GnRH Analogs: Mechanisms, Formulations, and Clinical Applications — Questions

Drug Classification · Questions 1–6

Identify the pharmacological class or categorical label for each drug. Vocabulary preparation is sufficient to answer every question in this section.

Question 1

Which of the following drugs is classified as a gonadotropin-releasing hormone receptor antagonist?

A)Degarelix
B)Leuprolide
C)Triptorelin
D)Goserelin

Correct Answer

A) Degarelix

Rationale

Degarelix is a gonadotropin-releasing hormone receptor antagonist: it competitively blocks the receptor without any initial activation, producing immediate testosterone suppression without a testosterone flare. Leuprolide, triptorelin, and goserelin are all gonadotropin-releasing hormone agonist analogs that initially activate the receptor before producing downregulation-mediated suppression.

Question 2

Which of the following gonadotropin-releasing hormone agonist depot formulations is administered as a biodegradable rod-shaped implant placed subcutaneously?

A)Leuprolide acetate microsphere (Lupron Depot)
B)Triptorelin microsphere (Trelstar)
C)Goserelin acetate implant (Zoladex)
D)Leuprolide acetate atrigel (Eligard)

Correct Answer

C) Goserelin acetate implant (Zoladex)

Rationale

Goserelin acetate (Zoladex) is formulated as a rod-shaped biodegradable implant placed subcutaneously in the anterior abdominal wall using a trocar device; no mixing or reconstitution is required. Leuprolide microsphere (Lupron Depot) and triptorelin microsphere (Trelstar) are intramuscular microsphere depot formulations. Leuprolide atrigel (Eligard) is a subcutaneous gel-forming formulation, but it is not a preformed rod-shaped implant.

Question 3

Which of the following correctly classifies relugolix according to its primary drug transporter substrate profile?

A)Cytochrome P450 3A4 substrate with negligible transporter involvement
B)P-glycoprotein and breast cancer resistance protein substrate
C)Organic anion-transporting polypeptide 1B1 substrate with P-glycoprotein inhibition
D)Cytochrome P450 2C8 substrate with organic anion-transporting polypeptide inhibition

Correct Answer

B) P-glycoprotein and breast cancer resistance protein substrate

Rationale

Relugolix is a substrate of P-glycoprotein and breast cancer resistance protein. Strong P-glycoprotein inhibitors such as amiodarone, clarithromycin, itraconazole, and verapamil can increase relugolix exposure up to fourfold. Relugolix is not significantly metabolized by cytochrome P450 3A4, which distinguishes its drug interaction profile from elagolix. Organic anion-transporting polypeptide 1B1 and cytochrome P450 2C8 involvement describes elagolix, not relugolix.

Question 4

Which of the following correctly identifies the primary metabolic pathway for elagolix?

A)P-glycoprotein efflux with minimal hepatic metabolism
B)Renal elimination with no significant cytochrome P450 involvement
C)Cytochrome P450 2D6 hydroxylation as the primary pathway
D)Cytochrome P450 3A4 metabolism as the primary pathway, with secondary contribution from cytochrome P450 2C8

Correct Answer

D) Cytochrome P450 3A4 metabolism as the primary pathway, with secondary contribution from cytochrome P450 2C8

Rationale

Elagolix is metabolized primarily by cytochrome P450 3A4, with secondary contribution from cytochrome P450 2C8. This makes it susceptible to interactions with strong cytochrome P450 3A4 inhibitors (ketoconazole, ritonavir, clarithromycin), which substantially increase elagolix exposure; the 200-milligram twice-daily dose is contraindicated with these agents. Strong cytochrome P450 3A4 inducers such as rifampin reduce elagolix plasma concentrations and may impair efficacy. P-glycoprotein substrate classification applies to relugolix, not elagolix.

Question 5

Which of the following drugs is classified as a non-steroidal anti-androgen used to prevent the testosterone flare associated with initiation of a gonadotropin-releasing hormone agonist depot?

