1. A 62-year-old man with major depressive disorder on sertraline 150 mg daily is admitted for a methicillin-resistant Staphylococcus aureus (MRSA) wound infection and started on linezolid 600 mg IV every 12 hours by the infectious disease team. On day 3 of linezolid therapy he becomes agitated, develops diaphoresis, and is noted to have inducible clonus at both ankles and brisk hyperreflexia throughout. His temperature is 38.9 degrees Celsius and heart rate is 112. Which of the following is the most appropriate immediate management?
A) Continue both sertraline and linezolid at current doses but add haloperidol 2 mg IV for the agitation, and repeat neurological examination in 4 hours to determine whether escalation is needed
B) Discontinue sertraline only and continue linezolid because the antibacterial treatment for MRSA cannot be interrupted; administer oral cyproheptadine 12 mg loading dose as definitive treatment and monitor
C) Discontinue both sertraline and linezolid immediately, administer intravenous benzodiazepines for agitation and neuromuscular hyperactivity, arrange active cooling measures, and consult infectious disease urgently for an alternative non-serotonergic MRSA antibiotic such as daptomycin or vancomycin
D) Discontinue linezolid and continue sertraline, as the serotonergic risk came entirely from the antibiotic; administer dantrolene intravenously to block the ryanodine receptor-mediated component of the hyperthermia
E) Reduce sertraline to 50 mg daily and reduce linezolid to once-daily dosing; both drugs can be continued at lower doses because the interaction is concentration-dependent and half-dose levels will not produce serotonin syndrome
ANSWER: C
Rationale:
This question asked you to manage an evolving serotonin syndrome caused by the well-recognized linezolid-SSRI interaction. Linezolid has monoamine oxidase inhibitor properties that combine with sertraline's SERT blockade to produce excess serotonergic stimulation — a pharmacodynamic interaction independent of drug concentrations. This patient meets Hunter Criteria for serotonin syndrome: serotonergic agents in history (linezolid with MAO inhibitor activity plus sertraline) plus inducible clonus with agitation. The correct immediate response is to remove both contributing agents simultaneously. Continuing linezolid while stopping only sertraline is inadequate because linezolid's MAO inhibitor activity persists until it is also discontinued. Alternative MRSA antibiotics without serotonergic activity — daptomycin, vancomycin, or trimethoprim-sulfamethoxazole depending on sensitivities — should be substituted urgently. Intravenous benzodiazepines are first-line for the agitation and neuromuscular hyperactivity, which generate heat through sustained muscular activity. Active cooling addresses the hyperthermia.
Option A:
Option A: Option A is incorrect because continuing both serotonergic agents while adding haloperidol addresses neither the mechanism nor the source of the toxicity; haloperidol does not treat serotonin syndrome and its dopamine D2 blockade is mechanistically irrelevant to the excess 5-HT receptor activation driving this presentation; the correct approach is removal of the precipitating agents, not addition of a dopaminergic antagonist.
Option B:
Option B: Option B is incorrect because discontinuing only sertraline while continuing linezolid is inadequate; linezolid itself has MAO inhibitor properties that continue to impair serotonin degradation even without sertraline; the interaction requires removal of both contributing agents; oral cyproheptadine alone is insufficient for a patient with agitation and evolving neuromuscular hyperactivity who may not be able to reliably swallow tablets.
Option D:
Option D: Option D is incorrect because the hyperthermia in serotonin syndrome is generated by sustained muscular contraction driven by excess serotonergic receptor activation, not by ryanodine receptor-mediated dysregulated calcium release as in malignant hyperthermia; dantrolene targets the ryanodine receptor and is not a standard treatment for serotonin syndrome; continuing sertraline while stopping only linezolid also incompletely addresses the interaction.
Option E:
Option E: Option E is incorrect because the linezolid-sertraline interaction is pharmacodynamic — driven by combined MAO inhibition plus SERT blockade — and is not simply concentration-dependent in a way that can be managed by dose reduction; lowering doses of both agents does not eliminate the interaction mechanism, and continuing both drugs in a patient who has already developed serotonin syndrome is clinically dangerous.
2. A 54-year-old woman with treatment-resistant depression on phenelzine 45 mg daily presents to the emergency department 45 minutes after eating at a restaurant where she consumed a large portion of aged cheese. Her blood pressure is 238/142 mmHg, heart rate 108, and she reports a severe throbbing occipital headache. She appears diaphoretic and anxious. There is no clonus on neurological examination. An ECG shows sinus tachycardia without QTc prolongation. Which of the following is the most appropriate initial pharmacological management of her blood pressure?
