1. A 70-year-old man presents with newly diagnosed metastatic prostate cancer. Imaging shows extensive vertebral metastases with epidural tumor abutting the spinal cord at T10, and he reports new mild lower-extremity weakness. The oncology team plans to initiate androgen deprivation therapy urgently. The resident proposes starting monotherapy with a depot GnRH agonist (leuprolide) today. Which of the following is the most appropriate response regarding this plan?
A) Leuprolide monotherapy started today is ideal because GnRH agonists suppress testosterone immediately, eliminating any concern about tumor stimulation in this high-risk patient
B) Androgen deprivation should be deferred entirely until after the spinal cord compression resolves, because no form of hormonal therapy can be safely initiated in the presence of cord-threatening metastases
C) Leuprolide monotherapy risks a testosterone flare from transient GnRH receptor activation before downregulation, which could acutely worsen the epidural disease and neurologic deficit; the patient should instead receive a GnRH antagonist (e.g., degarelix), which suppresses testosterone immediately without a flare, or, if an agonist is used, it must be preceded by antiandrogen coverage
D) Leuprolide is contraindicated in prostate cancer altogether because GnRH agonists stimulate rather than suppress tumor growth over the long term
E) The patient should receive high-dose exogenous testosterone first to saturate tumor androgen receptors before starting leuprolide, preventing any subsequent flare response
ANSWER: C
Rationale:
This question asked you to apply GnRH agonist versus antagonist pharmacology to a prostate cancer patient at risk of spinal cord compression. A depot GnRH agonist such as leuprolide transiently activates the GnRH receptor before downregulation occurs, producing an initial surge of LH and testosterone (the flare) during the first one to two weeks. In a patient with epidural tumor abutting the cord and an evolving neurologic deficit, this testosterone flare could acutely stimulate tumor growth and precipitate or worsen cord compression. The correct management is to avoid unopposed agonist initiation: either start a GnRH antagonist (degarelix or relugolix), which competitively blocks the receptor and suppresses testosterone immediately without a flare, or, if an agonist is chosen, precede and overlap it with an antiandrogen (such as bicalutamide) to block the effect of the surging testosterone during the flare window.
Option A: Option A is incorrect because GnRH agonists do not suppress testosterone immediately — they cause an initial flare before suppression, which is precisely the danger in this patient.
Option B: Option B is incorrect because androgen deprivation should not be deferred entirely; it can and should be initiated safely using an antagonist or agonist-plus-antiandrogen strategy, and the cord compression itself requires prompt androgen deprivation along with steroids and consideration of radiation or surgery.
Option D: Option D is incorrect because GnRH agonists are a mainstay of prostate cancer therapy and suppress (not stimulate) tumor growth over the long term through sustained androgen deprivation; only the transient initial flare is problematic.
Option E: Option E is incorrect because giving exogenous testosterone would directly stimulate an androgen-sensitive tumor and worsen cord compression — it is dangerous and not a flare-prevention strategy.
2. A 48-year-old woman with acromegaly inadequately controlled on octreotide is switched to pasireotide, with subsequent good control of IGF-1. At her 8-week follow-up, fasting glucose is 184 mg/dL and HbA1c has risen from 5.6% to 7.4%; she was previously normoglycemic. She has no prior diabetes and is not obese. Which of the following best explains the mechanism of her new hyperglycemia and identifies the most mechanistically appropriate first-line pharmacologic management?