A)Bicalutamide
B)Degarelix
C)Bromocriptine
D)Octreotide

Correct Answer

A) Bicalutamide

Rationale

Bicalutamide is a non-steroidal anti-androgen that blocks androgen receptors in target tissues. It is co-administered beginning 7 to 14 days before the first gonadotropin-releasing hormone agonist depot injection and continued for 4 weeks to prevent symptomatic testosterone flare in at-risk prostate cancer patients. Degarelix is a gonadotropin-releasing hormone antagonist that avoids the flare by a different mechanism. Bromocriptine is a dopamine agonist and octreotide is a somatostatin analog; neither has anti-androgen activity.

Question 6

Which of the following correctly classifies triptorelin according to its pharmacological class and depot formulation type?

A)Gonadotropin-releasing hormone antagonist administered as subcutaneous implant
B)Gonadotropin-releasing hormone antagonist administered as oral tablet
C)Gonadotropin-releasing hormone agonist administered as intramuscular microsphere depot
D)Gonadotropin-releasing hormone agonist administered as subcutaneous autogel

Correct Answer

C) Gonadotropin-releasing hormone agonist administered as intramuscular microsphere depot

Rationale

Triptorelin (Trelstar) is a gonadotropin-releasing hormone agonist analog administered as an intramuscular microsphere depot in 1-month, 3-month, and 6-month formulations. It is not a gonadotropin-releasing hormone antagonist. The subcutaneous implant description applies to goserelin. The subcutaneous autogel description applies to lanreotide, a somatostatin analog. Oral formulation applies to the non-peptide antagonists elagolix and relugolix.

Core Pharmacology · Questions 7–14

Apply your understanding of drug mechanisms, pharmacokinetics, and drug interactions. Each question requires one reasoning step.

Question 7

A patient with prostate cancer and vertebral metastases requires androgen deprivation therapy. His oncologist selects degarelix rather than leuprolide to avoid the risk of clinical flare. Which of the following best explains why degarelix does not produce an initial testosterone surge?

A)Degarelix directly inhibits testosterone biosynthesis in Leydig cells before acting at the pituitary level
B)Degarelix competitively blocks the gonadotropin-releasing hormone receptor without activating it, preventing the initial luteinizing hormone surge that drives testosterone production
C)Degarelix is a partial gonadotropin-releasing hormone receptor agonist that produces submaximal luteinizing hormone secretion insufficient to raise testosterone above baseline
D)Degarelix suppresses gonadotropin-releasing hormone secretion from hypothalamic neurons, eliminating the pituitary stimulus for luteinizing hormone release

Correct Answer

B) Degarelix competitively blocks the gonadotropin-releasing hormone receptor without activating it, preventing the initial luteinizing hormone surge that drives testosterone production

Rationale

Degarelix is a competitive gonadotropin-releasing hormone receptor antagonist. Unlike gonadotropin-releasing hormone agonist analogs, which initially activate the receptor and trigger a surge of luteinizing hormone and follicle-stimulating hormone before receptor downregulation occurs, degarelix occupies the receptor without any Gq-mediated activation. No initial luteinizing hormone surge is produced, testosterone does not rise, and castrate levels are achieved within 3 days. Degarelix does not act directly on Leydig cells, is not a partial agonist, and does not act at the hypothalamic level to suppress gonadotropin-releasing hormone neurons.

Question 8

A patient with endometriosis-associated pain is being considered for elagolix therapy. Her physician explains that elagolix offers a clinical advantage over depot gonadotropin-releasing hormone agonists because of dose-dependent suppression. Which of the following best describes this pharmacodynamic distinction?

A)Elagolix produces complete estradiol suppression equivalent to surgical menopause at all approved doses, but with a shorter duration of action than depot agonists
B)Elagolix has no effect on bone mineral density at any approved dose because it preserves residual follicle-stimulating hormone activity
C)Elagolix suppresses luteinizing hormone but not follicle-stimulating hormone, allowing partial ovarian function to be maintained regardless of dose
D)The 150-milligram once-daily dose produces partial estradiol suppression preserving some ovarian function, while the 200-milligram twice-daily dose produces near-complete suppression; this titratable effect is not achievable with depot gonadotropin-releasing hormone agonists