A) Labetalol 20 mg intravenously, because combined alpha and beta blockade lowers both cardiac output and peripheral vascular resistance, addressing all components of the hypertensive surge
B) Metoprolol 5 mg intravenously, because selective beta-1 blockade reduces the cardiac output and heart rate components of the sympathomimetic response without affecting peripheral resistance
C) Sodium nitroprusside infusion, because it is the most potent and titratable vasodilator available and is first-line for all hypertensive emergencies regardless of mechanism
D) Clonidine 0.2 mg orally, because central alpha-2 agonism reduces brainstem sympathetic outflow and is the most rapid-acting oral agent for hypertensive urgency in this setting
E) Phentolamine 5 mg intravenously, because it is a non-selective alpha-adrenergic antagonist that directly reverses the alpha-1-mediated vasoconstriction produced by the massive norepinephrine release that tyramine triggered from adrenergic nerve terminals
ANSWER: E
Rationale:
This question asked you to identify the mechanism-targeted treatment for the tyramine-MAOI hypertensive crisis. The pathophysiology is indirect sympathomimesis: dietary tyramine was absorbed intact because phenelzine's irreversible MAO-A inhibition eliminated first-pass gut and liver tyramine catabolism; tyramine entered adrenergic nerve terminals via the norepinephrine transporter, displaced vesicular norepinephrine into the synapse, and the massive resulting norepinephrine release activated alpha-1 adrenergic receptors on vascular smooth muscle, causing the acute severe hypertension. Phentolamine is a non-selective alpha-adrenergic antagonist that directly competes with norepinephrine at the alpha-1 receptor, reversing the vasoconstriction at its receptor-level source. The absence of clonus and hyperreflexia makes serotonin syndrome unlikely — this is a pure catecholamine-mediated hypertensive crisis, not a serotonergic event. Sublingual nifedipine is an alternative.
Option A:
Option A: Option A is incorrect because labetalol's beta-blocking component carries a theoretical risk in the tyramine-MAOI crisis: beta-2 receptor blockade removes a vasodilatory counterbalance while massive alpha-1 stimulation from released norepinephrine remains partially unopposed; selective alpha blockade is the preferred mechanistic approach, and phentolamine's pure alpha antagonism avoids this concern.
Option B:
Option B: Option B is incorrect because selective beta-1 blockade with metoprolol addresses only the cardiac rate and output components of the hypertensive crisis without blocking the dominant alpha-1-mediated peripheral vasoconstriction; using a pure beta-blocker in a state of massive unblocked alpha-1 receptor activation risks leaving the peripheral vasoconstriction component entirely untreated and could paradoxically worsen hypertension.
Option C:
Option C: Option C is incorrect not because sodium nitroprusside is ineffective — it is a potent vasodilator — but because it acts through a receptor-independent mechanism (direct NO-mediated guanylate cyclase activation) that does not specifically target the alpha-1 adrenergic pathway driving this crisis; phentolamine is mechanistically preferred for the tyramine-MAOI interaction because it addresses the causal receptor directly; nitroprusside also requires intensive ICU monitoring for cyanide toxicity and is not first-line for this specific indication.
Option D:
Option D: Option D is incorrect because the tyramine-MAOI crisis is a peripheral sympathomimetic event driven by direct norepinephrine release from nerve terminals, not by increased central sympathetic outflow; clonidine reduces centrally generated sympathetic tone but cannot effectively reverse the peripheral alpha-1 receptor activation already occurring from the massive norepinephrine already released; clonidine's onset is also too slow for an acute hypertensive emergency requiring rapid blood pressure reduction.
3. A 71-year-old man with major depressive disorder that failed three oral antidepressants was started on the selegiline transdermal patch 9 mg/24 hours six weeks ago. He presents to the emergency department with a blood pressure of 208/126 mmHg and severe headache after eating aged Camembert cheese at a family dinner. His Parkinson-disease-free neurological examination is otherwise unremarkable. He tells you he was never counseled about any dietary restrictions because "selegiline doesn't need them." Which of the following best explains why this patient developed a tyramine-related hypertensive crisis despite being on selegiline rather than phenelzine?
A) At the 9 mg/24 hour transdermal dose used for antidepressant effect, selegiline achieves systemic levels sufficient to inhibit not only MAO-B but also MAO-A — including MAO-A in the gut and liver responsible for first-pass tyramine catabolism; the no-restriction rule applies only to the low oral doses used in Parkinson disease, where MAO-B selectivity is preserved
B) The transdermal route converts selegiline from a selective MAO-B inhibitor to a non-selective MAO inhibitor through a metabolic activation step that only occurs in skin; the active skin metabolite irreversibly inhibits both MAO-A and MAO-B, which does not occur with oral selegiline at any dose
C) Selegiline at all doses and by all routes is a selective MAO-B inhibitor; this patient's hypertensive crisis was caused by an unrelated mechanism — the aged cheese contained a large amount of tyramine that overwhelmed normal MAO-A capacity even in the absence of any MAO inhibition
D) The transdermal patch formulation has a different chemical structure from oral selegiline due to manufacturing modifications; the patch delivers a distinct molecular entity that is pharmacologically non-selective for MAO isoforms, regardless of dose
E) All transdermal selegiline formulations at all patch doses require tyramine restriction because transdermal delivery inherently bypasses all MAO-A-mediated first-pass catabolism of the drug itself, producing an MAO-A inhibitory metabolite that accumulates in the intestinal mucosa
ANSWER: A
Rationale:
This question asked you to apply the dose-dependent pharmacology of selegiline to a clinical case where the treating team failed to counsel appropriately. At low oral doses used for Parkinson disease (up to 10 mg per day), selegiline is selective for MAO-B. MAO-B inhibition provides antiparkinsonian benefit by reducing dopamine catabolism in the striatum. At these doses, gut and liver MAO-A remains substantially intact, metabolizing dietary tyramine during first-pass and preventing its systemic absorption. This is why the Parkinson dose does not require tyramine dietary restriction. However, the selegiline transdermal patch at 9 mg/24 hours — used for its FDA-approved antidepressant indication — delivers systemic selegiline at levels sufficient to produce meaningful MAO-A inhibition throughout the body, including in the gut mucosa and liver. At these higher systemic exposures, selegiline loses its MAO-B selectivity. The prescribing information for the selegiline patch explicitly recommends dietary tyramine restriction at the 9 mg/24 hr and 12 mg/24 hr doses; only the 6 mg/24 hr starting dose carries a weaker recommendation. This patient's clinician failed to communicate this dose-dependent restriction.
