Introduction to Medical Pharmacology

Hypothalamic Hormones and Receptor Pharmacology

Module 4 — Pituitary Adenoma Pharmacotherapy

Question 0 of 18

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 best describes the pharmacokinetic property that allows cabergoline to be administered twice weekly rather than daily or multiple times daily?

  • A)A plasma half-life of approximately 6 to 8 hours requiring twice or three times daily dosing
  • B)A plasma elimination half-life of approximately 63 to 68 hours enabling twice-weekly oral dosing
  • C)An oral bioavailability exceeding 95% that allows a smaller dose given once monthly to achieve sustained therapeutic concentrations
  • D)Extensive tissue redistribution producing a prolonged apparent half-life despite rapid plasma clearance

Correct Answer

B) A plasma elimination half-life of approximately 63 to 68 hours enabling twice-weekly oral dosing

Rationale

Cabergoline has an elimination half-life of approximately 63 to 68 hours, enabling twice-weekly oral dosing. This distinguishes it pharmacokinetically from bromocriptine, which has a half-life of approximately 6 to 8 hours and requires twice or three times daily dosing. The long half-life of cabergoline reflects extensive tissue binding and its ergot structure rather than depot formulation or exceptional bioavailability.

Question 2

Which of the following correctly classifies mifepristone according to its pharmacological mechanism in the treatment of Cushing syndrome?

  • A)Cytochrome P450 11B1 inhibitor that blocks the final step of cortisol biosynthesis
  • B)Pan-somatostatin receptor agonist that suppresses adrenocorticotropic hormone secretion from corticotroph adenoma cells
  • C)Adrenolytic agent that destroys adrenocortical cells and inhibits multiple steroidogenic enzymes
  • D)Glucocorticoid receptor antagonist that blocks cortisol action at target tissues without reducing cortisol production

Correct Answer

D) Glucocorticoid receptor antagonist that blocks cortisol action at target tissues without reducing cortisol production

Rationale

Mifepristone is a glucocorticoid receptor antagonist. It binds the glucocorticoid receptor with approximately threefold higher affinity than cortisol and prevents glucocorticoid signaling at target tissues. Unlike steroidogenesis inhibitors, mifepristone does not reduce cortisol production; serum cortisol and adrenocorticotropic hormone actually rise during therapy because glucocorticoid receptor blockade eliminates hypothalamic-pituitary negative feedback. Cytochrome P450 11B1 inhibition describes metyrapone and osilodrostat. Pan-somatostatin receptor agonism describes pasireotide. Adrenolytic activity describes mitotane.

Question 3

Which of the following correctly identifies the primary enzyme target of metyrapone?

  • A)Cytochrome P450 11B1 (11-beta-hydroxylase), the enzyme catalyzing the final step of cortisol synthesis
  • B)Cytochrome P450 11A1 (cholesterol side-chain cleavage enzyme), the rate-limiting first step of steroidogenesis
  • C)Cytochrome P450 17A1 (17-alpha-hydroxylase/17,20-lyase), the enzyme required for both cortisol and androgen synthesis
  • D)Cytochrome P450 11B2 (aldosterone synthase), the terminal enzyme of aldosterone biosynthesis

Correct Answer

A) Cytochrome P450 11B1 (11-beta-hydroxylase), the enzyme catalyzing the final step of cortisol synthesis

Rationale

Metyrapone selectively inhibits cytochrome P450 11B1, the enzyme that catalyzes 11-beta-hydroxylation of 11-deoxycortisol to cortisol — the final step in cortisol biosynthesis. This block causes 11-deoxycortisol to accumulate proximal to the block and is measurable as a surrogate marker of drug action. Because the block is proximal to cytochrome P450 11B2 (aldosterone synthase), mineralocorticoid precursors including 11-deoxycorticosterone also accumulate, causing sodium retention, hypertension, and hypokalemia. Ketoconazole inhibits cytochrome P450 11A1 and P450 17A1 in addition to other steps. Aldosterone synthase (cytochrome P450 11B2) inhibition is an additional property of osilodrostat, not metyrapone.

Question 4

Which of the following correctly classifies mitotane according to its pharmacological mechanism and drug interaction profile?

