Dr. Pincus

Dr. Gregory Pincus is commonly referred to as the father of the pill. After making national headlines in 1934 by achieving in vitro fertilization of rabbit oocytes, he found that the world was not ready for this technology. He thus shifted his attention from mammalian fertilization to oral contraception for women and received a grant from the Planned Parenthood Federation in 1951 to find a progestin that could be used as an oral contraceptive agent.

After evaluating hundreds of substances, Pincus found two steroid compounds derived from the roots of the wild Mexican yam that could inhibit ovulation in laboratory animals. Pharmaceutical companies refined and advanced these discoveries to extract progestins and estrogens from plant material. Of interest, Pincus and his colleagues devoted a great deal of time and energy to purify the progestin norethynodrel from its estrogen contaminant mestranol. However, they subsequently discovered that mestranol could reduce breakthrough bleeding and acted synergistically with progestins to enhance contraceptive efficacy.

In 1956, Pincus, working in conjunction with the G.D. Searle Pharmaceutical Company and Dr. John Rock, conducted field tests of a hormonal contraceptive pill with hundreds of women in Massachusetts, Puerto Rico, and Haiti. They demonstrated that oral steroid hormones could be effective contraception, with side effects limited primarily to nausea. The U.S. Food and Drug Administration (FDA) authorized the production of contraceptive pills for limited use in 1957. Three years later, the FDA licensed G.D. Searle to produce the first commercially available oral contraceptive, Enovid, which contained 150 μg of mestranol and 9.85mg norethynodrel. Soon after the introduction of Enovid, other manufacturers introduced additional oral contraceptive formulations.

Modern Hormonal Contraceptives

Since the introduction of oral contraceptives more than 40 years ago, the hormone dosage used has been reduced by as much as eightfold. More recently, multiple new estrogens and progestins and several different delivery systems have been utilized in an effort to increase effectiveness, compliance, and continuation rates.

A broad range of contraceptive hormones and delivery systems are presently available in the United States today (Table 26-1). Several of the newer hormonal delivery systems are parenteral, and some of the preparations no longer need to be taken daily. The most frequently used and best studied are the combination oral contraceptives that contain a synthetic estrogen and one of several progestins. Three progestin-only oral contraceptives are currently available. In addition, a vaginal patch, a vaginal ring, a single rod implant, and an injectable medroxyprogesterone are commercially available.

Table 26-1 Formulations of Some Modern Hormonal Contraceptives

Patient Selection

Oral contraceptives are an excellent contraceptive choice for many patients who are willing and able to consistently take a daily pill. In some cases, oral contraceptives may be recommended to patients because of their noncontraceptive benefits, such as treatment of dysmenorrhea or acne. The vast majority of healthy women can take oral contraceptives with an extremely low risk of serious side effects or risks. However, there are several standard contraindications to use of hormonal contraceptive methods that contain estrogen (Table 26-2). Many of these women are good candidates for progestin-only contraceptives. The remainder should be counseled to use an alternative nonhormonal method.

Table 26-2 Contraindications to Use of Combination Oral Contraceptives

Estrogens and Progestins

Estrogens

Combination oral contraceptive pills contain one of two synthetic estrogens: ethinyl estradiol or, less commonly, mestranol. Both of these steroids are created by adding a 17-α ethinyl group to estradiol to increase potency and enhance oral activity by impeding hepatic degradation (Fig. 26-1). Natural estrogens are relatively weak when given by mouth due to their rapid clearance from blood by the liver (i.e., the first-pass effect). As a result of decreased degradation, both of these synthetic estrogens are 10 to 20 times more active than estradiol when given orally, but have similar potency when given intravenously.

Figure 26-1 Synthetic estrogens used in combination oral contraceptives.

The original formulation for oral contraceptive pills contained as much as 150 μg of synthetic estrogen each. When studies found an association between the estrogen content of early oral contraceptives and venous thromboembolism, researchers found that the estrogen component could be significantly reduced with no loss of contraceptive efficacy. As a result, most modern oral contraceptive pills now contain between 25 and 35 μg of ethinyl estradiol, and a few contain as little as 20 μg.⁵ Although reducing the daily estrogen dose to either 30 or 35 μg has been shown to reduce the risk of venous thromboembolism, no study has shown that further decreasing the estrogen dose reduces the risk further.

Progestins

The prototype progestin used in modern oral contraceptive pills is norethindrone (an estrane), which is created from progesterone by adding both a 19-carbon methyl group and a 17-α ethinyl group similar to ethinyl estradiol (Fig. 26-2). Norgestrel (a gonane) is the 18-carbon-ethyl derivative of norethindrone and is a racemic mixture of dextronorgestrel and levonorgestrel. Levonorgestrel is the biologically active component of norgestrel.

Figure 26-2 Progestins used in combination and progestin-only oral contraceptives.

Norethynodrel and ethynodiol diacetate are related progestin analogues with longer durations of action. These progestins have a more potent effect on the endometrium than norethindrone, allowing the daily progestin dose to be reduced to between 0.15 and 1 mg.

