Gonadal & Ovarian Pharmacology

Correct Answer

C — Finasteride

Rationale

Finasteride is classified as a selective type 2 5-alpha-reductase inhibitor. It blocks the type 2 isoform, which is expressed predominantly in the prostate, seminal vesicles, and hair follicles, without substantially inhibiting the type 1 isoform. Dutasteride inhibits both type 1 and type 2 5-alpha-reductase, making it a dual inhibitor rather than a selective type 2 inhibitor. Bicalutamide is a non-steroidal androgen receptor antagonist, not a 5-alpha-reductase inhibitor. Testosterone enanthate is a testosterone ester formulation.

Correct Answer

A — Bicalutamide

Rationale

Bicalutamide is classified as a non-steroidal androgen receptor antagonist. It competitively blocks the androgen receptor with no intrinsic agonist activity and has no steroidal backbone. Finasteride is a 5-alpha-reductase inhibitor, not an androgen receptor antagonist. Spironolactone is a steroidal agent classified as an aldosterone antagonist that also has anti-androgenic properties; it is not classified as a non-steroidal androgen receptor antagonist. Testosterone is an androgen, not an antagonist.

Correct Answer

D — Enzalutamide

Rationale

Enzalutamide is classified as a second-generation androgen receptor antagonist. It has approximately 5 to 8 times greater androgen receptor affinity than bicalutamide and additionally inhibits nuclear translocation of the androgen receptor complex and its deoxyribonucleic acid binding — a more complete mechanism of androgen receptor pathway suppression than first-generation agents. Bicalutamide is a first-generation non-steroidal androgen receptor antagonist. Finasteride is a 5-alpha-reductase inhibitor. Leuprolide acetate is a gonadotropin-releasing hormone agonist.

Correct Answer

B — Testosterone enanthate

Rationale

Testosterone enanthate is classified as an intramuscular depot testosterone ester. It is injected into muscle and releases testosterone gradually from the injection site over 1 to 2 weeks. Testosterone cypionate is the other commonly used intramuscular ester with a similar profile. Transdermal testosterone gel is absorbed through the skin. Oral testosterone undecanoate is absorbed via the intestinal lymphatic system. Subcutaneous testosterone pellets are implanted under the skin every 3 to 6 months.

Correct Answer

A — Dutasteride

Rationale

Dutasteride inhibits both type 1 and type 2 isoforms of 5-alpha-reductase, achieving greater overall dihydrotestosterone suppression (approximately 90 to 95%) than finasteride, which selectively inhibits only the type 2 isoform (approximately 70% dihydrotestosterone suppression). This dual inhibition is the defining classification distinction between dutasteride and finasteride. Bicalutamide is a non-steroidal androgen receptor antagonist. Spironolactone is an aldosterone antagonist with anti-androgenic properties, not a 5-alpha-reductase inhibitor.

Correct Answer

C — Spironolactone

Rationale

Spironolactone is classified as an aldosterone antagonist (mineralocorticoid receptor antagonist). It competitively blocks the mineralocorticoid receptor in the renal collecting duct, reducing aldosterone-driven sodium reabsorption and potassium excretion. At higher clinical doses it also blocks the androgen receptor, producing anti-androgenic effects used therapeutically in polycystic ovary syndrome and hirsutism. Finasteride is a 5-alpha-reductase inhibitor. Testosterone enanthate is a testosterone ester. Bicalutamide is a non-steroidal androgen receptor antagonist.

Correct Answer

B — 5-alpha-reductase converts testosterone to dihydrotestosterone in prostate, scalp, and skin, where dihydrotestosterone is the dominant androgen; muscle and bone are maintained primarily by testosterone itself, which finasteride does not reduce

Rationale

The tissue selectivity of 5-alpha-reductase inhibitors reflects the tissue distribution of the enzyme itself. 5-alpha-reductase is expressed at high levels in the prostate, seminal vesicles, hair follicles, and external genital skin, where it converts testosterone to dihydrotestosterone intracellularly. Dihydrotestosterone binds the androgen receptor with approximately 3 to 5 times greater affinity than testosterone and drives tissue-specific effects including prostate growth and male-pattern hair loss. Skeletal muscle, bone, erythropoiesis, and libido are maintained primarily by testosterone acting directly on the androgen receptor, without requiring conversion to dihydrotestosterone. Finasteride blocks the conversion step selectively in tissues that express type 2 5-alpha-reductase, reducing dihydrotestosterone-mediated effects there while leaving testosterone concentrations and testosterone-mediated effects intact.