  • A)Selective cytochrome P450 11B1 inhibitor with moderate cytochrome P450 2D6 inhibition
  • B)Glucocorticoid receptor antagonist with potent cytochrome P450 3A4 inhibition
  • C)Adrenolytic agent that destroys adrenocortical cells and is a potent inducer of cytochrome P450 3A4 and cytochrome P450 2B6
  • D)Pan-somatostatin receptor agonist with cytochrome P450 3A4 substrate pharmacokinetics

Correct Answer

C) Adrenolytic agent that destroys adrenocortical cells and is a potent inducer of cytochrome P450 3A4 and cytochrome P450 2B6

Rationale

Mitotane is an adrenolytic agent derived from the insecticide DDT that produces selective destruction of the adrenal cortex through formation of reactive acyl chloride intermediates that alkylate adrenocortical cell proteins. In addition to its cytotoxic and steroidogenesis-inhibiting effects, mitotane is a potent inducer of cytochrome P450 3A4 and cytochrome P450 2B6. This induction substantially accelerates the metabolism of warfarin, glucocorticoids, and oral contraceptives — requiring substantial dose increases or alternative contraception. Selective cytochrome P450 11B1 inhibition describes metyrapone. Glucocorticoid receptor antagonism with cytochrome P450 3A4 inhibition describes mifepristone. Pan-somatostatin receptor agonism describes pasireotide.

Question 5

Which of the following best distinguishes osilodrostat from metyrapone in terms of enzyme inhibition profile?

  • A)Osilodrostat selectively inhibits cytochrome P450 11B1, while metyrapone inhibits both cytochrome P450 11B1 and cytochrome P450 11B2
  • B)Osilodrostat inhibits both cytochrome P450 11B1 (11-beta-hydroxylase) and cytochrome P450 11B2 (aldosterone synthase), while metyrapone selectively inhibits cytochrome P450 11B1 only
  • C)Osilodrostat is a prodrug that requires cytochrome P450 3A4 activation to inhibit 11-beta-hydroxylase, while metyrapone is active without metabolic conversion
  • D)Osilodrostat inhibits cytochrome P450 17A1 in addition to cytochrome P450 11B1, while metyrapone is confined to cytochrome P450 11B1

Correct Answer

B) Osilodrostat inhibits both cytochrome P450 11B1 (11-beta-hydroxylase) and cytochrome P450 11B2 (aldosterone synthase), while metyrapone selectively inhibits cytochrome P450 11B1 only

Rationale

Osilodrostat inhibits both cytochrome P450 11B1 (11-beta-hydroxylase, the final step in cortisol synthesis) and cytochrome P450 11B2 (aldosterone synthase). The additional aldosterone synthase inhibition distinguishes it from metyrapone, which selectively inhibits cytochrome P450 11B1. Because osilodrostat suppresses aldosterone synthesis, it can cause aldosterone deficiency manifesting as hypotension, hypokalemia, and electrolyte disturbances — in contrast to metyrapone, where mineralocorticoid precursor accumulation proximal to the aldosterone synthase step causes the opposite mineralocorticoid excess effect. Both agents require cortisol monitoring and carry adrenal insufficiency risk at full cortisol suppression.

Question 6

Which of the following correctly classifies ketoconazole according to its dual pharmacological role in Cushing syndrome management?

  • A)A steroidogenesis inhibitor that blocks multiple adrenal cytochrome P450 enzymes and is itself a potent inhibitor of cytochrome P450 3A4, producing numerous drug interactions
  • B)A selective cytochrome P450 11B1 inhibitor that is a potent inducer of cytochrome P450 3A4, accelerating metabolism of co-administered drugs
  • C)A glucocorticoid receptor antagonist that also inhibits cytochrome P450 3A4, increasing exposure of cytochrome P450 3A4-metabolized glucocorticoids
  • D)An adrenolytic agent that destroys adrenocortical cells and inhibits cytochrome P450 3A4, requiring monitoring for drug-drug interactions

Correct Answer

A) A steroidogenesis inhibitor that blocks multiple adrenal cytochrome P450 enzymes and is itself a potent inhibitor of cytochrome P450 3A4, producing numerous drug interactions

Rationale

Ketoconazole is an imidazole antifungal repurposed as a steroidogenesis inhibitor. It blocks multiple adrenal cytochrome P450 enzymes — principally cytochrome P450 11A1, cytochrome P450 11B1, and cytochrome P450 17A1 — reducing cortisol synthesis across multiple steps. It is simultaneously a potent inhibitor of cytochrome P450 3A4, dramatically increasing plasma concentrations of many co-administered drugs including cyclosporine, tacrolimus, statins, calcium channel blockers, and midazolam. This places it in a different drug interaction category from mitotane, which is a cytochrome P450 3A4 inducer rather than inhibitor. Selective cytochrome P450 11B1 inhibition with cytochrome P450 3A4 induction describes neither ketoconazole nor any approved agent in this class.

Core Pharmacology  ·  Questions 7–14

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

Question 7

Long-term cabergoline therapy is associated with cardiac valve fibrosis, particularly at the tricuspid and mitral valves. Which of the following best explains the mechanism of this adverse effect?