A) Pasireotide's potent SSTR5 agonism on pancreatic beta cells suppresses glucose-stimulated insulin secretion, producing hyperglycemia; because the defect is impaired insulin secretion via a cAMP-dependent step, a GLP-1 receptor agonist (which raises beta-cell cAMP through a pathway that bypasses the somatostatin-inhibited signaling) is a mechanistically appropriate first-line therapy
B) The hyperglycemia reflects new-onset autoimmune type 1 diabetes coincidentally unmasked by pasireotide; insulin is required immediately and no oral agent will be effective
C) Pasireotide causes hyperglycemia by stimulating hepatic gluconeogenesis through SSTR2-mediated glucagon release; a sulfonylurea is the most appropriate first-line therapy because it directly opposes glucagon
D) The hyperglycemia is due to pasireotide-induced insulin resistance in skeletal muscle from SSTR3 activation; metformin is mechanistically required because it reverses this specific receptor-mediated resistance
E) The glucose elevation is an artifact of the assay caused by pasireotide cross-reactivity and requires no treatment, only reassurance and repeat testing in 6 months
ANSWER: A
Rationale:
This question asked you to identify the mechanism of pasireotide-induced hyperglycemia and the most mechanistically appropriate management. Pasireotide is a pan-somatostatin-receptor agonist with high affinity for SSTR5. Pancreatic beta cells express SSTR5, and its activation inhibits adenylyl cyclase (Gi coupling), lowering cAMP and suppressing glucose-stimulated insulin secretion. The dominant defect is therefore impaired insulin secretion (not insulin resistance), and clinical data show hyperglycemia in roughly 73% of pasireotide-treated patients. Because the lesion is a cAMP-dependent suppression of insulin release, GLP-1 receptor agonists — which raise beta-cell cAMP through a receptor pathway that bypasses the somatostatin-inhibited step — are particularly effective and are favored first-line, along with DPP-4 inhibitors; metformin is often added but does not directly address the secretory defect.
Option B: Option B is incorrect because the hyperglycemia is a predictable pharmacologic effect of SSTR5-mediated insulin suppression, not autoimmune type 1 diabetes; many patients respond to incretin-based oral therapy rather than requiring immediate insulin.
Option C: Option C is incorrect because somatostatin analogs suppress (not stimulate) glucagon via SSTR2; the hyperglycemia is driven by impaired insulin secretion, and a sulfonylurea is not the most mechanistically appropriate first choice given the cAMP-dependent secretory defect that incretin therapy targets directly.
Option D: Option D is incorrect because the principal mechanism is impaired insulin secretion via beta-cell SSTR5, not SSTR3-mediated skeletal muscle insulin resistance; metformin addresses hepatic glucose output and insulin sensitivity but does not reverse a receptor-mediated secretory defect.
Option E: Option E is incorrect because the glucose elevation is real and mechanistically expected, not an assay artifact; ignoring a rising HbA1c would be inappropriate.
3. A 29-year-old woman with schizophrenia, stable on risperidone, develops amenorrhea, galactorrhea, and reduced libido. Serum prolactin is 110 ng/mL (markedly elevated); pregnancy test is negative, TSH is normal, and MRI shows no pituitary adenoma. Her psychiatrist wants to address the hyperprolactinemia while maintaining antipsychotic control. Which of the following pharmacologic strategies is most mechanistically sound?
A) Add a dopamine D2 receptor antagonist such as metoclopramide to compete with risperidone at the lactotroph and normalize prolactin
B) Increase the risperidone dose, because higher D2 receptor blockade in the pituitary will eventually downregulate prolactin secretion
C) Add bromocriptine at high dose and continue full-dose risperidone indefinitely, accepting that the dopamine agonist will fully override pituitary D2 blockade without affecting psychiatric stability
D) Switch to (or augment with) aripiprazole, a partial D2 receptor agonist that provides sufficient dopaminergic tone at the pituitary lactotroph to suppress prolactin while retaining functional antagonism in mesolimbic pathways for antipsychotic efficacy; aripiprazole can normalize prolactin even when added to a prolactin-elevating antipsychotic
E) Discontinue all antipsychotic therapy permanently, since hyperprolactinemia indicates that the patient can no longer tolerate any dopaminergic-active medication
ANSWER: D
Rationale:
This question asked you to select the most mechanistically sound strategy for risperidone-induced hyperprolactinemia while maintaining antipsychotic control. Risperidone is a potent D2 receptor antagonist that elevates prolactin by removing dopaminergic inhibition at the pituitary lactotroph. Aripiprazole is a partial D2 receptor agonist: at the pituitary, where dopamine tone is physiologically present, its partial agonism provides enough D2R activation to suppress prolactin, while in mesolimbic pathways its partial agonism functions as functional antagonism sufficient for antipsychotic efficacy. Clinically, switching to aripiprazole — or adding low-dose aripiprazole to the existing regimen — can normalize prolactin even in patients on a prolactin-elevating antipsychotic, making it the preferred mechanistic solution.