Option B:
Option B: Option B is incorrect because there is no pharmacologically active skin metabolite of selegiline that switches its isoform selectivity; the dose-dependence of selegiline's MAO-B to non-selective transition is determined by systemic drug concentration, not by a route-specific metabolic activation step occurring in skin.
Option C:
Option C: Option C is incorrect because selegiline's selectivity is explicitly dose-dependent and is lost at higher systemic exposures; at the 9 mg/24 hr transdermal dose, clinically significant MAO-A inhibition does occur; the premise that this patient's crisis occurred with intact MAO-A activity is pharmacologically false and contradicts the prescribing information.
Option D:
Option D: Option D is incorrect because the selegiline transdermal patch delivers the same molecule as oral selegiline — there is no manufacturing modification that changes the chemical identity of selegiline; the pharmacokinetic difference is route of delivery and systemic bioavailability, not molecular structure.
Option E:
Option E: Option E is incorrect because the dose-dependency of tyramine restriction for the transdermal patch is real and explicitly documented — the 6 mg/24 hr patch carries only a precautionary recommendation while the 9 and 12 mg/24 hr doses require restriction; stating that all transdermal doses equally require restriction misrepresents the dose-dependent pharmacology and the prescribing information.
4. A 41-year-old woman with treatment-resistant depression on phenelzine 45 mg daily presents to neurology clinic with a new complaint of migraine headaches occurring three to four times per month with severe unilateral throbbing pain, photophobia, and nausea lasting 6 to 8 hours. She has no history of coronary artery disease. The neurologist wants to prescribe sumatriptan for acute migraine attacks. Which of the following most accurately characterizes the risk and the appropriate management?
A) Sumatriptan can be safely co-prescribed with phenelzine because triptans act at 5-HT1B/1D receptors, which are pharmacologically distinct from the 5-HT2A receptors responsible for serotonin syndrome; receptor subtype separation makes the combination safe
B) Sumatriptan is absolutely contraindicated with phenelzine for two independent reasons: phenelzine's MAO-A inhibition impairs sumatriptan's first-pass and systemic metabolism raising triptan plasma levels substantially, and the combination of MAO-induced serotonin accumulation with triptan-mediated serotonergic activity creates unacceptably high risk of serotonin syndrome and cardiovascular events; alternative acute migraine therapies must be used
C) Sumatriptan can be used at half the standard dose because phenelzine's MAO-A inhibition will reduce sumatriptan's clearance by approximately 50%; dose-adjusted sumatriptan achieves therapeutic concentrations without producing the excess exposure that would cause serotonin syndrome
D) The combination is safe because sumatriptan undergoes first-pass metabolism by MAO-A and phenelzine will actually reduce sumatriptan's plasma concentrations by competitive substrate inhibition at the MAO active site, lowering sumatriptan exposure below the threshold needed for serotonin syndrome
E) Sumatriptan is contraindicated with phenelzine only because of the cardiovascular vasoconstriction risk from elevated triptan levels; serotonin syndrome is not a concern because triptans do not activate the postsynaptic 5-HT2A receptors responsible for the neuromuscular features of serotonin syndrome
ANSWER: B
Rationale:
This question asked you to apply the dual mechanism of the absolute sumatriptan-MAOI contraindication to a clinical scenario. The contraindication operates through two independent pharmacological pathways. First, most triptans including sumatriptan are substrates of MAO-A; when MAO-A is irreversibly inhibited by phenelzine, sumatriptan's first-pass and systemic metabolism is substantially impaired, producing markedly elevated triptan plasma concentrations and amplified cardiovascular effects including coronary vasoconstriction through 5-HT1B receptor activation. Second, phenelzine's MAO-A inhibition causes systemic serotonin accumulation; adding triptan-mediated serotonergic activity to an already serotonin-loaded system raises the risk of serotonin syndrome. These two mechanisms are independent — either alone would be clinically concerning, and both together constitute an absolute contraindication. For this patient's acute migraine, appropriate alternatives include NSAIDs, acetaminophen, antiemetics such as metoclopramide, and ergotamine cautiously (though ergotamines also have serotonergic activity requiring evaluation). A discussion with psychiatry about whether phenelzine can eventually be transitioned should also be initiated.