Correct Answer

D — Type 2 5-alpha-reductase is expressed predominantly in the prostate and is responsible for the majority of intraprostatic dihydrotestosterone production; blocking this isoform substantially reduces the androgen-driven prostate growth that produces obstructive symptoms

Rationale

The two 5-alpha-reductase isoforms have distinct tissue distributions. Type 2 is expressed predominantly in the prostate, seminal vesicles, and hair follicles and is responsible for the majority of intraprostatic dihydrotestosterone synthesis. Type 1 is expressed in skin, sebaceous glands, and liver. Because prostatic dihydrotestosterone production depends primarily on type 2, finasteride’s selective type 2 inhibition is sufficient to substantially reduce intraprostatic dihydrotestosterone, shrink prostate volume, improve urinary flow, and reduce the risk of acute urinary retention and surgery. Dutasteride achieves greater overall dihydrotestosterone suppression by adding type 1 inhibition, but this additional suppression does not meaningfully improve benign prostatic hyperplasia outcomes compared to finasteride in head-to-head trials.

Correct Answer

A — Approximately 4.0 ng/mL, because finasteride reduces prostate-specific antigen by approximately 50% through a pharmacodynamic effect on prostate-specific antigen gene transcription, so the measured value must be doubled

Rationale

Finasteride and dutasteride both reduce prostate-specific antigen by approximately 50% within 3 to 6 months of starting therapy. This is a pharmacodynamic effect: dihydrotestosterone drives transcription of the prostate-specific antigen gene, and blocking dihydrotestosterone production with a 5-alpha-reductase inhibitor reduces prostate-specific antigen output from prostatic epithelium. Because the measured value reflects this suppression, the clinician must double the measured prostate-specific antigen to estimate what the true level would be without the drug. A measured value of 2.0 ng/mL in a patient on finasteride represents an estimated true value of approximately 4.0 ng/mL. Failure to apply this correction means clinically significant prostate-specific antigen elevations can be missed. Any upward trend in measured prostate-specific antigen despite 5-alpha-reductase inhibitor therapy also warrants investigation regardless of the absolute number.

Correct Answer

C — Testosterone activates androgen receptors in bone marrow erythroid progenitor cells and upregulates erythropoietin production, increasing red blood cell synthesis and raising hematocrit

Rationale

Erythrocytosis is the most common dose-dependent adverse effect of testosterone replacement therapy. Testosterone stimulates erythropoiesis through two complementary mechanisms: direct activation of androgen receptors on bone marrow erythroid progenitor cells, which promotes red blood cell differentiation; and upregulation of renal erythropoietin production, which amplifies the erythroid stimulus systemically. The combined effect raises hematocrit. This risk is greatest with injectable testosterone formulations such as enanthate and cypionate, which produce supraphysiological peak concentrations every 1 to 2 weeks. Elevated hematocrit increases blood viscosity and raises the risk of venous thromboembolism and arterial events. Hematocrit monitoring at 3 months and annually is required for all patients on testosterone replacement therapy.

Correct Answer

B — Bicalutamide blocks androgen receptor signaling in the hypothalamus and pituitary, removing negative feedback on luteinizing hormone secretion and driving a compensatory increase in endogenous testosterone production

Rationale

Bicalutamide blocks the androgen receptor throughout the body, including in the hypothalamus and pituitary gland. Under normal circumstances, testosterone and dihydrotestosterone exert negative feedback on luteinizing hormone secretion through these androgen receptors. When bicalutamide occupies and blocks these receptors, the feedback signal is lost — the hypothalamic-pituitary axis can no longer sense circulating androgens — and luteinizing hormone secretion rises substantially. Elevated luteinizing hormone then drives Leydig cell testosterone production up by approximately 1.5-fold above baseline. This compensatory testosterone rise partially offsets bicalutamide’s peripheral androgen receptor blockade in target tissues, which is why bicalutamide monotherapy is generally combined with a gonadotropin-releasing hormone agonist or antagonist in prostate cancer treatment to suppress this testosterone rebound.