Option A: Option A is incorrect because metoclopramide is itself a D2 receptor antagonist that elevates prolactin; adding it would worsen, not correct, the hyperprolactinemia.
Option B: Option B is incorrect because increasing the risperidone dose increases D2 blockade and would raise prolactin further; D2 antagonism does not downregulate prolactin secretion over time.
Option C: Option C is incorrect because adding a dopamine agonist (bromocriptine) to a full-dose D2 antagonist is mechanistically self-defeating and risks destabilizing the psychiatric illness by opposing the antipsychotic's intended dopamine blockade in mesolimbic pathways; this is not the preferred strategy.
Option E: Option E is incorrect because hyperprolactinemia does not require permanent discontinuation of all antipsychotic therapy; it is managed by selecting a prolactin-sparing agent such as aripiprazole, preserving needed psychiatric treatment.
4. A 35-year-old man develops polyuria (8 L/day) and severe thirst 2 days after transsphenoidal resection of a craniopharyngioma. Serum sodium is 149 mEq/L, serum osmolality is elevated, and urine is inappropriately dilute. A water deprivation test followed by administration of desmopressin produces a robust increase in urine osmolality. Which of the following best explains the diagnosis and the pharmacologic basis for the desmopressin response?
A) The diagnosis is nephrogenic diabetes insipidus; the urine concentrates after desmopressin because the renal collecting duct V2 receptors are hypersensitive following surgery
B) The diagnosis is central (neurogenic) diabetes insipidus from surgical disruption of hypothalamic-posterior pituitary vasopressin production; urine osmolality rises after desmopressin because the renal collecting duct V2 receptors and aquaporin-2 machinery are intact and respond to the exogenous V2 agonist, distinguishing central from nephrogenic diabetes insipidus
C) The diagnosis is primary polydipsia; the desmopressin response confirms psychogenic water intake as the cause of the polyuria
D) The diagnosis is osmotic diuresis from postoperative hyperglycemia; desmopressin concentrates the urine by directly reducing the filtered glucose load
E) The diagnosis is SIADH; the urine concentrates after desmopressin because exogenous vasopressin adds to the already excessive endogenous antidiuretic hormone activity
ANSWER: B
Rationale:
This question asked you to interpret a water deprivation/desmopressin test in a postoperative patient and explain the pharmacologic basis of the response. This patient has central (neurogenic) diabetes insipidus: surgical manipulation near the hypothalamus and posterior pituitary disrupted vasopressin (ADH) production, producing polyuria, hypernatremia, elevated serum osmolality, and inappropriately dilute urine. The defining pharmacologic feature is that the renal collecting duct apparatus — V2 receptors and aquaporin-2 water channels — remains intact; administering desmopressin (a selective V2 agonist) therefore drives aquaporin-2 insertion and produces a robust rise in urine osmolality. This response distinguishes central diabetes insipidus (ADH-deficient but renally responsive) from nephrogenic diabetes insipidus (renally unresponsive, where urine fails to concentrate after desmopressin).
Option A: Option A is incorrect because in nephrogenic diabetes insipidus the kidney does not respond to desmopressin — urine fails to concentrate; a robust concentrating response excludes nephrogenic diabetes insipidus and points to a central cause.
Option C: Option C is incorrect because primary polydipsia is a chronic condition that does not typically present acutely after pituitary surgery with hypernatremia; the clinical context and hypernatremia indicate a true ADH deficiency, not psychogenic water intake.
Option D: Option D is incorrect because osmotic diuresis from hyperglycemia produces glucosuria and would not be corrected by desmopressin, which acts on water handling, not the filtered glucose load.
Option E: Option E is incorrect because SIADH causes water retention and hyponatremia, the opposite of this patient's hypernatremia and dilute urine; giving desmopressin in SIADH would worsen water retention, and the clinical picture here is diabetes insipidus, not SIADH.