  • A)Cabergoline activates dopamine type 2 receptors on cardiac valve fibroblasts, stimulating collagen synthesis and progressive valve thickening through a Gi-mediated pathway
  • B)Cabergoline reduces portal dopamine delivery by suppressing hypothalamic tuberoinfundibular neurons, producing systemic dopamine deficiency that impairs cardiac valve homeostasis
  • C)Cabergoline activates serotonin 5-hydroxytryptamine 2B receptors on cardiac valve fibroblasts, stimulating fibroblast proliferation and collagen deposition — a mechanism unrelated to its therapeutic dopamine type 2 receptor agonism
  • D)Cabergoline inhibits cardiac voltage-gated potassium channels at therapeutic doses, producing fibrotic remodeling of valve leaflets through calcium overload in valve interstitial cells

Correct Answer

C) Cabergoline activates serotonin 5-hydroxytryptamine 2B receptors on cardiac valve fibroblasts, stimulating fibroblast proliferation and collagen deposition — a mechanism unrelated to its therapeutic dopamine type 2 receptor agonism

Rationale

Cardiac valvulopathy from cabergoline is mediated by agonist activity at serotonin 5-hydroxytryptamine 2B receptors on cardiac valve fibroblasts. Activation of these receptors stimulates fibroblast proliferation and collagen deposition, producing the characteristic fibrotic thickening of valve leaflets seen with ergot derivatives. This mechanism is entirely distinct from and independent of the therapeutic dopamine type 2 receptor agonism responsible for prolactin suppression and tumor shrinkage. The same 5-hydroxytryptamine 2B receptor mechanism explains valvulopathy from fenfluramine and ergotamine. At the low cumulative doses used for prolactinoma, the risk appears to be substantially lower than at the high doses used in Parkinson disease treatment.

Question 8

A patient with Cushing syndrome is started on mifepristone. At a follow-up visit, her serum cortisol is 72 mcg/dL (reference range 5 to 25 mcg/dL in the morning) and her adrenocorticotropic hormone is markedly elevated. Her blood glucose has normalized and her cushingoid features are improving. Which of the following best explains why the elevated serum cortisol should not be interpreted as treatment failure?

  • A)Mifepristone blocks the glucocorticoid receptor at hypothalamic and pituitary neurons, eliminating the cortisol-mediated negative feedback signal; the pituitary responds by increasing adrenocorticotropic hormone secretion, which drives adrenal cortisol output upward — a predictable pharmacodynamic consequence of effective receptor blockade that does not indicate inadequate treatment
  • B)Mifepristone undergoes enterohepatic recirculation that transiently suppresses cortisol binding to plasma proteins, producing artifactually elevated free cortisol measurements on standard assays
  • C)The elevated cortisol reflects rebound hypercortisolism from transient adrenal hypertrophy that occurs in the first months of mifepristone therapy before the adrenal cortex adapts to glucocorticoid receptor blockade
  • D)Standard cortisol immunoassays cross-react with mifepristone and its metabolites, producing falsely elevated cortisol readings that normalize when a mass spectrometry-based cortisol assay is used

Correct Answer

A) Mifepristone blocks the glucocorticoid receptor at hypothalamic and pituitary neurons, eliminating the cortisol-mediated negative feedback signal; the pituitary responds by increasing adrenocorticotropic hormone secretion, which drives adrenal cortisol output upward — a predictable pharmacodynamic consequence of effective receptor blockade that does not indicate inadequate treatment

Rationale

Mifepristone blocks glucocorticoid receptors throughout the body, including in hypothalamic and pituitary cells that mediate cortisol negative feedback. Without functional glucocorticoid receptor signaling, the hypothalamus and pituitary do not register cortisol excess and drive adrenocorticotropic hormone secretion upward. The resulting adrenocorticotropic hormone excess stimulates the adrenal cortex to produce more cortisol. This is the expected and mechanistically inevitable pharmacodynamic response to effective glucocorticoid receptor blockade — it does not indicate treatment failure. Treatment adequacy is assessed by clinical endpoints: blood glucose control, blood pressure, weight, and regression of cushingoid features. Cortisol and urinary free cortisol levels are non-informative and must not be used to monitor mifepristone therapy.

Question 9

A patient with Cushing disease is started on metyrapone for cortisol control while awaiting repeat surgery. After 3 weeks, she develops hypertension and hypokalemia. Which of the following best explains the mechanism of these findings?