Option A:
Option A: Option A is incorrect because receptor subtype separation does not make the combination safe; the risk is not about which receptor the triptan activates but about two distinct mechanisms: impaired MAO-A-mediated triptan metabolism raising plasma levels, and additive serotonergic stimulation in a patient already accumulating serotonin from MAO inhibition; both risks are real regardless of which 5-HT receptor subtypes are involved.
Option C:
Option C: Option C is incorrect because the contraindication is absolute, not dose-dependent; there is no safe sumatriptan dose during phenelzine therapy because the interaction operates through two pharmacological mechanisms that are not correctable by dose reduction; the triptan-MAOI combination is listed as an absolute contraindication in the prescribing information for all triptans.
Option D:
Option D: Option D is incorrect and represents a pharmacological error; phenelzine does not reduce sumatriptan plasma concentrations through competitive substrate inhibition — it irreversibly inactivates the MAO-A enzyme entirely, which eliminates sumatriptan's metabolism rather than competing with it; MAO-A inhibition raises sumatriptan levels, it does not lower them.
Option E:
Option E: Option E is incorrect because it incompletely characterizes the contraindication; while the cardiovascular risk from elevated triptan levels is real, serotonin syndrome risk is also genuine — phenelzine's MAO-A inhibition causes widespread serotonin accumulation, and adding any serotonergic stimulus on top of this elevated serotonergic tone increases the risk of serotonin toxicity; the contraindication is based on both mechanisms, not the cardiovascular mechanism alone.
5. A 58-year-old woman is receiving highly emetogenic chemotherapy for ovarian cancer and has been managed with ondansetron 8 mg IV every 8 hours for nausea. On day 2 of her third cycle, routine monitoring reveals a QTc of 498 ms (up from her baseline of 432 ms). Her serum potassium is 3.1 mEq/L and magnesium is 1.6 mEq/L. She is not on any other QTc-prolonging medications. Her nausea control has been adequate. Which of the following is the most appropriate management of her antiemetic regimen?
A) Continue ondansetron at the same dose and frequency because the QTc prolongation is mild and the clinical benefit of nausea control outweighs the cardiac risk in oncology patients receiving active chemotherapy
B) Discontinue all 5-HT3 antagonists immediately and switch to a dopamine D2 antagonist antiemetic such as metoclopramide, which has no QTc risk and can provide equivalent nausea control for highly emetogenic regimens
C) Reduce the ondansetron dose to 4 mg IV every 12 hours because the QTc prolongation is dose-dependent and dose reduction to the lowest effective level will normalize the QTc while maintaining antiemetic coverage
D) Correct the electrolyte abnormalities with intravenous potassium and magnesium supplementation, discontinue ondansetron, and switch to palonosetron or granisetron, which carry lower QTc-prolonging potential than ondansetron at standard doses
E) Add prophylactic magnesium supplementation and continue ondansetron unchanged, because the QTc prolongation is driven entirely by the hypomagnesemia and will resolve with magnesium replacement without any need to change the antiemetic agent
ANSWER: D
Rationale:
This question asked you to manage ondansetron-associated QTc prolongation in a patient with coexisting electrolyte abnormalities. Ondansetron prolongs QTc through dose-dependent hERG potassium channel blockade, reducing the cardiac repolarizing current IKr. QTc prolongation is amplified by hypokalemia (which reduces the driving force for repolarization) and hypomagnesemia (which destabilizes cardiac membrane potential). This patient has all three compounding factors: ondansetron, hypokalemia, and hypomagnesemia. The correct management addresses all contributors: correct the electrolytes with IV potassium and magnesium, discontinue ondansetron as the drug primarily responsible for the additional QTc prolongation, and substitute a 5-HT3 antagonist with lower QTc risk. Both palonosetron and granisetron have lower QTc-prolonging potential than ondansetron at standard clinical doses, providing equivalent antiemetic mechanism while reducing cardiac risk. Maintaining antiemetic coverage is essential in oncology patients receiving highly emetogenic chemotherapy.
Option A:
Option A: Option A is incorrect because a QTc of 498 ms is significantly prolonged and represents a meaningful risk for torsades de pointes, particularly in the context of ondansetron use plus hypokalemia plus hypomagnesemia; a QTc approaching or exceeding 500 ms generally warrants medication change rather than continuation, and the argument that any prolongation is acceptable in oncology patients is pharmacologically unsound.
Option B:
Option B: Option B is incorrect because discontinuing all 5-HT3 antagonists is unnecessary and suboptimal when lower-risk agents within the same class are available; metoclopramide provides dopaminergic antiemetic activity that is less effective than 5-HT3 antagonism for chemotherapy-induced nausea from highly emetogenic regimens; switching to an alternative 5-HT3 antagonist preserves superior antiemetic mechanism while reducing QTc risk.
Option C:
Option C: Option C is incorrect because reducing ondansetron dose alone is inadequate management when the QTc is already 498 ms with coexisting electrolyte abnormalities; dose reduction does not eliminate the QTc risk at lower doses in the presence of hypokalemia and hypomagnesemia, and switching to a lower-risk agent is more appropriate than continuing the same drug at a lower dose.