In the 1980s, a number of new progestins were developed such as desogestrel and norgestimate. Desogestrel is a “prodrug” and must be metabolized to its active metabolic component, etonogestrel. Norgestimate, although active, is primarily metabolized to norelgestromin and small amounts of levonorgestrel. These progestins maintain desired effects on the endometrium, but had reduced androgenic effects, such as acne, weight gain, and undesired effects on lipids and lipoproteins. Today, the most commonly used progestins in oral contraceptives are norgestimate, norethindrone, and norgestrel. Progestin-only pills with no estrogen component are also discussed in this chapter.

Recently, drospirenone, a somewhat unique progestin, has been introduced in the United States.⁶ This anti-androgenic analogue of spironolactone has a high binding affinity for progesterone and mineralocorticoid receptors, but a low binding affinity for the androgen receptors. Oral contraceptives containing this progestin are associated with less fluid retention but have a slight theoretical risk of hyperkalemia.⁷ Women with renal insufficiency, hepatic dysfunction, or adrenal insufficiency should not use oral contraceptives containing drospirenone.

Mechanism of Action

Oral contraceptives were originally designed such that progestin would inhibit ovulation by suppressing luteinizing hormone release at the level of the hypothalamus or pituitary. Estrogen was included to stabilize the endometrium to minimize breakthrough bleeding and spotting, although estrogen has been found to help suppress ovulation by inhibiting release of follicle-stimulating hormone.

Other contraceptive mechanisms of action of oral contraceptive pills have since been discovered. Progestins decrease entry of sperm into the uterus by decreasing sperm motility and increasing cervical mucus viscosity. Progestins also inhibit sperm transport by decreasing fallopian tube motility. Finally, progestins alter the endometrium and thus inhibit implantation.

Efficacy

Approximately 7% of women using combination oral contraceptives will have an unintended pregnancy during the first 12 months of use.⁸ Rates reported in different clinical trials can be highly variable because of factors, including methodology, demographics, various types of bias, and methods of calculating rates.^9–12 Two of the most common methods are the Pearl index and life table analysis.

The Pearl index is a common method used to compare contraception efficacy. The Pearl index indicates the number of unintentional pregnancies related to 100 women-years of use. To calculate this index, the number of pregnancies that occur during a year are divided by cumulative months of exposure, and the quotient multiplied by 1200. If three pregnancies occur during a year in 100 women, the Pearl index will be 3.0 (i.e., 1200 months × 3 pregnancies/1200). This method is not ideal for comparing rates if studies are of different durations, because pregnancy rates can change over time.

Life table analysis is more effective for comparing failure rates than the Pearl index because a separate failure rate is determined for each month of use.¹² Life table analysis also allows separate evaluation of both method and user failure rates. Method failure rates refer to pregnancy rates that occur when the method has been used correctly, in a consistent manner, and according to the instructions in the package insert. User failure rates (i.e., typical failure rates) refer to pregnancies that occur when the method is not used correctly. The reported method failure rates for oral contraceptive pills are between 1% and 3% and user failure rates are approximately 7%.¹¹ Both method and user failure rates are similar for women over age 30 who are in higher socioeconomic groups. In contrast, the user failure rate is much higher for teenagers and unmarried women, sometimes surpassing 30%.

Decreased Risk of Ectopic Pregnancies

Combination oral contraceptives reduce the risk of ectopic pregnancy by 90%.¹³ The likely mechanism is through suppression of ovulation, an effect that obviously prevents all types of pregnancy. In contrast, some studies have indicated that women using progestin-only oral contraceptives are at higher risk for an ectopic pregnancy than the general population.

Decreased Risk of Pelvic Inflammatory Disease

Several studies have shown that oral contraceptive use reduces the risk of pelvic inflammatory disease (PID) by 50% to 80% compared to women who use no method or a barrier method for contraception.^13–15 However, one recent multi-center study failed to show a protective effect of oral contraceptives.¹⁶

Because oral contraceptives do not protect against the acquisition of lower genital tract sexually transmitted diseases (e.g., Chlamydia trachomatis and Neisseria gonorrhoeae), the assumption is that they impede bacterial ascent from the uterine cervix into the upper genital tract. Several possible mechanisms for this have been suggested. Progestins cause cervical mucus to become thick and viscous, and this might substantially inhibit the ascent of bacteria. Alternatively, the reduced menstrual flow resulting from oral contraceptives could decrease retrograde menstrual flow to the fallopian tubes and result in a less favorable environment for promoting bacterial growth. Finally, hormone-related changes in uterine contractility might make ascent of organisms less likely.