  • A)Metyrapone inhibits cytochrome P450 11B2 (aldosterone synthase), eliminating aldosterone production and causing a mineralocorticoid excess state through a compensatory increase in other sodium-retaining steroids
  • B)Metyrapone directly activates mineralocorticoid receptors in the renal tubule, producing aldosterone-like effects that cause sodium retention, potassium wasting, and hypertension
  • C)Metyrapone inhibits cytochrome P450 17A1, causing androgen precursors to be redirected into the mineralocorticoid pathway, increasing 11-deoxycorticosterone synthesis
  • D)Metyrapone inhibits cytochrome P450 11B1, blocking the conversion of 11-deoxycortisol to cortisol; proximal to this block, 11-deoxycorticosterone — a mineralocorticoid precursor with sodium-retaining activity — accumulates and activates mineralocorticoid receptors, causing hypertension and hypokalemia

Correct Answer

D) Metyrapone inhibits cytochrome P450 11B1, blocking the conversion of 11-deoxycortisol to cortisol; proximal to this block, 11-deoxycorticosterone — a mineralocorticoid precursor with sodium-retaining activity — accumulates and activates mineralocorticoid receptors, causing hypertension and hypokalemia

Rationale

Metyrapone selectively inhibits cytochrome P450 11B1, which is responsible for 11-beta-hydroxylation of both 11-deoxycortisol to cortisol and 11-deoxycorticosterone to corticosterone. When cytochrome P450 11B1 is blocked, 11-deoxycorticosterone accumulates proximal to the block. Unlike cortisol, 11-deoxycorticosterone has significant mineralocorticoid activity and activates renal mineralocorticoid receptors, promoting sodium retention, potassium excretion, and hypertension. This effect is compounded by the fact that blocked cortisol synthesis drives adrenocorticotropic hormone to rise, stimulating greater mineralocorticoid precursor production. Metyrapone does not inhibit cytochrome P450 11B2 (aldosterone synthase), does not directly activate mineralocorticoid receptors, and does not redirect androgen precursors into the mineralocorticoid pathway.

Question 10

A patient with adrenocortical carcinoma begins mitotane therapy. He has been taking warfarin for atrial fibrillation with a stable international normalized ratio of 2.4 for the past year. Four weeks after starting mitotane, his international normalized ratio has fallen to 1.2 despite no change in his warfarin dose. Which of the following best explains this drug interaction?

  • A)Mitotane displaces warfarin from plasma protein binding sites, transiently increasing free warfarin concentration and paradoxically increasing warfarin clearance through saturation of hepatic elimination pathways
  • B)Mitotane is a potent inducer of cytochrome P450 3A4 and cytochrome P450 2B6, enzymes that participate in warfarin metabolism; increased enzyme activity substantially accelerates warfarin clearance, reducing anticoagulant effect and requiring warfarin dose increases of 50% or more
  • C)Mitotane inhibits cytochrome P450 2C9, the primary enzyme responsible for warfarin metabolism, which paradoxically increases warfarin clearance through shunting to alternative metabolic pathways
  • D)Mitotane reduces hepatic synthesis of clotting factors through adrenolytic mechanisms that impair hepatic mitochondrial function, requiring warfarin dose reduction to prevent bleeding

Correct Answer

B) Mitotane is a potent inducer of cytochrome P450 3A4 and cytochrome P450 2B6, enzymes that participate in warfarin metabolism; increased enzyme activity substantially accelerates warfarin clearance, reducing anticoagulant effect and requiring warfarin dose increases of 50% or more

Rationale

Mitotane is a potent inducer of cytochrome P450 3A4 and cytochrome P450 2B6. Induction of these enzymes substantially increases the rate of warfarin metabolism (warfarin is a substrate of multiple cytochrome P450 enzymes including cytochrome P450 2C9, 3A4, and 1A2), reducing warfarin plasma concentrations and anticoagulant effect. The fall in international normalized ratio reflects reduced warfarin exposure from accelerated clearance, not reduced clotting factor synthesis or protein binding displacement. Warfarin dose increases of 50% or more are typically required when mitotane is co-administered. Mitotane does not inhibit cytochrome P450 2C9, and its adrenolytic mechanism does not directly impair hepatic clotting factor synthesis.

Question 11

A woman with prolactinoma and schizophrenia is taking cabergoline for hyperprolactinemia. Her psychiatrist adds haloperidol for psychosis management. Despite continued cabergoline, her serum prolactin rises significantly. Which of the following best explains this pharmacodynamic interaction?