Correct Answer

D) The 150-milligram once-daily dose produces partial estradiol suppression preserving some ovarian function, while the 200-milligram twice-daily dose produces near-complete suppression; this titratable effect is not achievable with depot gonadotropin-releasing hormone agonists

Rationale

Elagolix achieves titratable hypothalamic-pituitary-gonadal axis suppression based on dose. The 150-milligram once-daily dose suppresses estradiol to early follicular phase levels — partial suppression that reduces pain while preserving some ovarian function and limiting bone mineral density loss. The 200-milligram twice-daily dose produces near-complete estradiol suppression equivalent to surgical menopause, with superior pain control but greater bone mineral density loss. Depot gonadotropin-releasing hormone agonists invariably produce profound, non-titratable suppression. Elagolix does affect bone mineral density in a dose-dependent manner, and it suppresses both luteinizing hormone and follicle-stimulating hormone.

Question 9

A patient with prostate cancer is taking relugolix for androgen deprivation therapy. His cardiologist starts amiodarone for atrial fibrillation. Which of the following best explains the pharmacokinetic interaction between these two drugs?

A)Amiodarone inhibits P-glycoprotein, reducing efflux transport of relugolix from intestinal and hepatic cells, increasing relugolix plasma concentrations up to fourfold and potentially causing excessive testosterone suppression
B)Amiodarone induces cytochrome P450 3A4, accelerating relugolix metabolism and reducing plasma concentrations, risking inadequate testosterone suppression
C)Amiodarone displaces relugolix from plasma protein binding sites, transiently increasing free relugolix concentration but without sustained effect on testosterone levels
D)Amiodarone inhibits organic anion-transporting polypeptide 1B1, reducing hepatic uptake of relugolix and producing the same interaction as seen with elagolix and cyclosporine

Correct Answer

A) Amiodarone inhibits P-glycoprotein, reducing efflux transport of relugolix from intestinal and hepatic cells, increasing relugolix plasma concentrations up to fourfold and potentially causing excessive testosterone suppression

Rationale

Relugolix is a substrate of P-glycoprotein and breast cancer resistance protein. Amiodarone is a potent P-glycoprotein inhibitor. Inhibition of P-glycoprotein reduces efflux transport of relugolix from enterocytes and hepatocytes, markedly increasing relugolix bioavailability and plasma concentrations — up to fourfold by pharmacokinetic modeling. This combination is contraindicated or requires dose reduction. Amiodarone does not induce cytochrome P450 3A4 (it is primarily a cytochrome P450 inhibitor). The organic anion-transporting polypeptide 1B1 interaction describes elagolix and cyclosporine, not relugolix.

Question 10

A 72-year-old man with prostate cancer on a depot gonadotropin-releasing hormone agonist is found to have a corrected QT interval of 480 milliseconds on routine electrocardiogram. His other medications include haloperidol for behavioral symptoms. Which of the following best explains the mechanism by which androgen deprivation therapy contributes to QT prolongation?

A)Gonadotropin-releasing hormone agonist binding to cardiac L-type calcium channels directly prolongs phase 2 of the action potential
B)Suppression of testosterone by androgen deprivation therapy reduces the expression of cardiac repolarizing potassium channels, prolonging the action potential duration and increasing the corrected QT interval
C)Androgen deprivation therapy raises estrogen levels relative to testosterone, and estrogen directly blocks cardiac sodium channels
D)Androgen deprivation therapy causes hypokalemia through renal potassium wasting, and hypokalemia secondarily prolongs the QT interval

Correct Answer

B) Suppression of testosterone by androgen deprivation therapy reduces the expression of cardiac repolarizing potassium channels, prolonging the action potential duration and increasing the corrected QT interval

Rationale

Testosterone has a direct facilitatory effect on cardiac repolarizing potassium channel expression. Testosterone suppression during androgen deprivation therapy reduces these channels, prolonging the cardiac action potential duration and increasing the corrected QT interval by approximately 10 to 20 milliseconds on average. When combined with other QT-prolonging agents such as haloperidol, the risk of clinically significant QT prolongation is substantially amplified. Gonadotropin-releasing hormone agonists do not directly bind cardiac calcium channels, estrogen-mediated sodium channel blockade is not the primary mechanism, and androgen deprivation therapy does not cause renal potassium wasting.