Option E:
Option E: Option E is incorrect because while hypomagnesemia does contribute to QTc prolongation and should be corrected, the ondansetron-mediated hERG channel blockade is a direct pharmacological effect that is not eliminated by magnesium supplementation alone; magnesium correction reduces QTc risk but does not negate the need to address the drug causing direct potassium channel blockade.
6. A 48-year-old woman with generalized anxiety disorder has been taking lorazepam 1 mg three times daily for the past 4 years. Her primary care physician wants to transition her to buspirone for long-term anxiety management and plans to start buspirone 10 mg twice daily on the same day that lorazepam is stopped. Three days after the switch, the patient calls reporting severe anxiety, insomnia, tremor, and sweating. Later that day she has a witnessed generalized tonic-clonic seizure. Which of the following most accurately explains this outcome and what should have been done differently?
A) The seizure was caused by buspirone's partial agonism at dopamine D2 receptors, which lowered the seizure threshold through a dopaminergic mechanism; the transition should have been made with a lower starting dose of buspirone over 6 to 8 weeks
B) The seizure resulted from a pharmacodynamic interaction between buspirone and residual lorazepam binding at GABA-A receptors; the two drugs should never be co-administered even briefly during a transition period
C) The abrupt discontinuation of lorazepam after 4 years of daily use caused benzodiazepine withdrawal syndrome, which in severe cases includes seizures; buspirone has no GABA-A receptor activity and cannot suppress benzodiazepine withdrawal — lorazepam should have been tapered gradually over weeks to months while buspirone was introduced concurrently
D) The seizure was a manifestation of serotonin syndrome caused by buspirone's 5-HT1A agonism combined with serotonin accumulation from abruptly discontinued lorazepam, which normally suppresses serotonin release through GABA-A-mediated inhibition
E) Buspirone paradoxically lowers the seizure threshold in patients with prior benzodiazepine exposure by upregulating NMDA receptors during the transition period; a 4-week drug-free washout between stopping lorazepam and starting buspirone is required to prevent this interaction
ANSWER: C
Rationale:
This question asked you to identify the cause of post-transition seizure as benzodiazepine withdrawal rather than any buspirone-specific toxicity. After 4 years of daily lorazepam, the GABA-A receptor population undergoes adaptive downregulation and desensitization in response to chronic positive allosteric modulation — a pharmacodynamic tolerance mechanism. Abruptly removing lorazepam leaves these downregulated GABA-A receptors unable to maintain normal inhibitory tone, producing CNS hyperexcitability that manifests as anxiety, insomnia, tremor, diaphoresis, and in severe cases, generalized seizures. Buspirone has absolutely no GABA-A receptor activity — it cannot substitute for lorazepam at the receptor level, provide cross-tolerance, or suppress benzodiazepine withdrawal symptoms. The correct approach is concurrent initiation of buspirone (which will take 2 to 4 weeks to become therapeutically effective) with a slow lorazepam taper over weeks to months, reducing the lorazepam dose gradually enough to allow GABA-A receptor re-upregulation and avoiding withdrawal.
Option A:
Option A: Option A is incorrect because buspirone does not lower seizure threshold through D2 partial agonism; the seizure in this case was a benzodiazepine withdrawal seizure, which is entirely attributable to abrupt lorazepam discontinuation; buspirone's D2 partial agonism is associated with anxiolytic and calming effects, not proconvulsant activity.
Option B:
Option B: Option B is incorrect because buspirone and lorazepam do not have a pharmacodynamic interaction at GABA-A receptors; buspirone has no activity at GABA-A receptors and cannot produce a receptor-level interaction with a benzodiazepine; the premise of this option is pharmacologically impossible.
Option D:
Option D: Option D is incorrect because the mechanism described is pharmacologically false; lorazepam does not suppress serotonin release in a way that, when abruptly removed, would cause serotonin accumulation; benzodiazepine withdrawal is a GABA-A receptor re-normalization process, not a serotonergic rebound; buspirone's 5-HT1A agonism does not cause serotonin syndrome in the absence of other serotonergic agents at clinically relevant doses.
Option E:
Option E: Option E is incorrect because buspirone does not upregulate NMDA receptors or lower seizure threshold in patients with prior benzodiazepine exposure; there is no pharmacological basis for a 4-week drug-free washout between stopping a benzodiazepine and starting buspirone; such a washout would leave the patient without any anxiolytic coverage and at high risk of ongoing withdrawal symptoms.
7. A 52-year-old man with major depressive disorder is well-controlled on vortioxetine 20 mg daily. He presents requesting help with smoking cessation and his physician plans to start bupropion sustained-release 150 mg daily for this purpose. The physician is aware that bupropion also has antidepressant properties and considers whether the combination may even improve his depression. Before prescribing, she checks for drug interactions. Which of the following best describes the pharmacokinetic interaction and the appropriate dose adjustment?