  • A)Haloperidol induces cytochrome P450 3A4, substantially increasing cabergoline first-pass metabolism and reducing plasma cabergoline concentrations below the therapeutic threshold
  • B)Haloperidol activates serotonin 5-hydroxytryptamine 2B receptors on lactotroph cells, stimulating prolactin gene transcription through a pathway independent of dopamine receptor signaling
  • C)Haloperidol competitively blocks dopamine type 2 receptors on pituitary lactotroph cells, preventing cabergoline from exerting its tonic inhibitory effect on prolactin secretion
  • D)Haloperidol reduces hypothalamic tuberoinfundibular dopaminergic neuron firing through a presynaptic mechanism, decreasing portal dopamine delivery and partially overcoming the therapeutic effect of cabergoline at the pituitary level

Correct Answer

C) Haloperidol competitively blocks dopamine type 2 receptors on pituitary lactotroph cells, preventing cabergoline from exerting its tonic inhibitory effect on prolactin secretion

Rationale

Cabergoline works by activating dopamine type 2 receptors on pituitary lactotroph cells, mimicking the tonic inhibitory dopamine signal that normally suppresses prolactin secretion. Haloperidol is a potent dopamine type 2 receptor antagonist. At the pituitary, haloperidol competes with cabergoline for the same receptor, blocking access to dopamine type 2 receptors and preventing the agonist from exerting its prolactin-suppressing effect. The result is a pharmacodynamic antagonism that can substantially blunt or abolish cabergoline efficacy. This interaction is a class effect of all dopamine type 2 receptor antagonists, including other antipsychotics and metoclopramide. Haloperidol does not induce cytochrome P450 3A4, does not activate serotonin receptors on lactotrophs as a primary mechanism, and the presynaptic tuberoinfundibular pathway is not the primary interaction site.

Question 12

Pasireotide is approved for Cushing disease, where corticotroph adenoma cells express somatostatin receptor subtype 5 more abundantly than somatostatin receptor subtype 2. Which of the following best explains the mechanism by which pasireotide suppresses adrenocorticotropic hormone secretion in this setting?

  • A)Pasireotide activates somatostatin receptor subtype 5 on corticotroph adenoma cells, coupling through Gi proteins to inhibit adenylyl cyclase and reduce cyclic adenosine monophosphate, suppressing pro-opiomelanocortin gene transcription and adrenocorticotropic hormone exocytosis
  • B)Pasireotide activates dopamine type 2 receptors on corticotroph adenoma cells, providing an inhibitory dopaminergic signal that reduces adrenocorticotropic hormone secretion through the same mechanism exploited by cabergoline
  • C)Pasireotide blocks corticotropin-releasing hormone receptor type 1 on corticotroph cells, preventing corticotropin-releasing hormone from activating Gs-coupled adenylyl cyclase and driving adrenocorticotropic hormone synthesis
  • D)Pasireotide activates glucocorticoid receptors on corticotroph cells, mimicking cortisol negative feedback and suppressing pro-opiomelanocortin gene transcription

Correct Answer

A) Pasireotide activates somatostatin receptor subtype 5 on corticotroph adenoma cells, coupling through Gi proteins to inhibit adenylyl cyclase and reduce cyclic adenosine monophosphate, suppressing pro-opiomelanocortin gene transcription and adrenocorticotropic hormone exocytosis

Rationale

Corticotroph adenoma cells express somatostatin receptor subtype 5 at higher density than somatostatin receptor subtype 2 — the reverse of the pattern in somatotroph adenomas. Pasireotide, as a pan-somatostatin receptor agonist with particularly high somatostatin receptor subtype 5 affinity, activates these receptors on corticotroph cells. Somatostatin receptor subtype 5 couples through Gi proteins to inhibit adenylyl cyclase, lowering intracellular cyclic adenosine monophosphate and reducing protein kinase A activity. This suppresses pro-opiomelanocortin gene transcription and adrenocorticotropic hormone secretory vesicle exocytosis. Pasireotide does not activate dopamine type 2 receptors (that is the mechanism of cabergoline), does not block corticotropin-releasing hormone receptor type 1, and does not activate glucocorticoid receptors.

Question 13

A patient with Cushing disease is started on ketoconazole for cortisol lowering while awaiting repeat pituitary surgery. Which of the following monitoring requirements is most critical during the initiation phase of ketoconazole therapy?