Question 11

A woman taking elagolix 200 milligrams twice daily for endometriosis is started on rifampin for tuberculosis. After 4 weeks, her dysmenorrhea and pelvic pain return despite continued elagolix. Which of the following best explains the loss of efficacy?

A)Rifampin competes with elagolix for binding at the gonadotropin-releasing hormone receptor, reducing receptor occupancy and allowing estradiol levels to rise
B)Rifampin is a potent cytochrome P450 3A4 inducer; increased cytochrome P450 3A4 activity substantially accelerates elagolix metabolism, lowering plasma elagolix concentrations and reducing hypothalamic-pituitary-gonadal axis suppression
C)Rifampin inhibits P-glycoprotein transport of elagolix in the intestine, paradoxically reducing elagolix absorption and systemic exposure
D)Rifampin activates hepatic glucuronidation of elagolix, producing an active metabolite that blocks elagolix binding at the gonadotropin-releasing hormone receptor

Correct Answer

B) Rifampin is a potent cytochrome P450 3A4 inducer; increased cytochrome P450 3A4 activity substantially accelerates elagolix metabolism, lowering plasma elagolix concentrations and reducing hypothalamic-pituitary-gonadal axis suppression

Rationale

Elagolix is metabolized primarily by cytochrome P450 3A4. Rifampin is one of the most potent inducers of cytochrome P450 3A4 available clinically. Induction of cytochrome P450 3A4 substantially increases the rate of elagolix metabolism, reducing plasma concentrations and diminishing hypothalamic-pituitary-gonadal axis suppression — allowing estradiol to rise and endometriosis symptoms to return. Rifampin does not compete at the gonadotropin-releasing hormone receptor. Rifampin is a P-glycoprotein inducer (not inhibitor), but this is not the primary mechanism for elagolix. Elagolix does not produce an active receptor-blocking metabolite.

Question 12

A 24-year-old man with Kallmann syndrome and hypogonadotropic hypogonadism desires fertility. He has prepubertal-range testosterone and undetectable luteinizing hormone and follicle-stimulating hormone despite an anatomically intact pituitary on imaging. Which of the following best explains why pulsatile gonadotropin-releasing hormone pump therapy successfully restores spermatogenesis in this patient?

A)Continuous subcutaneous infusion of gonadotropin-releasing hormone downregulates pituitary gonadotropin-releasing hormone receptors, creating a paradoxical increase in gonadotropin secretion
B)Pulsatile gonadotropin-releasing hormone delivery mimics the physiological hypothalamic secretory pattern, maintaining gonadotropin-releasing hormone receptor responsiveness and restoring pulsatile luteinizing hormone and follicle-stimulating hormone secretion from an intact pituitary
C)Pulsatile gonadotropin-releasing hormone bypasses the pituitary entirely and directly stimulates Leydig cell testosterone synthesis and Sertoli cell support of spermatogenesis
D)Pulsatile gonadotropin-releasing hormone suppresses hypothalamic kisspeptin neurons, releasing the pituitary from inhibitory control and restoring autonomous gonadotropin secretion

Correct Answer

B) Pulsatile gonadotropin-releasing hormone delivered at physiological intervals maintains gonadotropin-releasing hormone receptor sensitivity, restoring pulsatile luteinizing hormone and follicle-stimulating hormone secretion from the intact pituitary and supporting natural follicular development

Rationale

In Kallmann syndrome and normosmic idiopathic hypogonadotropic hypogonadism, the defect is absent or insufficient pulsatile gonadotropin-releasing hormone secretion from the hypothalamus. The pituitary gonadotrophs are structurally intact and retain their ability to respond to gonadotropin-releasing hormone. Pulsatile pump therapy delivers gonadotropin-releasing hormone at physiological intervals of 60 to 120 minutes, maintaining receptor sensitivity and driving pulsatile luteinizing hormone and follicle-stimulating hormone secretion. This restores the gonadal stimulus for spermatogenesis, achieving adequate sperm counts in approximately 75 to 80% of treated men. Continuous delivery would cause receptor downregulation and suppress gonadotropins. Gonadotropin-releasing hormone does not act directly on Leydig cells or suppress kisspeptin neurons as its primary therapeutic mechanism here.