A) Bupropion is a potent CYP2D6 inhibitor; because vortioxetine is primarily metabolized by CYP2D6, co-administration substantially reduces vortioxetine clearance and increases its plasma exposure approximately 2-fold; the vortioxetine dose should be reduced to a maximum of 10 mg daily while the patient remains on bupropion
B) Bupropion induces CYP3A4, which is a secondary metabolic route for vortioxetine; this induction modestly reduces vortioxetine levels by approximately 15 to 20%; no dose adjustment is required as the magnitude is clinically insignificant
C) Vortioxetine inhibits CYP2B6, which is the primary metabolic route for bupropion's conversion to hydroxybupropion; co-administration raises bupropion plasma levels and increases seizure risk; the bupropion dose should be reduced to 100 mg daily
D) Both drugs are serotonergic agents and co-administration is absolutely contraindicated regardless of dose because the combination produces serotonin syndrome risk equivalent to the MAOI-SSRI combination
E) There is no clinically relevant pharmacokinetic interaction between bupropion and vortioxetine; the combination can be prescribed at standard doses for both agents without any pharmacokinetic adjustment
ANSWER: A
Rationale:
This question asked you to identify and act on the CYP2D6-mediated pharmacokinetic interaction between bupropion and vortioxetine. Bupropion is one of the most potent CYP2D6 inhibitors in clinical use — ranked alongside fluoxetine and paroxetine in terms of inhibitory potency. Vortioxetine is metabolized primarily by CYP2D6, with secondary contributions from CYP3A4/5, CYP2C19, and other enzymes. When bupropion inhibits CYP2D6, vortioxetine's primary clearance pathway is substantially impaired, resulting in approximately 2-fold higher vortioxetine plasma concentrations. The vortioxetine prescribing information explicitly addresses this: when a potent CYP2D6 inhibitor such as bupropion is co-administered, the maximum vortioxetine dose should be reduced to 10 mg daily. For this patient currently on 20 mg, the prescriber should reduce vortioxetine to 10 mg at the time bupropion is initiated. The bupropion dose itself does not require adjustment for this interaction.
Option B: Option B has the pharmacokinetic direction and enzyme identification incorrect; bupropion does not induce CYP3A4 — it inhibits CYP2D6; the interaction with vortioxetine is clinically significant and requires dose adjustment, not dismissal as a minor effect.
Option C:
Option C: Option C incorrectly reverses the direction of the pharmacokinetic interaction; vortioxetine is a CYP2D6 substrate, not a CYP2D6 or CYP2B6 inhibitor; vortioxetine does not meaningfully inhibit CYP2B6, does not impair bupropion's conversion to hydroxybupropion, and does not raise bupropion plasma levels; no bupropion dose reduction is required for this combination.
Option D:
Option D: Option D is incorrect because the bupropion-vortioxetine combination is not absolutely contraindicated; bupropion is not a serotonergic agent in the same way as MAOIs or SSRIs and does not produce MAOI-level serotonin syndrome risk; the relevant concern is the pharmacokinetic CYP2D6 interaction, which is manageable with dose adjustment, not an absolute pharmacodynamic contraindication.
Option E:
Option E: Option E is incorrect and represents a dangerous omission; the bupropion-vortioxetine CYP2D6 interaction is well characterized and explicitly addressed in vortioxetine prescribing information; prescribing this combination at standard doses without reducing vortioxetine would expose the patient to approximately double the intended vortioxetine plasma concentration.
8. A 33-year-old woman presents to neurology clinic reporting episodic severe headaches occurring 3 to 4 times per year, each preceded by a 20 to 30-minute aura during which she develops unilateral arm and leg weakness on the side contralateral to her headache, followed by complete resolution of the motor deficit as the headache begins. She has no history of coronary artery disease, hypertension, or stroke. Her cardiovascular examination is normal. A prior neurologist prescribed rizatriptan for acute attacks. Which of the following represents the most important safety concern with this prescription?
A) Rizatriptan should not be used in women of childbearing age because 5-HT1B receptor activation is teratogenic in the first trimester, and this patient is of reproductive age without documented contraception
B) Rizatriptan is contraindicated in patients under 40 years of age without a formal cardiology clearance because the cardiovascular risk from 5-HT1B-mediated coronary vasoconstriction cannot be adequately assessed in young patients without stress testing
C) Rizatriptan at standard doses exceeds the maximum safe triptan exposure for patients with aura-associated migraine, and the dose should be reduced to 5 mg regardless of the migraine subtype
D) Rizatriptan carries a risk of medication overuse headache at 3 to 4 attacks per year; this frequency does not warrant acute treatment and the patient should instead be started on preventive therapy with topiramate
E) Rizatriptan is contraindicated in this patient because her clinical presentation — migraine with unilateral motor weakness preceding the headache that resolves completely — is consistent with hemiplegic migraine, a subtype in which triptan-induced vasoconstriction in regions of already-compromised perfusion carries a risk of extending the neurological deficit or precipitating ischemic injury
ANSWER: E
Rationale:
This question asked you to recognize hemiplegic migraine as a triptan contraindication based on clinical presentation. The defining feature of hemiplegic migraine is a fully reversible motor aura — unilateral weakness or paralysis — that precedes or accompanies the headache. This is distinct from typical migraine aura, which consists of visual, sensory, or speech disturbance without motor weakness. Hemiplegic migraine involves transient neurological dysfunction in specific vascular territories, with evolving perfusion changes in those regions during attacks. Triptan-induced 5-HT1B-mediated vasoconstriction applied to vessels already in a compromised perfusion state during hemiplegic aura carries the risk of worsening or extending the ischemic component of the neurological deficit, or potentially causing lasting injury. Triptans are therefore formally contraindicated in hemiplegic migraine and basilar-type migraine (migraine with brainstem aura). Alternative acute treatments for hemiplegic migraine include NSAIDs, acetaminophen, verapamil, and in some cases intranasal ketamine — none of which carry the vasoconstriction risk.