  • A)Serum potassium and blood pressure monitoring every 2 weeks to detect mineralocorticoid precursor accumulation from 11-deoxycorticosterone buildup
  • B)Corrected QT interval measurement by electrocardiogram weekly during the first month, as ketoconazole-associated QT prolongation typically manifests within the first 4 to 6 weeks
  • C)Serum adrenocorticotropic hormone measurement every 2 to 4 weeks to confirm that ketoconazole is suppressing adrenocorticotropic hormone secretion from the corticotroph adenoma
  • D)Liver function tests every 2 to 4 weeks during initiation and monthly thereafter, because ketoconazole causes elevated liver enzymes in up to 20% of patients and severe hepatotoxicity in up to 3%

Correct Answer

D) Liver function tests every 2 to 4 weeks during initiation and monthly thereafter, because ketoconazole causes elevated liver enzymes in up to 20% of patients and severe hepatotoxicity in up to 3%

Rationale

Ketoconazole carries significant hepatotoxicity risk: elevated liver enzymes occur in up to 20% of patients and severe hepatotoxicity requiring drug discontinuation occurs in up to 3%. Liver function test monitoring every 2 to 4 weeks during initiation and monthly thereafter is a mandatory surveillance requirement. While ketoconazole also prolongs the corrected QT interval through hERG potassium channel inhibition, electrocardiographic monitoring is not required at the weekly frequency described in option B — baseline electrocardiogram and awareness of the risk are the standard recommendations. Serum potassium monitoring for mineralocorticoid precursor accumulation applies to metyrapone, not ketoconazole (which inhibits multiple enzymes including cytochrome P450 11A1, reducing total steroidogenesis rather than causing selective proximal precursor accumulation). Ketoconazole does not suppress adrenocorticotropic hormone at the pituitary level.

Question 14

A patient with refractory Cushing disease undergoes bilateral adrenalectomy. Eighteen months later, she develops hyperpigmentation, progressive bitemporal hemianopia, and a serum adrenocorticotropic hormone of 840 pg/mL. Which of the following best explains the pathophysiology of her new presentation?

  • A)Bilateral adrenalectomy removes aldosterone as well as cortisol; the resulting mineralocorticoid deficiency drives compensatory adrenocorticotropic hormone hypersecretion that stimulates adrenocorticotropic hormone-responsive melanocytes in the skin
  • B)Removing the adrenal glands eliminates cortisol production and abolishes cortisol-mediated negative feedback on the hypothalamus and pituitary; the residual corticotroph adenoma — no longer restrained by cortisol feedback — expands aggressively, producing extreme adrenocorticotropic hormone hypersecretion and tumor mass effects on the optic chiasm
  • C)Bilateral adrenalectomy triggers an autoimmune response against pituitary corticotroph cells, stimulating inflammatory growth factors that drive adenoma expansion independent of the hypothalamic-pituitary-adrenal feedback axis
  • D)The adrenal glands produce an unidentified inhibitory factor that normally restrains pituitary corticotroph adenoma growth; removal of this factor allows the tumor to escape growth suppression

Correct Answer

B) Removing the adrenal glands eliminates cortisol production and abolishes cortisol-mediated negative feedback on the hypothalamus and pituitary; the residual corticotroph adenoma — no longer restrained by cortisol feedback — expands aggressively, producing extreme adrenocorticotropic hormone hypersecretion and tumor mass effects on the optic chiasm

Rationale

Nelson syndrome occurs when bilateral adrenalectomy for refractory Cushing disease removes the source of cortisol, permanently eliminating the negative feedback that cortisol normally exerts on the hypothalamus and pituitary. The residual corticotroph adenoma, previously partially restrained by cortisol feedback, now receives unopposed stimulation from hypothalamic corticotropin-releasing hormone with no cortisol to suppress the axis. The adenoma can enlarge rapidly, producing visual field loss from optic chiasm compression and extremely high adrenocorticotropic hormone levels. The markedly elevated adrenocorticotropic hormone drives melanocyte-stimulating hormone activity (pro-opiomelanocortin cleavage product), producing the characteristic hyperpigmentation. The mechanism is pure loss of negative feedback, not autoimmune, not mineralocorticoid-mediated, and not related to any adrenal inhibitory factor.

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 28-year-old woman with a microadenoma-associated prolactinoma has been taking cabergoline 0.5 mg twice weekly for 18 months with prolactin normalization and no visible tumor on magnetic resonance imaging. She now wishes to conceive. Her endocrinologist discusses switching her medication before attempting pregnancy. Which of the following drugs is most appropriate, and what is the primary rationale for the switch?