Decreased Risk of Malignancies

Decreased Menstrual Flow and Dysmenorrhea

Up to 75% of young women will experience some degree of dysmenorrhea, and 15% to 20% will have severe pain.^29,30 Multiple studies have shown that combination oral contraceptives reduce both menstrual flow and dysmenorrhea.^29–34

Two possible mechanisms have been proposed to explain how oral contraceptives reduce dysmenorrhea. Women taking oral contraceptives have been shown to have reduced prostaglandins in the menstrual fluid. It is hypothesized that by decreasing prostaglandin production by the uterus, oral contraceptives decrease dysmenorrhea by decreasing either endometrial vasoconstriction and ischemia or uterine contractile activity.^35,36

Decreased Benign Breast Disease

Several studies have shown a 30% to 50% decrease in the incidence of benign fibrocystic breast changes in women using oral contraceptives.^37,38 One of the clearest effects is a decrease in the occurrence of fibroadenomas among current and recent long-term users of oral contraceptives under age 45. The most likely mechanism is through suppression of ovulation and therefore inhibition of the breast cell proliferation that normally occurs in the first half of an ovulatory menstrual cycle.

Ovarian Cysts

Improved Acne

Randomized, placebo-controlled clinical trials have demonstrated that some combination oral contraceptives will reduce acne lesions by as much as 50%.⁴⁴ Several combination oral contraceptives containing new-generation progestins (e.g., norgestimate, desogestrel) or progestational anti-androgens (e.g., drospirenone in the United States, cyproterone acetate overseas) have been shown to be able to effectively reduce acne. Although it is likely that many other pill formulations will reduce acne, most formulations have not been studied for this outcome.

The mechanisms by which oral contraceptives improve acne include elevation of sex hormone-binding globulin, which binds and decreases available testosterone; suppression of the enzyme that converts testosterone to dihydrotestosterone; and suppression of gonadotropins, resulting in decreased levels of ovarian androgens. Pills containing drospirenone also block the action of androgens by acting as an antagonist at the androgen receptors.

Increased Bone Density

The majority of studies indicate that oral contraceptives have a positive effect on bone mineral density, and no studies have demonstrated a negative effect.⁴⁵ Oral contraceptives appear to delay or prevent the decline in bone mass that begins between ages 30 and 40. Women who use oral contraceptives for 5 to 10 years or longer are afforded the greatest protection. A population-based, case-control study revealed a 25% reduction in hip fracture risk in these women.⁴⁶

The positive effects of oral contraceptives on bone mineral density are due primarily to estrogen, which has been demonstrated to increase calcium absorption, decrease calcium loss, and directly decrease bone resorption by inhibiting osteoclast activity. Norethindrone also appears to have a positive effect on bone mass, although the mechanism is uncertain.

Improvement in Rheumatoid Arthritis

Oral contraceptives appear to diminish both the severity and symptomatology of rheumatoid arthritis but do not prevent this disease. A large meta-analysis of nine hospital and population-based studies suggested that oral contraceptives prevent the progression of rheumatoid arthritis to more severe varieties.⁴⁷ However, the protective effect was noted in the hospital- based studies only, suggesting the possibility of some unexplained bias.

Insulin Resistance

The effect of combination oral contraceptives on carbohydrate metabolism has been studied for several decades. It is now recognized that both estrogens and progestins affect glucose metabolism by increasing peripheral resistance to insulin. However, studies of women on current low-estrogen (≤35 μg) formulations have shown minimal changes in glucose and insulin levels that are of no clinical significance.⁴⁸ Further, there is no evidence that combination preparations increase the risk of subsequently developing diabetes in women at risk, such as those with prior gestational diabetes.⁴⁹

Women with polycystic ovary syndrome who usually demonstrate some degree of insulin resistance benefit from oral contraceptives. Although oral contraceptives may slightly increase their insulin resistance, they also reduce associated symptoms such as acne and hirsutism, regulate menses, and protect the endometrium against development of endometrial malignancy.⁵⁰

Insulin-dependent diabetic women can use oral contraceptives with little fear of affecting fasting plasma glucose, insulin requirements, or glycosylated hemoglobin levels.⁵¹ However, one should avoid oral contraceptives in diabetics with evidence of vascular disease because of their increased risk of cardiovascular disease.

Changes in Lipids

The estrogen component of combination oral contraceptives causes elevations in serum triglycerides but has a favorable change on the other two major lipids by elevating high-density lipoprotein cholesterol (HDL-C) while lowering low-density lipoprotein cholesterol (LDL-C) levels.⁵² Contraceptive formulations containing progestins with low or no androgenicity (e.g,. desogestrel, drospirenone, or norgestimate) lower LDL-C and elevate HDL-C and triglycerides. In contrast, contraceptive formulations containing more androgenic progestins may change lipids in an unfavorable direction by lowering HDL-C levels and elevating LDL-C levels.^6,52–54 It is important to be aware of these differences when prescribing oral contraceptives to women with risk factors for cardiovascular disease or to those who have strong family histories of ischemic heart disease or substantial lipid abnormalities.

Coagulation Changes

Low-estrogen (≤35 μg) oral contraception formulations are associated with clinically insignificant changes in both procoagulant and anticoagulant factors.^55,56 However, women with risk factors for venous thromboembolism, such as factor V Leiden mutations, should avoid combination oral contraceptives.

Cardiovascular Risk

The significant areas of concern with oral contraceptives are venous thromboembolism, stroke, and myocardial infarction. However, all of these cardiovascular risks have been dramatically decreased by the significant reduction in estrogen and progestin dosages in modern formulations.