Option A:
Option A: Option A is incorrect because rizatriptan is not contraindicated in women of childbearing age on the basis of teratogenicity; while triptans are generally used with caution in pregnancy and the prescribing information advises against use in pregnancy primarily due to limited safety data, teratogenicity via 5-HT1B receptor activation is not an established clinical contraindication in non-pregnant women of reproductive age.
Option B:
Option B: Option B is incorrect because triptans are not categorically contraindicated in patients under 40 without cardiology clearance; cardiovascular risk assessment before triptan prescription focuses on established cardiovascular disease, uncontrolled hypertension, and specific high-risk conditions — not on age alone as a criterion requiring stress testing.
Option C:
Option C: Option C is incorrect because rizatriptan dose reduction to 5 mg is not required for all patients with aura-associated migraine; 5 mg is an available dose of rizatriptan but is not mandated for migraine with aura as a safety requirement; the contraindication in this patient is based on the hemiplegic subtype, not simply on the presence of aura.
Option D:
Option D: Option D is incorrect because 3 to 4 attacks per year does not constitute medication overuse (which requires triptan use on 10 or more days per month for at least 3 months); at this attack frequency, acute treatment is entirely appropriate; the primary safety concern is the nature of the migraine subtype, not treatment frequency.
9. A 39-year-old woman with depression is brought to the emergency department by ambulance after being found unresponsive at home. Her partner reports she had been on phenelzine and had taken an unknown quantity of dextromethorphan-containing cough syrup several hours earlier. On examination her temperature is 41.8 degrees Celsius, heart rate 138, blood pressure 162/98, and she has severe generalized muscle rigidity with inducible clonus. Her serum creatine kinase is 22,400 U/L and she is anuric. She cannot swallow. All serotonergic agents have been identified and discontinued. Which of the following best represents the correct immediate treatment approach?
A) Administer cyproheptadine 12 mg orally as loading dose, place the patient in a cool room, and start intravenous fluids for rhabdomyolysis; reserve benzodiazepines only if agitation develops
B) Administer intravenous benzodiazepines immediately for the rigidity and agitation, initiate aggressive active external cooling for the hyperthermia, ensure intravenous fluid resuscitation for rhabdomyolysis-related acute kidney injury, and administer cyproheptadine 12 mg via nasogastric tube given that the patient cannot swallow
C) Administer intravenous dantrolene immediately to block the ryanodine receptor-mediated muscle rigidity, followed by active cooling and intravenous fluids; benzodiazepines and cyproheptadine are unnecessary once the underlying calcium dysregulation is reversed
D) Intubate and initiate neuromuscular blockade with vecuronium to eliminate the muscle rigidity and heat production; avoid benzodiazepines because they lower the seizure threshold in patients with hyperthermia and may worsen CNS toxicity
E) Administer intravenous haloperidol to block dopamine D2 receptors in the hypothalamus, resetting the thermoregulatory set-point; add oral cyproheptadine once the fever begins to respond and the patient can swallow
ANSWER: B
Rationale:
This question presented a life-threatening severe serotonin syndrome requiring coordinated multi-modal management. Several features define this as severe: temperature of 41.8 degrees Celsius, severe muscle rigidity, markedly elevated CK of 22,400 U/L indicating rhabdomyolysis, and anuria reflecting established acute kidney injury. Three simultaneous priorities must be addressed. First, intravenous benzodiazepines are the first-line pharmacological intervention — GABA-A potentiation reduces neuronal excitability, decreases the rigidity and muscular hyperactivity that are generating the extreme hyperthermia, and provides sedation; reducing muscle activity is the most impactful intervention for temperature control. Second, aggressive active external cooling — ice packs, cooling blankets, cold IV fluids — must accompany the benzodiazepines since the hyperthermia is mechanically generated and will not respond to antipyretics. Third, cyproheptadine as a 5-HT2A antagonist addresses the receptor-level mechanism; because the patient cannot swallow, it must be administered via nasogastric tube (it is not available parenterally). Intravenous fluid resuscitation protects against further renal injury from myoglobinuria.
Option A:
Option A: Option A is incorrect because this patient is unable to swallow and cannot take oral cyproheptadine; more critically, cyproheptadine alone without immediate benzodiazepine-mediated muscle relaxation and active cooling is grossly inadequate for a patient with temperature of 41.8 degrees Celsius and rigidity generating ongoing heat; cyproheptadine's adjunctive mechanism-targeted benefit does not replace the need for immediate neuromuscular sedation.