5. A 64-year-old woman with small cell lung cancer has euvolemic hyponatremia (serum sodium 118 mEq/L) with concentrated urine, elevated urine sodium, and clinical features consistent with SIADH. She is confused but not seizing. Fluid restriction has been inadequate, and the team initiates tolvaptan. Which of the following best describes tolvaptan's mechanism and the single most important monitoring concern during its initiation?
A) Tolvaptan is a V2 receptor agonist that enhances aquaporin-2 insertion; the principal concern is worsening hyponatremia from excessive water retention
B) Tolvaptan is a V1a receptor antagonist that produces vasodilation; the principal concern is hypotension during initiation
C) Tolvaptan is a somatostatin analog that suppresses tumor ADH production; the principal concern is hyperglycemia from beta-cell suppression
D) Tolvaptan is an oxytocin receptor antagonist used off-label for hyponatremia; the principal concern is uterine atony in women of reproductive age
E) Tolvaptan is a selective V2 receptor antagonist that blocks vasopressin-stimulated aquaporin-2 insertion in the renal collecting duct, producing a free water diuresis (aquaresis) that raises serum sodium; the single most important concern is overly rapid correction of sodium, which risks osmotic demyelination syndrome, so the rate of sodium rise must be closely monitored and fluid restriction relaxed during therapy
ANSWER: E
Rationale:
This question asked you to identify tolvaptan's mechanism and the key monitoring concern in treating SIADH. Tolvaptan is a selective vasopressin V2 receptor antagonist. By blocking V2 receptors on renal collecting duct principal cells, it prevents vasopressin-stimulated aquaporin-2 insertion, producing a free water diuresis (aquaresis) — excretion of water without proportional electrolyte loss — which raises serum sodium and corrects the dilutional hyponatremia of SIADH. The single most important concern during initiation is overly rapid correction of sodium: raising sodium too quickly (generally more than 8 to 10 mEq/L in 24 hours) risks osmotic demyelination syndrome (central pontine myelinolysis). Therefore the sodium rise must be monitored closely, fluid restriction is typically relaxed during tolvaptan therapy to avoid additive overcorrection, and tolvaptan is initiated in a monitored setting.
Option A: Option A is incorrect because tolvaptan is a V2 antagonist (not an agonist); it promotes water excretion and raises sodium, so worsening hyponatremia from water retention is not its effect.
Option B: Option B is incorrect because tolvaptan is a V2 antagonist, not a V1a antagonist; it does not act primarily as a vasodilator, and hypotension is not its principal initiation concern.
Option C: Option C is incorrect because tolvaptan is not a somatostatin analog and does not suppress tumor ADH production; it blocks the renal V2 receptor, and hyperglycemia is not its mechanism or concern.
Option D: Option D is incorrect because tolvaptan is a vasopressin V2 antagonist, not an oxytocin receptor antagonist; uterine atony is not a relevant concern, and the overcorrection risk is the dominant safety issue.
6. A 31-year-old woman with endometriosis-associated pelvic pain has been well controlled on elagolix for 6 months. She is newly diagnosed with epilepsy and started on a strong CYP3A4 inducer for seizure control. Over the following weeks, her pelvic pain returns to near-baseline severity despite continued elagolix adherence. Which of the following best explains the loss of efficacy and the most appropriate next step?
