL and SHBG), when given alone. However, most of these adverse interactions are counterbalanced by the effects of ethinyl estradiol (ie HDL and SHBG increase). Newer combinations have attempted to reduce any potential adverse metabolic changes by using newly formulated progestins (gestodene, norgestimate, and desogestrel) designed to avoid such effects.

Newly formulated progestins
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Newly formulated progestins:
gestodene, norgestimate, and desogestrel.
Progestogens, Progesterone antagonists, progesterone, and androgens: synthesis, classification and Uses
Credits: C. Matthew Peterson, M.D.

These progestins represent the fourth generation of oral contraceptives. When considering these potential adverse effects, it is important to remember that in primate studies the use of oral contraceptives using one of the highest available doses of the most potent 19 nor-progestins still resulted in less atherogenesis than in non-treated monkeys. The take home point is that what may be reported in pharmaceutical literature to promote one contraceptive over another may have no actual clinical relevance because of the combination of the progestin with ethinyl estradiol.

Combination oral contraceptives with the estrogen and progestin components combine to suppress ovulation by inhibiting gonadotropin secretion. Through the activity of the progestin they also: 

  • Inhibit gonadotropin secretion

  • Alter cervical mucus composition

  • Change ovum transport time within the fallopian tube

  • Inhibit implantation by altering the endometrial lining so as to make it unreceptive to successful implantation (decreased gland-to-stromal ratio and decreased overall endometrial thickness)