Question 13

A man with prostate cancer has been on continuous androgen deprivation therapy for 18 months. Dual-energy X-ray absorptiometry shows a lumbar spine T-score decline from negative 0.5 to negative 1.8. Which of the following best explains the mechanism of bone mineral density loss during androgen deprivation therapy?

A)Testosterone normally suppresses RANK ligand expression on osteoblasts and directly promotes osteoblast differentiation; testosterone suppression by androgen deprivation therapy removes this anabolic and anti-resorptive effect, increasing osteoclast-mediated bone resorption relative to bone formation
B)Gonadotropin-releasing hormone agonist binding to bone cell receptors directly activates osteoclast differentiation through a Gq-mediated signaling pathway independent of testosterone suppression
C)Androgen deprivation therapy raises parathyroid hormone secretion by reducing calcium absorption, and secondary hyperparathyroidism drives bone resorption
D)Testosterone suppression reduces erythropoietin levels, causing anemia that impairs osteoblast oxygen delivery and reduces new bone formation

Correct Answer

A) Testosterone normally suppresses RANK ligand expression on osteoblasts and directly promotes osteoblast differentiation; testosterone suppression by androgen deprivation therapy removes this anabolic and anti-resorptive effect, increasing osteoclast-mediated bone resorption relative to bone formation

Rationale

Testosterone exerts direct anabolic effects on bone by promoting osteoblast differentiation and function, and indirectly suppresses bone resorption by reducing RANK ligand expression. Testosterone is also aromatized peripherally to estradiol, which provides additional anti-resorptive protection in men. Androgen deprivation therapy removes both the direct androgenic and indirect estrogenic bone-protective effects, shifting the bone remodeling balance toward net resorption. Bone mineral density declines approximately 2 to 3% per year at the lumbar spine and femoral neck. The drug itself does not act directly on bone cells. Androgen deprivation therapy does not raise parathyroid hormone through renal calcium mechanisms, and the anemia-osteoblast pathway is not the primary mechanism.

Question 14

A patient receives goserelin acetate implant for prostate cancer. The nurse administering the injection inadvertently places the implant intramuscularly rather than subcutaneously. Which of the following best describes the pharmacological consequence of incorrect placement?

A)Intramuscular placement accelerates absorption of goserelin, producing a larger initial testosterone flare than would occur with subcutaneous placement
B)Intramuscular placement has no effect on drug release because the poly(lactic-co-glycolic acid) microsphere matrix controls release independently of tissue type
C)Intramuscular placement within vascular muscle tissue prevents the controlled slow release mechanism of the biodegradable implant, potentially resulting in erratic drug delivery and failure to maintain castrate testosterone levels
D)Intramuscular placement increases local inflammatory response, inactivating goserelin peptide bonds before systemic absorption can occur

Correct Answer

C) Intramuscular placement within vascular muscle tissue prevents the controlled slow release mechanism of the biodegradable implant, potentially resulting in erratic drug delivery and failure to maintain castrate testosterone levels

Rationale

The goserelin acetate implant (Zoladex) is a solid biodegradable rod designed for subcutaneous placement, where the controlled hydrolysis of the polymer matrix slowly releases drug over 28 or 84 days. Intramuscular placement disrupts this controlled release mechanism: the vascular and mechanical environment of muscle tissue is not designed for depot polymer hydrolysis, and drug may be released erratically or at an accelerated rate, preventing the sustained castrate testosterone levels the implant is designed to maintain. This is a clinically important administration requirement unique to goserelin among the commonly used gonadotropin-releasing hormone agonist formulations; other depot formulations such as leuprolide microsphere and triptorelin are given intramuscularly.