A) The CYP3A4 inducer has accelerated elagolix metabolism, lowering its plasma concentration and reducing its suppression of the hypothalamic-pituitary-gonadal axis, allowing estrogen-driven endometriosis pain to recur; the interaction should be addressed by reassessing the anticonvulsant choice or the GnRH-axis therapy rather than simply assuming disease progression
B) The CYP3A4 inducer has inhibited elagolix metabolism, raising its plasma concentration and causing receptor desensitization that paradoxically restores estrogen production
C) The recurrence proves elagolix has intrinsically stopped working due to tachyphylaxis at the GnRH receptor, and the anticonvulsant is irrelevant to the loss of effect
D) The anticonvulsant has displaced elagolix from plasma protein binding sites, increasing its clearance and requiring a lower elagolix dose to restore efficacy
E) The CYP3A4 inducer has converted elagolix into an active GnRH agonist metabolite that now stimulates rather than suppresses the axis, accounting for the recurrence of symptoms
ANSWER: A
Rationale:
This question asked you to apply elagolix pharmacokinetics to a drug-interaction scenario causing loss of efficacy. Elagolix is a non-peptide oral GnRH antagonist metabolized predominantly by CYP3A4. A strong CYP3A4 inducer increases hepatic CYP3A4 activity, accelerating elagolix metabolism and lowering its plasma concentration. Reduced elagolix exposure means less suppression of the hypothalamic-pituitary-gonadal axis, so estrogen production rises and estrogen-dependent endometriosis pain recurs — exactly the pattern described. The appropriate response is to recognize the interaction and address it: reassess the anticonvulsant choice (selecting a non-inducing agent if feasible) or reconsider the GnRH-axis therapy, rather than assuming the endometriosis has simply progressed.
Option B: Option B is incorrect because a CYP3A4 inducer accelerates (not inhibits) elagolix metabolism, lowering rather than raising its concentration; the mechanism described is the opposite of an inducer's effect.
Option C: Option C is incorrect because the loss of effect is explained by the drug interaction, not intrinsic tachyphylaxis; the anticonvulsant is directly relevant as the cause of reduced elagolix exposure.
Option D: Option D is incorrect because the dominant interaction is CYP3A4 induction increasing metabolism, not plasma protein-binding displacement; and increasing clearance via induction would not be corrected by simply lowering the dose.
Option E: Option E is incorrect because elagolix is not converted into an active GnRH agonist metabolite; it is a GnRH antagonist whose CYP3A4 metabolism yields inactive metabolites, so induction reduces active drug rather than generating a stimulatory agonist.
7. A 58-year-old man with a metastatic midgut neuroendocrine tumor and carcinoid syndrome (flushing and secretory diarrhea) is started on octreotide LAR, with marked improvement in his symptoms. At a follow-up visit several months later, he is counseled about adverse effects associated with chronic somatostatin analog therapy. Which of the following correctly pairs octreotide's symptom-controlling mechanism with a predictable adverse effect of chronic therapy?
A) Octreotide controls carcinoid symptoms by stimulating serotonin release from tumor cells; the predictable adverse effect is serotonin syndrome
B) Octreotide controls carcinoid symptoms by antagonizing peripheral histamine receptors; the predictable adverse effect is sedation from central histamine blockade
C) Octreotide controls carcinoid symptoms primarily through SSTR2-mediated suppression of tumor secretory products (such as serotonin and vasoactive peptides) and reduced gut secretion and motility; a predictable adverse effect of chronic therapy is cholelithiasis (gallstones), because reduced gallbladder contractility and altered bile composition promote stone formation, and hyperglycemia can also occur from suppressed insulin secretion
D) Octreotide controls carcinoid symptoms by blocking V2 receptors in the gut; the predictable adverse effect is hypernatremia from renal water loss
E) Octreotide controls carcinoid symptoms by enhancing gastrointestinal motility through SSTR5 agonism; the predictable adverse effect is chronic diarrhea from accelerated transit
ANSWER: C
Rationale:
This question asked you to pair octreotide's mechanism of carcinoid symptom control with a predictable adverse effect of chronic use. Octreotide is an SSTR2/SSTR5-selective somatostatin analog; in carcinoid syndrome it acts mainly through SSTR2-mediated suppression of the tumor's secretory products (serotonin and vasoactive peptides) and through broad inhibition of gut secretion and motility, relieving flushing and secretory diarrhea. The same broad inhibitory action produces predictable adverse effects: reduced gallbladder contractility and altered bile composition promote cholelithiasis (gallstones) with chronic therapy, and suppression of pancreatic insulin secretion can cause hyperglycemia. Gallstone formation is one of the most characteristic long-term adverse effects of somatostatin analog therapy.
Option A: Option A is incorrect because octreotide suppresses (not stimulates) tumor serotonin release; it does not cause serotonin syndrome, and serotonin suppression is part of its therapeutic benefit.