Correct Answer

D — Enzalutamide acts as a negative allosteric modulator of gamma-aminobutyric acid type A receptors in the central nervous system, reducing inhibitory neurotransmission and lowering the seizure threshold

Rationale

Enzalutamide has a distinctive central nervous system adverse effect — seizure risk of approximately 0.5% per year — that is not shared by bicalutamide or other anti-androgens. The mechanism is negative allosteric modulation of gamma-aminobutyric acid type A receptors. Gamma-aminobutyric acid type A receptors mediate the primary inhibitory tone in the central nervous system; reducing their function lowers the seizure threshold. This property is unrelated to enzalutamide’s androgen receptor antagonism and is an off-target effect of the drug’s structure. Enzalutamide is used with caution in patients with a prior seizure history or other risk factors for seizure. The drug also causes more prominent fatigue and cognitive impairment than bicalutamide, likely reflecting broader central nervous system effects.

Correct Answer

A — Exogenous testosterone suppresses the hypothalamic-pituitary-gonadal axis through negative feedback, reducing gonadotropin secretion and the intratesticular testosterone required for spermatogenesis; human chorionic gonadotropin preserves spermatogenesis by maintaining intratesticular testosterone via luteinizing hormone receptor stimulation without suppressing the axis

Rationale

Testosterone replacement therapy suppresses spermatogenesis by providing supraphysiological androgen levels to the systemic circulation, which feeds back on the hypothalamus and pituitary to reduce gonadotropin-releasing hormone pulsatility and luteinizing hormone secretion. The resulting fall in luteinizing hormone reduces intratesticular testosterone, which must be maintained at concentrations far higher than systemic levels to sustain spermatogenesis. Most men develop profound oligospermia or azoospermia within 3 to 6 months. For hypogonadal men who wish to preserve fertility, human chorionic gonadotropin provides the luteinizing hormone receptor stimulus needed to maintain intratesticular testosterone without suppressing hypothalamic-pituitary-gonadal axis function, allowing both testosterone-deficiency symptoms and spermatogenesis to be addressed simultaneously.

Correct Answer

C — Oral anabolic-androgenic steroids require C17-alpha-alkylation to resist first-pass hepatic degradation; this chemical modification blocks the hepatic oxidation pathway, causing the steroid to accumulate in hepatocytes and impair bile acid transport, leading to cholestasis and hepatocellular injury

Rationale

Natural testosterone is rapidly metabolized at the C17-beta hydroxyl position by hepatic enzymes and cleared. Oral anabolic-androgenic steroids such as stanozolol, oxandrolone, and oxymetholone require a C17-alpha methyl group to resist this hepatic degradation, allowing sufficient oral bioavailability. However, this modification also blocks the liver’s normal mechanism for conjugating and excreting the steroid. The drug accumulates in hepatocytes, impairs bile acid transporter function, and produces intrahepatic cholestasis. With prolonged use, this progresses to peliosis hepatis (blood-filled hepatic cysts), and eventually hepatocellular adenoma or carcinoma. Injectable anabolic-androgenic steroids such as nandrolone decanoate use an ester linkage at the C17 position that undergoes normal cleavage and hepatic metabolism after absorption from the intramuscular depot, generating the parent steroid without the blocking modification. The route of administration and the C17 chemistry together determine hepatotoxic risk.