Clinical Correlations · Questions 15–18

Apply pharmacological knowledge to clinical scenarios. Each vignette presents a patient situation; the question tests mechanism of action or drug selection.

Question 15

A 32-year-old woman with endometriosis has been taking leuprolide depot 3.75 milligrams monthly for 7 months for pelvic pain. She now reports new low back pain. Dual-energy X-ray absorptiometry shows a lumbar spine bone mineral density 5.2% below her baseline measured before starting therapy. Which of the following best explains the mechanism of her bone loss?

A)Leuprolide directly activates osteoclast gonadotropin-releasing hormone receptors, stimulating bone resorption independent of estrogen suppression
B)Leuprolide-induced suppression of estradiol removes the inhibitory effect of estrogen on osteoclast activity, increasing bone resorption and reducing bone formation at trabecular surfaces
C)Leuprolide raises follicle-stimulating hormone levels above baseline, and elevated follicle-stimulating hormone directly stimulates osteoclast differentiation through a receptor-mediated pathway
D)Leuprolide suppresses progesterone synthesis, and progesterone deficiency rather than estrogen deficiency is the primary driver of bone loss during gonadotropin-releasing hormone agonist therapy

Correct Answer

B) Leuprolide-induced suppression of estradiol removes the inhibitory effect of estrogen on osteoclast activity, increasing bone resorption and reducing bone formation at trabecular surfaces

Rationale

Leuprolide depot produces profound estradiol suppression through gonadotropin-releasing hormone receptor downregulation. Estrogen normally suppresses RANK ligand expression on osteoblasts and promotes osteoclast apoptosis, thereby restraining bone resorption. Removal of this estrogenic protection shifts the bone remodeling balance toward net resorption. Bone mineral density loss of approximately 4 to 6% at the lumbar spine occurs over 6 months of depot gonadotropin-releasing hormone agonist therapy in premenopausal women. Add-back therapy with low-dose estrogen and progestin attenuates this loss. Leuprolide does not directly activate osteoclast receptors, and follicle-stimulating hormone is suppressed, not elevated, during gonadotropin-releasing hormone agonist therapy.

Question 16

A 67-year-old man with metastatic prostate cancer and known T8 vertebral metastasis is scheduled to begin leuprolide depot therapy. His oncologist explains that a co-medication is required for the first 4 weeks to prevent a serious complication related to therapy initiation. Which of the following drugs is most appropriate, and what is its mechanism of action in this setting?

A)Degarelix; competitively blocks the gonadotropin-releasing hormone receptor without initial activation, preventing the testosterone flare
B)Octreotide; suppresses luteinizing hormone secretion from the pituitary through somatostatin receptor-mediated Gi signaling
C)Bromocriptine; activates dopamine type 2 receptors on pituitary gonadotroph cells, suppressing luteinizing hormone release during the flare period
D)Bicalutamide; blocks androgen receptors in target tissues including bone, preventing testosterone from exerting stimulatory effects on metastases during the initial flare period

Correct Answer

D) Bicalutamide; blocks androgen receptors in target tissues including bone, preventing testosterone from exerting stimulatory effects on metastases during the initial flare period

Rationale

The testosterone flare associated with leuprolide depot initiation poses risk of spinal cord compression in patients with vertebral metastases. The standard management is bicalutamide, a non-steroidal anti-androgen that competitively blocks androgen receptors in target tissues. By occupying androgen receptors at metastatic sites in bone, bicalutamide prevents the transiently elevated testosterone produced during the first 1 to 2 weeks from driving tumor growth and worsening cord compression. It is begun 7 to 14 days before the first depot injection and continued for 4 weeks. Degarelix would be an alternative to leuprolide (avoiding the flare entirely) but is not a co-medication added to leuprolide. Octreotide and bromocriptine have no role in flare prevention.

Question 17

A 70-year-old man with prostate cancer has been taking relugolix 120 milligrams daily with stable castrate testosterone levels for 6 months. He is admitted for atrial fibrillation and started on amiodarone. At his next oncology visit 3 weeks later, his testosterone is undetectable and he reports worsening fatigue, hot flashes, and new-onset muscle weakness more pronounced than before amiodarone was added. Which of the following best explains this clinical change?