Option B: Option B is incorrect because octreotide does not act by antagonizing histamine receptors and does not cause central histamine-blockade sedation; its action is somatostatin-receptor agonism.
Option D: Option D is incorrect because octreotide is not a V2 receptor blocker and does not control carcinoid symptoms through renal water handling; hypernatremia is not its mechanism or characteristic adverse effect.
Option E: Option E is incorrect because octreotide suppresses (not enhances) gastrointestinal motility, reducing diarrhea in carcinoid syndrome; it does not accelerate transit, and SSTR activation is inhibitory rather than motility-enhancing.
8. A 44-year-old woman has confirmed ACTH-dependent Cushing syndrome (elevated cortisol, non-suppressed ACTH). Pituitary MRI shows no definite adenoma. She undergoes inferior petrosal sinus sampling (IPSS) with CRH stimulation. After CRH administration, the central (petrosal) ACTH greatly exceeds the simultaneous peripheral ACTH, and the central ACTH rises markedly with CRH. Which of the following best interprets these findings and explains the underlying pharmacologic principle?
A) The high peripheral-to-central ACTH ratio indicates an ectopic ACTH source, because ectopic tumors secrete ACTH directly into the systemic circulation and respond briskly to CRH
B) A central-to-peripheral ACTH gradient that increases after CRH stimulation indicates a pituitary (corticotroph adenoma) source of ACTH, because pituitary corticotrophs drain into the inferior petrosal sinuses and retain CRH-R1 responsiveness, whereas ectopic ACTH sources do not produce a central gradient and typically do not respond to CRH
C) The findings indicate adrenal Cushing syndrome, because autonomous adrenal cortisol production drives the central ACTH gradient seen on IPSS
D) The CRH-stimulated central gradient is a nonspecific finding present in all causes of Cushing syndrome and cannot localize the ACTH source
E) The findings indicate primary polydipsia-associated pseudo-Cushing, because CRH stimulation normalizes ACTH secretion in functional hypercortisolism
ANSWER: B
Rationale:
This question asked you to interpret inferior petrosal sinus sampling with CRH stimulation in ACTH-dependent Cushing syndrome. The inferior petrosal sinuses drain the pituitary, so sampling ACTH there and comparing it with simultaneous peripheral ACTH localizes the source. A central (petrosal)-to-peripheral ACTH gradient — especially one that increases after CRH stimulation — indicates a pituitary corticotroph adenoma (Cushing disease): pituitary corticotrophs drain into the petrosal sinuses and retain CRH-R1 responsiveness, so CRH amplifies the central gradient. Ectopic ACTH-secreting tumors, by contrast, secrete into the systemic circulation without producing a central gradient and typically do not respond to CRH (they usually lack functional CRH-R1). IPSS with CRH is therefore the gold standard for distinguishing pituitary from ectopic ACTH when MRI is non-diagnostic.
Option A: Option A is incorrect because the described finding is a high central-to-peripheral gradient (central exceeds peripheral), which indicates a pituitary source; a high peripheral-relative-to-central pattern with no central gradient would suggest an ectopic source.
Option C: Option C is incorrect because adrenal Cushing syndrome is ACTH-independent (ACTH is suppressed), so it would not produce an ACTH gradient on IPSS; the case specifies ACTH-dependent disease.
Option D: Option D is incorrect because the CRH-stimulated central gradient is not nonspecific — it specifically localizes the ACTH source to the pituitary, which is the diagnostic purpose of the test.
Option E: Option E is incorrect because the patient has confirmed ACTH-dependent Cushing syndrome with a clear central gradient, not pseudo-Cushing; IPSS findings of this kind are not explained by primary polydipsia.
9. A 28-year-old woman at 41 weeks gestation undergoes labor induction with a high-dose intravenous oxytocin infusion run in a large volume of hypotonic dextrose solution over many hours. She becomes confused and develops a serum sodium of 122 mEq/L. Which of the following best explains the mechanism of her hyponatremia?