Correct Answer

A — Finasteride reduces prostate-specific antigen by approximately 50% through suppression of dihydrotestosterone-driven gene transcription; an upward trend from the nadir while on therapy signals a failure of this suppression, which can indicate prostate cancer producing prostate-specific antigen independently of dihydrotestosterone, and the estimated true value at 2.1 ng/mL measured is approximately 4.2 ng/mL

Rationale

Finasteride reduces prostate-specific antigen by approximately 50% within 3 to 6 months through a pharmacodynamic effect: dihydrotestosterone drives transcription of the prostate-specific antigen gene, and blocking dihydrotestosterone production reduces glandular prostate-specific antigen output. Once a new steady-state nadir is established — in this case 1.4 ng/mL at 6 months — the prostate-specific antigen value is expected to remain stable or fall further on continued therapy. A rising prostate-specific antigen despite ongoing 5-alpha-reductase inhibition signals that something is overriding the drug’s suppressive effect. Prostate cancer cells that have lost androgen-dependent prostate-specific antigen regulation can produce rising prostate-specific antigen despite low dihydrotestosterone. Applying the doubling correction, a measured 2.1 ng/mL corresponds to an estimated true value of approximately 4.2 ng/mL — above the standard screening threshold. Any upward trend on therapy requires investigation regardless of the absolute measured value.

Correct Answer

C — Supraphysiological testosterone concentrations substantially increase aromatization to estradiol in peripheral adipose and muscle tissue; the resulting elevation in circulating estradiol stimulates estrogen receptor alpha in breast glandular tissue, producing gynecomastia

Rationale

A significant fraction of circulating testosterone undergoes peripheral aromatization to estradiol via the aromatase enzyme in adipose tissue, muscle, and other sites. At physiological testosterone levels, the resulting estradiol is within the normal male range and does not produce breast effects. At supraphysiological testosterone concentrations used in non-medical performance enhancement, the mass action of aromatase on the greatly elevated androgen substrate drives estradiol production substantially above normal male levels. Elevated circulating estradiol then acts on estrogen receptor alpha in breast glandular tissue, stimulating ductal and glandular proliferation and producing gynecomastia. The breast tissue cannot distinguish whether the estradiol arrived from physiological sources or from supraphysiological androgen aromatization — the estrogenic stimulus is the same.

Correct Answer

B — A small volume of the castor oil vehicle in which testosterone undecanoate is formulated has entered the systemic venous circulation and embolized to the pulmonary vasculature, producing pulmonary oil microembolism

Rationale

Testosterone undecanoate (Nebido) is formulated in castor oil as the vehicle for its intramuscular depot delivery. If a small amount of this oil vehicle is inadvertently injected into a venous structure rather than muscle, it can enter the systemic venous circulation and embolize to the pulmonary vasculature. This pulmonary oil microembolism produces symptoms within minutes of injection — cough, dyspnea, and chest pain — as the oil droplets temporarily obstruct small pulmonary vessels and trigger a pulmonary vascular response. The event can progress to syncope and cardiovascular compromise in severe cases. Because this risk is specific to the large-volume oil vehicle used in testosterone undecanoate long-acting injectable preparations, all Nebido injections must be administered by a healthcare professional with a mandatory 30-minute post-injection observation period. This requirement does not apply to testosterone enanthate or cypionate, which use smaller injection volumes and different vehicles.

Correct Answer

D — Dihydrotestosterone is required for normal male external genital virilization during fetal development; finasteride blocks dihydrotestosterone production and exposure of a male fetus during this window causes feminization of the external genitalia

Rationale

During male fetal development, dihydrotestosterone produced by the type 2 5-alpha-reductase in fetal external genital tissue is required for virilization: fusion of the labioscrotal folds into the scrotum, development of the penis and penile urethra, and descent of the testes. Testosterone alone is insufficient for this external genital virilization because the relevant target cells primarily express 5-alpha-reductase and depend on local dihydrotestosterone. If a pregnant woman is exposed to finasteride during the window of male external genital development, the drug suppresses fetal dihydrotestosterone production, causing a male fetus to develop feminized or ambiguous external genitalia. Finasteride is therefore absolutely contraindicated in women who are pregnant or may become pregnant. Women of childbearing potential taking finasteride must use effective contraception, and must not handle crushed or broken tablets, as the drug can be absorbed through skin.