Gonadal & Ovarian Pharmacology

Correct Answer

C — Tamoxifen

Rationale

Tamoxifen is a selective estrogen receptor modulator (SERM) — a drug that produces tissue-selective estrogen receptor agonist or antagonist effects depending on the target tissue. Letrozole is an aromatase inhibitor. Medroxyprogesterone acetate is a synthetic progestin. Leuprolide acetate is a gonadotropin-releasing hormone agonist.

Correct Answer

A — Drospirenone

Rationale

Drospirenone is derived from spironolactone and is classified as a fourth-generation progestin. Its structural relationship to spironolactone confers anti-androgenic and anti-mineralocorticoid receptor activity. Levonorgestrel and norethindrone are first- and second-generation 19-nortestosterone derivatives. Etonogestrel is a third-generation progestin and the active metabolite of desogestrel.

Correct Answer

B — Levonorgestrel

Rationale

Levonorgestrel is classified as having the highest androgenic index of any commonly used progestin. It is a second-generation 19-nortestosterone derivative with significant androgen receptor binding activity. Drospirenone is anti-androgenic. Medroxyprogesterone acetate has modest glucocorticoid activity and negligible androgenic activity. Etonogestrel is a third-generation progestin with reduced androgenic activity compared to levonorgestrel.

Correct Answer

D — Ethinyl estradiol

Rationale

Ethinyl estradiol is a synthetic estrogen with a chemical modification at the C-17 position that blocks the hepatic enzyme responsible for rapid degradation of natural estradiol, giving it substantially higher oral bioavailability. 17-beta-estradiol is the bioidentical natural estrogen with poor oral bioavailability due to first-pass metabolism. Estriol is the weakest natural estrogen, produced primarily during pregnancy. Conjugated equine estrogens are a mixture of estrogen sulfates extracted from pregnant mares’ urine, not a C-17-modified synthetic.

Correct Answer

A — Micronized progesterone

Rationale

Micronized progesterone (Prometrium) is natural progesterone formulated as very small particles in oil-filled capsules to achieve sufficient oral absorption despite the extensive first-pass hepatic metabolism that prevents unmodified oral progesterone from reaching therapeutic levels. Depot medroxyprogesterone acetate is a synthetic progestin administered by intramuscular injection. Drospirenone is a fourth-generation synthetic progestin. Norethindrone is a first-generation 19-nortestosterone-derived synthetic progestin.

Correct Answer

C — Raloxifene

Rationale

Raloxifene is a selective estrogen receptor modulator that antagonizes the estrogen receptor in both breast tissue and the uterus, distinguishing it from tamoxifen, which acts as a partial agonist at the uterine estrogen receptor. This difference means raloxifene does not carry the endometrial cancer risk associated with tamoxifen. Ospemifene is a selective estrogen receptor modulator that acts as a vaginal agonist and is used for dyspareunia. Ethinyl estradiol is a synthetic estrogen, not a selective estrogen receptor modulator.

Correct Answer

B — Ethinyl estradiol reaches the liver via the portal circulation and stimulates hepatic synthesis of coagulation factors

Rationale

Ethinyl estradiol in combined oral contraceptives is absorbed from the gastrointestinal tract and delivered directly to the liver via the portal circulation at high concentrations. This hepatic first-pass exposure stimulates the liver to synthesize coagulation factors and other proteins including sex hormone-binding globulin, angiotensinogen, and C-reactive protein. The increased coagulation factor production shifts hemostatic balance toward thrombosis. This is why all oral estrogen preparations increase venous thromboembolism risk, and why transdermal estradiol, which bypasses portal first-pass exposure, does not carry this risk.

Correct Answer

D — Transdermal estradiol enters the systemic circulation directly, reaching the liver at physiological concentrations rather than as a concentrated portal bolus

Rationale

When estradiol is applied to the skin as a gel, patch, or spray, it is absorbed directly into the systemic circulation and reaches the liver at normal physiological concentrations. In contrast, oral estradiol is absorbed from the gastrointestinal tract and delivered to the liver via the portal vein at supraphysiological concentrations before it ever reaches the systemic circulation. This concentrated portal exposure is what stimulates hepatic synthesis of coagulation factors and inflammatory proteins. Transdermal delivery eliminates this first-pass hepatic effect, which is why observational data consistently show no increase in venous thromboembolism risk with transdermal estradiol even at higher doses.