A) High-dose oxytocin directly inhibits renal sodium reabsorption in the proximal tubule, causing renal salt wasting and hyponatremia
B) Oxytocin stimulates aldosterone secretion, driving potassium retention and a dilutional fall in sodium
C) The hyponatremia is unrelated to oxytocin and reflects the physiologic hemodilution of normal pregnancy
D) At high infusion rates, oxytocin exhibits cross-activity at renal vasopressin V2 receptors (its structural similarity to vasopressin), producing an antidiuretic effect; combined with administration of large volumes of hypotonic fluid, this water retention causes dilutional hyponatremia (oxytocin-induced water intoxication)
E) Oxytocin antagonizes V2 receptors in the collecting duct, producing a free water diuresis that paradoxically lowers serum sodium through excessive solute loss
ANSWER: D
Rationale:
This question asked you to explain hyponatremia developing during high-dose oxytocin labor induction. Oxytocin and vasopressin are structurally similar nonapeptides, and at high infusion rates oxytocin exhibits cross-activity at renal vasopressin V2 receptors. V2 activation drives aquaporin-2 insertion in the collecting duct, producing an antidiuretic effect (water retention). When high-dose oxytocin is combined with administration of large volumes of hypotonic fluid (such as hypotonic dextrose), the retained free water dilutes serum sodium, producing dilutional hyponatremia — classically described as oxytocin-induced water intoxication, which can cause confusion, seizures, and in severe cases cerebral edema. Prevention involves using isotonic fluids and avoiding unnecessarily high oxytocin infusion rates and volumes.
Option A: Option A is incorrect because oxytocin does not act on the proximal tubule to inhibit sodium reabsorption; the hyponatremia is dilutional from V2-mediated water retention, not renal salt wasting.
Option B: Option B is incorrect because oxytocin's hyponatremia is not mediated by aldosterone stimulation; the mechanism is antidiuretic water retention via V2 cross-activity, not mineralocorticoid-driven electrolyte shifts.
Option C: Option C is incorrect because a serum sodium of 122 mEq/L with confusion is pathologic, not the mild physiologic hemodilution of pregnancy; the clinical setting points directly to oxytocin-induced water intoxication.
Option E: Option E is incorrect because oxytocin at high doses acts as a V2 agonist (cross-activity), producing antidiuresis and water retention, not V2 antagonism with free water diuresis; the option inverts the mechanism.
10. A 75-year-old man with prostate cancer is maintained on oral relugolix for androgen deprivation. He is hospitalized for atrial fibrillation and started on a strong P-glycoprotein (P-gp) inhibitor. The pharmacist flags the combination. Which of the following best explains the concern and the most appropriate management?
A) The P-gp inhibitor will accelerate relugolix elimination, lowering its plasma concentration and risking loss of androgen suppression; the relugolix dose should be increased
B) The P-gp inhibitor will induce hepatic CYP3A4, increasing relugolix metabolism and necessitating a higher relugolix dose to maintain testosterone suppression
C) The combination is of no concern because relugolix is eliminated unchanged by the kidney and does not interact with P-gp
D) The P-gp inhibitor displaces relugolix from albumin, transiently increasing free drug but with no net change in total exposure or clinical effect
E) Relugolix is a substrate of the intestinal efflux transporter P-glycoprotein (P-gp); a strong P-gp inhibitor reduces efflux of relugolix back into the gut lumen during absorption, markedly increasing relugolix plasma exposure; the labeling advises avoiding co-administration with strong P-gp inhibitors when possible, or using strategies such as separating dose timing and close monitoring, because excessive exposure can deepen axis suppression and is a recognized interaction concern
ANSWER: E
Rationale:
This question asked you to identify the relugolix–P-gp inhibitor interaction and its management. Relugolix is a substrate of the intestinal efflux transporter P-glycoprotein (P-gp), which normally pumps a portion of absorbed relugolix back into the gut lumen, limiting its bioavailability (oral bioavailability is only about 12%). A strong P-gp inhibitor reduces this efflux, allowing more relugolix to be absorbed and markedly increasing its plasma exposure. Because excessive exposure can deepen hypothalamic-pituitary-gonadal axis suppression and raise other safety concerns, the relugolix labeling advises avoiding co-administration with strong oral P-gp inhibitors when possible; when the combination is unavoidable, recommended strategies include separating the timing of administration and close monitoring.