A)Amiodarone inhibits P-glycoprotein, reducing intestinal efflux of relugolix and increasing its plasma concentration, deepening androgen deprivation and intensifying hypogonadic adverse effects
B)Amiodarone induces cytochrome P450 3A4, accelerating relugolix metabolism and paradoxically producing an initial spike in active metabolite concentration before clearance increases
C)Amiodarone competes with relugolix for gonadotropin-releasing hormone receptor binding, producing additive receptor blockade and more complete testosterone suppression
D)Amiodarone inhibits renal tubular secretion of relugolix, reducing urinary clearance and raising steady-state plasma concentrations

Correct Answer

A) Amiodarone inhibits P-glycoprotein, reducing intestinal efflux of relugolix and increasing its plasma concentration, deepening androgen deprivation and intensifying hypogonadic adverse effects

Rationale

Relugolix is a P-glycoprotein substrate. Amiodarone is a potent P-glycoprotein inhibitor. Inhibition of intestinal P-glycoprotein reduces efflux of relugolix back into the gut lumen, increasing net absorption and raising plasma relugolix concentrations substantially. Higher relugolix levels produce deeper gonadotropin-releasing hormone receptor blockade and more complete testosterone suppression, intensifying hypogonadic symptoms including hot flashes, fatigue, and loss of muscle mass. This combination is contraindicated or requires dose adjustment. Amiodarone does not induce cytochrome P450 3A4 (it inhibits cytochrome P450 enzymes). Amiodarone has no activity at the gonadotropin-releasing hormone receptor. Relugolix is not eliminated primarily by renal tubular secretion.

Question 18

A 26-year-old woman with Kallmann syndrome and hypogonadotropic hypogonadism wishes to conceive. She has undetectable luteinizing hormone and follicle-stimulating hormone with a structurally normal pituitary on magnetic resonance imaging. Her physician considers either exogenous gonadotropins or pulsatile gonadotropin-releasing hormone pump therapy. Which of the following best explains why pulsatile gonadotropin-releasing hormone pump therapy is selected based on its mechanism of action?

A)Pulsatile gonadotropin-releasing hormone produces continuous receptor occupancy, which causes gonadotropin-releasing hormone receptor upregulation and an amplified follicle-stimulating hormone response sufficient to support follicular development
B)Pulsatile gonadotropin-releasing hormone directly stimulates ovarian follicular granulosa cells through a receptor-mediated pathway that bypasses the pituitary entirely
C)Pulsatile gonadotropin-releasing hormone delivered at physiological intervals maintains gonadotropin-releasing hormone receptor sensitivity, restoring pulsatile luteinizing hormone and follicle-stimulating hormone secretion from the intact pituitary and supporting natural follicular development
D)Pulsatile gonadotropin-releasing hormone suppresses hypothalamic dopamine release, removing inhibitory dopaminergic tone on pituitary gonadotrophs and allowing autonomous gonadotropin secretion to resume

Correct Answer

C) Pulsatile gonadotropin-releasing hormone delivered at physiological intervals maintains gonadotropin-releasing hormone receptor sensitivity, restoring pulsatile luteinizing hormone and follicle-stimulating hormone secretion from the intact pituitary and supporting natural follicular development

Rationale

In Kallmann syndrome, the defect is absent pulsatile gonadotropin-releasing hormone secretion from the hypothalamus; the pituitary gonadotrophs are intact and fully capable of responding to gonadotropin-releasing hormone. A portable pump delivers gonadotropin-releasing hormone in pulses every 60 to 120 minutes, mimicking physiological hypothalamic secretion. This pattern maintains gonadotropin-releasing hormone receptor sensitivity rather than causing downregulation, restoring pulsatile luteinizing hormone and follicle-stimulating hormone release and supporting follicular development. Cumulative pregnancy rates of 80 to 90% are achievable over multiple cycles. Continuous infusion would cause receptor downregulation and suppress gonadotropins. Gonadotropin-releasing hormone does not act directly on ovarian cells and does not suppress dopamine as its primary mechanism here.