Correct Answer

A — Hyperkalemia

Rationale

Drospirenone is derived from spironolactone and retains its anti-mineralocorticoid receptor activity. By blocking the mineralocorticoid receptor in the renal collecting duct, drospirenone reduces aldosterone-driven potassium excretion, promoting potassium retention. When combined with lisinopril, an angiotensin converting enzyme inhibitor that also reduces aldosterone secretion and thereby further reduces renal potassium excretion, additive potassium retention can cause clinically significant hyperkalemia. Serum potassium monitoring is required when drospirenone is used with angiotensin converting enzyme inhibitors, angiotensin receptor blockers, potassium-sparing diuretics, or nonsteroidal anti-inflammatory drugs.

Correct Answer

C — Levonorgestrel competes with testosterone for sex hormone-binding globulin binding, displacing testosterone and increasing the free fraction

Rationale

Ethinyl estradiol potently induces hepatic sex hormone-binding globulin production, which would normally reduce free testosterone by increasing the bound fraction. However, levonorgestrel, as a high-androgenicity 19-nortestosterone-derived progestin, competes with endogenous testosterone for sex hormone-binding globulin binding sites. By occupying sex hormone-binding globulin, levonorgestrel displaces testosterone from the protein, increasing the free (biologically active) testosterone fraction. This is why drospirenone-containing pills, whose progestin does not compete for sex hormone-binding globulin binding, are preferred in women with androgen-excess conditions such as polycystic ovary syndrome and acne.

Correct Answer

B — Micronized progesterone is metabolized to compounds that potentiate the gamma-aminobutyric acid type A receptor, producing sedation

Rationale

Natural progesterone is metabolized in the liver to neuroactive steroids, primarily allopregnanolone, which are positive allosteric modulators of the gamma-aminobutyric acid type A receptor. By enhancing inhibitory gamma-aminobutyric acid signaling, these metabolites produce sedation and anxiolysis. This is a characteristic adverse effect of oral micronized progesterone specifically, because the oral route exposes the liver to progesterone concentrations high enough to produce substantial amounts of these neuroactive metabolites. This effect does not occur with vaginal or intramuscular progesterone preparations, which bypass hepatic first-pass metabolism.

Correct Answer

D — Tamoxifen is converted to endoxifen by CYP2D6 in the liver, and patients who are poor metabolizers achieve lower endoxifen levels and have higher recurrence rates

Rationale

Tamoxifen has low intrinsic estrogen receptor affinity and depends on hepatic conversion to its active metabolite endoxifen for anticancer activity. This conversion is carried out primarily by the cytochrome P450 2D6 enzyme. Patients who carry two non-functional CYP2D6 alleles (poor metabolizers) achieve substantially lower endoxifen levels and have higher breast cancer recurrence rates on tamoxifen than extensive metabolizers. This pharmacokinetic dependency also explains why potent CYP2D6 inhibitors such as paroxetine and fluoxetine are contraindicated in women taking tamoxifen, as they can reduce endoxifen levels by up to 75%.

Correct Answer

A — 9 to 10 months on average after the last injection

Rationale

The average time to return of fertility after discontinuing depot medroxyprogesterone acetate is 9 to 10 months after the last injection, which is substantially longer than for any other reversible contraceptive method. This delay is due to the slow release of medroxyprogesterone acetate from the intramuscular depot and its prolonged suppression of the hypothalamic-pituitary-ovarian axis. Some patients may experience return of ovulation as early as 3 to 4 months, while others may wait longer, but the average is 9 to 10 months. Patients planning a pregnancy in the near term should be counseled about this delay before starting the injection.