  • A)Pasireotide; its longer half-life and pan-somatostatin receptor activity suppress prolactin more reliably during the first trimester when tumor growth risk is highest
  • B)Leuprolide depot; suppressing luteinizing hormone and follicle-stimulating hormone during the first trimester prevents the estrogen surge that can drive prolactinoma expansion
  • C)Metyrapone; reducing cortisol during early pregnancy lowers the risk of gestational Cushing syndrome, which exacerbates prolactinoma growth in predisposed patients
  • D)Bromocriptine; it has the longest safety record in pregnancy — over four decades of reassuring first-trimester exposure data — making it the preferred dopamine agonist when conception is planned or confirmed

Correct Answer

D) Bromocriptine; it has the longest safety record in pregnancy — over four decades of reassuring first-trimester exposure data — making it the preferred dopamine agonist when conception is planned or confirmed

Rationale

Bromocriptine is the preferred dopamine agonist during pregnancy because of its unmatched safety record: over four decades of data in thousands of pregnancies have not revealed significant teratogenic risk with first-trimester exposure. Cabergoline has less extensive pregnancy safety data, and many centers switch patients planning pregnancy from cabergoline to bromocriptine before conception, or discontinue dopamine agonists entirely once pregnancy is confirmed in patients with microadenomas. In microadenomas, tumor enlargement during pregnancy is uncommon (less than 5%), and most patients can discontinue dopamine agonist therapy safely after conception. Pasireotide, leuprolide, and metyrapone have no role in prolactinoma management during pregnancy and would be inappropriate in this setting.

Question 16

A 45-year-old woman with Cushing syndrome from an adrenocortical adenoma is treated with mifepristone after failing surgical resection. At a routine visit 3 months into therapy, she reports progressive fatigue, nausea, and lightheadedness over the past week. Her blood pressure is 84/52 mmHg and serum cortisol is 68 mcg/dL. Which of the following best explains why the markedly elevated serum cortisol does not exclude a diagnosis of adrenal insufficiency in this patient?

  • A)Mifepristone blocks the glucocorticoid receptor, preventing cortisol from exerting negative feedback on the hypothalamus and pituitary; adrenocorticotropic hormone rises and drives high cortisol production, but cortisol cannot act at its receptor in target tissues — including the brain and vasculature — producing the clinical syndrome of functional glucocorticoid deficiency despite supranormal serum cortisol
  • B)Mifepristone undergoes enterohepatic recirculation that displaces cortisol from cortisol-binding globulin, increasing total cortisol measurement while free cortisol is paradoxically low, producing a discordance between total cortisol and biologically active cortisol
  • C)At toxic doses of mifepristone, the drug inhibits adrenal cytochrome P450 enzymes, paradoxically reducing cortisol biosynthesis while the immunoassay reads elevated because it cross-reacts with cortisol precursors
  • D)Mifepristone suppresses hepatic cortisol-binding globulin synthesis, reducing bound cortisol and increasing the urinary excretion of free cortisol, leading to paradoxically high serum total cortisol despite normal free cortisol at tissues

Correct Answer

A) Mifepristone blocks the glucocorticoid receptor, preventing cortisol from exerting negative feedback on the hypothalamus and pituitary; adrenocorticotropic hormone rises and drives high cortisol production, but cortisol cannot act at its receptor in target tissues — including the brain and vasculature — producing the clinical syndrome of functional glucocorticoid deficiency despite supranormal serum cortisol

Rationale

Mifepristone blocks glucocorticoid receptors throughout the body. With glucocorticoid receptors non-functional, the hypothalamus and pituitary lose cortisol negative feedback and drive adrenocorticotropic hormone and cortisol production to supraphysiological levels. However, at target tissues — including blood vessels, brain, and liver — cortisol cannot bind its receptor and cannot exert its physiological effects. The patient is therefore functionally glucocorticoid-deficient at the tissue level despite extreme cortisol production. Fatigue, nausea, and hypotension are clinical signs of glucocorticoid insufficiency that must be taken seriously. On mifepristone, serum cortisol cannot be used to diagnose adrenal insufficiency — clinical signs must guide the decision to provide stress-dose glucocorticoid coverage and to hold or discontinue mifepristone. The other options describe mechanisms that do not occur with mifepristone at clinical doses.

Question 17

A 52-year-old man with Cushing disease is started on ketoconazole 400 mg three times daily while awaiting repeat transsphenoidal surgery. After 3 weeks of therapy, his corrected QT interval on electrocardiogram is 498 milliseconds (baseline 412 milliseconds) and alanine aminotransferase is 4.2 times the upper limit of normal. Which of the following best explains both findings?