Option A: Option A is incorrect because a P-gp inhibitor reduces efflux and raises (not lowers) relugolix exposure; increasing the dose would compound the overexposure and is the opposite of appropriate management.
Option B: Option B is incorrect because the dominant interaction is at intestinal P-gp, not CYP3A4 induction; P-gp inhibitors do not induce CYP3A4, and the net effect is increased, not decreased, relugolix exposure.
Option C: Option C is incorrect because relugolix is not eliminated unchanged by the kidney and does interact significantly with P-gp; the interaction is clinically important, not negligible.
Option D: Option D is incorrect because the principal mechanism is reduced intestinal P-gp efflux increasing absorption, not plasma protein-binding displacement; the interaction produces a real increase in total relugolix exposure.
11. A 33-year-old woman presents with a 4-month history of galactorrhea and irregular menses. She reports fatigue, cold intolerance, weight gain, and constipation. Laboratory testing shows TSH 88 mIU/L, free T4 markedly low, and prolactin 65 ng/mL (moderately elevated). Pituitary MRI shows symmetric mild pituitary enlargement without a discrete adenoma. Which of the following is the most appropriate initial management, and what is the underlying mechanism?
A) Start cabergoline to lower the prolactin and refer for transsphenoidal surgery to resect the enlarged pituitary, since the imaging indicates a prolactinoma requiring intervention
B) Start levothyroxine to treat the primary hypothyroidism; the hyperprolactinemia is driven by chronically elevated TRH (from absent thyroid hormone negative feedback) stimulating lactotrophs via the TRH receptor, and the reactive pituitary enlargement is thyrotroph and lactotroph hyperplasia — both the prolactin elevation and the pituitary enlargement are expected to resolve as thyroid hormone is replaced, without prolactin-directed therapy or surgery
C) Start a somatostatin analog to suppress prolactin and shrink the pituitary, since somatostatin is the primary inhibitor of prolactin secretion
D) Begin combined oral contraceptives to regulate menses and treat the galactorrhea directly, deferring evaluation of the abnormal thyroid studies as incidental
E) Refer urgently for pituitary irradiation, since the combination of pituitary enlargement and hyperprolactinemia indicates an aggressive pituitary tumor unlikely to respond to medical therapy
ANSWER: B
Rationale:
This question asked you to manage a patient with hyperprolactinemia and galactorrhea in the setting of severe primary hypothyroidism. The correct initial step is levothyroxine to treat the underlying hypothyroidism. In severe primary hypothyroidism, the loss of thyroid hormone negative feedback drives chronically elevated TRH; because the TRH receptor is expressed on lactotrophs as well as thyrotrophs, the high TRH stimulates prolactin secretion, producing the hyperprolactinemia and galactorrhea. Chronic thyrotroph and lactotroph stimulation also causes reactive pituitary hyperplasia that appears as symmetric pituitary enlargement on MRI, mimicking an adenoma. Restoring thyroid hormone re-establishes negative feedback, lowers TRH drive, and resolves both the hyperprolactinemia and the pituitary enlargement — without prolactin-directed therapy or surgery. Recognizing this avoids unnecessary intervention.
Option A: Option A is incorrect because the pituitary enlargement is reactive hyperplasia driven by TRH, not a prolactinoma; cabergoline and surgery are unnecessary, and treating the hypothyroidism resolves the findings.
Option C: Option C is incorrect because somatostatin is not the primary inhibitor of prolactin (dopamine is), and somatostatin analogs are not the treatment for this TRH-driven hyperprolactinemia; levothyroxine is the appropriate therapy.
Option D: Option D is incorrect because the abnormal thyroid studies are the cause of the presentation, not an incidental finding; deferring their evaluation and merely masking symptoms with oral contraceptives would miss the underlying severe hypothyroidism.
Option E: Option E is incorrect because the imaging reflects benign reactive hyperplasia, not an aggressive tumor; pituitary irradiation is not indicated, and the condition responds to thyroid hormone replacement.
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