Correct Answer

C — Rifampin induces cytochrome P450 3A4, accelerating hepatic metabolism of ethinyl estradiol and progestins and lowering their plasma concentrations

Rationale

Rifampin is the most potent cytochrome P450 3A4 inducer in clinical use. Both ethinyl estradiol and most synthetic progestins are metabolized by CYP3A4. When rifampin induces this enzyme, it dramatically accelerates the hepatic metabolism of these hormones, reducing their plasma concentrations to levels that may be insufficient to maintain anovulation. Even a short course of rifampin produces enzyme induction that persists for approximately 4 weeks after the last dose. No oral, patch, or ring hormonal contraceptive is reliable during rifampin therapy or for 4 weeks after stopping; a copper intrauterine device or barrier method is required as backup.

Correct Answer

A — Ethinyl estradiol induces the enzyme responsible for lamotrigine glucuronidation, accelerating lamotrigine inactivation and lowering its plasma concentration

Rationale

Ethinyl estradiol induces the uridine diphosphate glucuronosyltransferase enzyme responsible for lamotrigine glucuronidation and inactivation. When a woman stabilized on lamotrigine begins a combined oral contraceptive containing ethinyl estradiol, lamotrigine plasma concentrations fall by up to 40 to 65 percent because accelerated glucuronidation increases the rate of lamotrigine clearance. This pharmacokinetic interaction can cause breakthrough seizures. For women with epilepsy stabilized on lamotrigine, progestin-only methods or non-hormonal contraception are preferred, as they contain no ethinyl estradiol and do not alter lamotrigine metabolism.

Correct Answer

C — Removal of ethinyl estradiol eliminates induction of lamotrigine glucuronidation, causing lamotrigine plasma levels to rebound and produce toxicity

Rationale

Ethinyl estradiol induces the uridine diphosphate glucuronosyltransferase enzyme responsible for lamotrigine inactivation. While a woman takes a combined oral contraceptive, this induction accelerates lamotrigine glucuronidation and holds plasma lamotrigine concentrations at a lower steady state. When ethinyl estradiol is withdrawn, the induction resolves within days and lamotrigine clearance slows sharply. Plasma lamotrigine levels rebound, sometimes to two to three times the on-pill level, producing dose-dependent lamotrigine toxicity: dizziness, diplopia, ataxia, and nausea. This rebound toxicity also occurs during the pill-free interval in cyclic regimens. Women stabilized on lamotrigine who stop a combined oral contraceptive must have their lamotrigine dose proactively reduced to prevent toxicity.

Correct Answer

B — Ethinyl estradiol induces hepatic sex hormone-binding globulin production, raising circulating levels and reducing the free testosterone fraction

Rationale

Ethinyl estradiol potently induces hepatic production of sex hormone-binding globulin, raising circulating levels two to four times above baseline. Because testosterone is transported in blood predominantly bound to sex hormone-binding globulin, this increase in the binding protein substantially reduces the free (biologically active) testosterone fraction. With less free testosterone available to stimulate sebaceous glands and androgen-sensitive hair follicles, acne and hirsutism improve. Drospirenone contributes additionally by blocking the androgen receptor directly, and by not competing with testosterone for sex hormone-binding globulin binding as androgenic progestins such as levonorgestrel would.

Correct Answer

D — Tamoxifen acts as a partial estrogen receptor agonist in the uterus, producing endometrial stimulation despite acting as an antagonist in breast tissue

Rationale

Tamoxifen is a selective estrogen receptor modulator whose pharmacological effect is tissue-dependent. In breast tissue, it occupies the estrogen receptor and blocks estradiol-driven proliferation, which is the basis of its anticancer activity. In the uterus, however, the same drug acts as a partial estrogen receptor agonist, stimulating endometrial proliferation. With prolonged use, this uterine agonism produces endometrial hyperplasia and increases the risk of endometrial carcinoma. Abnormal uterine bleeding in a postmenopausal woman on tamoxifen must be investigated promptly for this reason. This tissue-selective difference is what distinguishes tamoxifen from raloxifene, which antagonizes the estrogen receptor in both breast and uterus and does not carry an endometrial cancer risk.