  • A)Ketoconazole inhibits hepatic mitochondrial function through its imidazole ring structure, causing hepatocyte energy failure that simultaneously impairs liver enzyme clearance and disrupts cardiac myocyte calcium handling, producing both liver enzyme elevations and corrected QT interval prolongation
  • B)Ketoconazole accumulates in cardiac and hepatic tissue because of its potent cytochrome P450 3A4 inhibition; elevated intracellular ketoconazole concentrations directly damage both cardiomyocytes and hepatocytes through oxidative stress
  • C)Ketoconazole prolongs the corrected QT interval by inhibiting cardiac hERG potassium channels (blocking IKr repolarizing current), and causes hepatotoxicity through a mechanism that produces elevation of liver enzymes in up to 20% of patients and severe hepatotoxicity in up to 3% — both are independent adverse effects of the drug requiring separate monitoring
  • D)Ketoconazole inhibits cytochrome P450 3A4 in the liver, reducing the metabolism of endogenous substrates that normally protect against hepatic oxidative injury, and simultaneously reducing metabolism of cardiac ion channel regulatory proteins, producing both effects through a single cytochrome P450 3A4-mediated pathway

Correct Answer

C) Ketoconazole prolongs the corrected QT interval by inhibiting cardiac hERG potassium channels (blocking IKr repolarizing current), and causes hepatotoxicity through a mechanism that produces elevation of liver enzymes in up to 20% of patients and severe hepatotoxicity in up to 3% — both are independent adverse effects of the drug requiring separate monitoring

Rationale

Ketoconazole causes corrected QT interval prolongation by inhibiting the hERG (human ether-a-go-go related gene) potassium channel, which conducts the rapid delayed rectifier potassium current (IKr) essential for ventricular repolarization. This is a direct channel-blocking effect. Separately and independently, ketoconazole causes hepatotoxicity through mechanisms that are not fully elucidated but produce clinically significant liver enzyme elevations in up to 20% of patients and severe hepatotoxicity in up to 3%. These are two distinct adverse effects that require independent monitoring: baseline electrocardiogram and awareness of QT risk for the cardiac effect, and liver function tests every 2 to 4 weeks during initiation for the hepatic effect. A corrected QT interval approaching 500 milliseconds and a fourfold alanine aminotransferase elevation both represent thresholds that should prompt dose reduction or discontinuation.

Question 18

A 38-year-old woman with Cushing disease underwent bilateral adrenalectomy 2 years ago after failing two transsphenoidal surgeries. She now presents with progressive skin darkening, right temporal visual field loss, and headaches. Magnetic resonance imaging shows a 2.4 cm pituitary mass with cavernous sinus invasion. Serum adrenocorticotropic hormone is 1,240 pg/mL. Which of the following best explains the mechanism responsible for her current presentation?

  • A)Autoimmune destruction of the remaining adrenocortical remnant triggered pituitary adrenocorticotropic hormone hypersecretion through a cross-reactive inflammatory response between adrenal and pituitary corticotroph antigens
  • B)Bilateral adrenalectomy permanently eliminated cortisol production, removing the negative feedback that cortisol exerts on the hypothalamus and pituitary; the residual corticotroph adenoma, no longer suppressed by cortisol, expanded aggressively under unopposed corticotropin-releasing hormone drive, producing extreme adrenocorticotropic hormone hypersecretion and tumor mass effects
  • C)Exogenous glucocorticoid replacement therapy administered after bilateral adrenalectomy paradoxically stimulated corticotroph adenoma growth through glucocorticoid receptor-mediated upregulation of pro-opiomelanocortin gene transcription
  • D)Loss of adrenal mineralocorticoid production after bilateral adrenalectomy elevated plasma renin activity, which stimulated pituitary corticotroph cell proliferation through angiotensin type 2 receptor-mediated growth signaling

Correct Answer

B) Bilateral adrenalectomy permanently eliminated cortisol production, removing the negative feedback that cortisol exerts on the hypothalamus and pituitary; the residual corticotroph adenoma, no longer suppressed by cortisol, expanded aggressively under unopposed corticotropin-releasing hormone drive, producing extreme adrenocorticotropic hormone hypersecretion and tumor mass effects

Rationale

This is Nelson syndrome: the development of an aggressive, rapidly enlarging corticotroph adenoma following bilateral adrenalectomy for refractory Cushing disease. When both adrenal glands are removed, cortisol production ceases permanently. Cortisol normally provides long-loop negative feedback to both the hypothalamus (suppressing corticotropin-releasing hormone) and the pituitary (suppressing adrenocorticotropic hormone secretion and corticotroph proliferation). Without this feedback, the residual corticotroph adenoma receives unopposed stimulation from hypothalamic corticotropin-releasing hormone and can expand rapidly, producing tumor mass effects on adjacent structures including the optic chiasm and cavernous sinuses. Markedly elevated adrenocorticotropic hormone drives pro-opiomelanocortin cleavage products including melanocyte-stimulating hormone, causing hyperpigmentation. The mechanism is pure loss of cortisol negative feedback — not autoimmune, not glucocorticoid replacement-mediated, and not renin-angiotensin related.