Option C:
Option C: Option C is incorrect because dantrolene is not a standard treatment for serotonin syndrome; the hyperthermia in serotonin syndrome is generated by sustained muscle contraction driven by excess 5-HT receptor activation, not by dysregulated ryanodine receptor-mediated calcium release as in malignant hyperthermia; dantrolene targets the ryanodine receptor pathway, which is not the mechanism in this case.
Option D:
Option D: Option D is incorrect because neuromuscular blockade with vecuronium would eliminate the peripheral manifestations of rigidity and heat production and is a measure of last resort in the most extreme cases unresponsive to benzodiazepines — but avoiding benzodiazepines in favor of neuromuscular blockade as the first step is not the correct approach; benzodiazepines should be given first and urgently, and the claim that they lower seizure threshold in hyperthermia is incorrect — benzodiazepines are anticonvulsant and are protective against seizures.
Option E:
Option E: Option E is incorrect because haloperidol does not treat serotonin syndrome; dopamine D2 blockade is not mechanistically relevant to excess 5-HT receptor activation, and haloperidol does not reset the thermoregulatory set-point in serotonin syndrome; waiting for the fever to respond before giving cyproheptadine orally is also inappropriate when the patient cannot swallow and requires nasogastric administration urgently.
10. A 46-year-old woman with severe treatment-resistant depression has failed adequate trials of sertraline, escitalopram, venlafaxine, and mirtazapine over the past 3 years. Her psychiatrist recommends a trial of phenelzine. She is currently taking fluoxetine 40 mg daily, her most recent antidepressant, which she has been on for 8 months. The psychiatrist plans to stop fluoxetine and start phenelzine after a 14-day washout, reasoning that 2 weeks is sufficient for any SSRI to clear. Which of the following identifies the error in this plan and states the correct washout period?
A) The plan is correct; 14 days is the standard washout period for all SSRIs before starting an irreversible MAOI, and fluoxetine is not an exception because its half-life, while longer than paroxetine, is still within the range cleared by 14 days
B) The error is that no washout is necessary; fluoxetine and phenelzine can be started simultaneously because phenelzine's MAO inhibition only becomes pharmacologically significant after 3 to 4 weeks of administration, during which time fluoxetine will have cleared
C) The error is that a 3-week washout is required for fluoxetine specifically because its half-life of approximately 3 weeks places it just outside the standard 14-day clearance window for most SSRIs
D) The error is that fluoxetine requires a 5-week washout before starting phenelzine — not 14 days — because fluoxetine is metabolized to norfluoxetine, an active metabolite with a half-life of approximately 1 to 2 weeks that continues to occupy SERT and maintain clinically significant serotonin reuptake inhibition for weeks after the parent drug has cleared; starting phenelzine at 14 days post-fluoxetine leaves substantial norfluoxetine-mediated SERT blockade in place
E) The error is that the washout period depends on the patient's CYP2D6 genotype; in CYP2D6 poor metabolizers, fluoxetine accumulates to higher levels and a 6 to 8-week washout is required, while in rapid metabolizers 7 days is sufficient; the psychiatrist should order pharmacogenomic testing before calculating the washout period
ANSWER: D
Rationale:
This question asked you to identify a clinically dangerous error in MAOI transition planning based on fluoxetine's unique pharmacokinetic profile. The standard washout before starting an irreversible MAOI after most SSRIs or SNRIs is 14 days — sufficient for the SSRI to clear and for its SERT-blocking effect to dissipate. Fluoxetine is the exception because it is metabolized to norfluoxetine, an active metabolite with its own potent SERT inhibitor activity and a half-life of approximately 1 to 2 weeks. After stopping fluoxetine, norfluoxetine continues to maintain clinically significant SERT occupancy for weeks. At 14 days post-fluoxetine, norfluoxetine plasma levels are still substantial and SERT blockade is still present. Combining phenelzine's MAO-A inhibition with ongoing norfluoxetine-mediated SERT blockade creates the same high-risk pharmacodynamic situation as directly combining phenelzine with an active SSRI. The standard clinical recommendation is a 5-week washout from the last fluoxetine dose before starting phenelzine. This patient, currently on fluoxetine, would need to stop fluoxetine today and wait 5 full weeks before phenelzine can be initiated safely.
Option A:
Option A: Option A is incorrect because fluoxetine is explicitly an exception to the 14-day washout rule; the standard 14-day period is insufficient because norfluoxetine's approximately 1 to 2-week half-life extends clinically significant SERT blockade beyond the 14-day window; fluoxetine's longer active metabolite half-life is the pharmacokinetic basis for the extended washout requirement.
Option B:
Option B: Option B is incorrect and represents a dangerously wrong clinical recommendation; phenelzine's MAO inhibition is not delayed by 3 to 4 weeks — it begins with the first dose and is effective within days; simultaneously prescribing phenelzine with fluoxetine still on board, or starting phenelzine while norfluoxetine is still present, carries high risk of severe or fatal serotonin syndrome.
Option C:
Option C: Option C is incorrect because it understates the required washout duration; the clinical standard is 5 weeks, not 3 weeks; a 3-week washout is insufficient because norfluoxetine's 1 to 2-week half-life means that after 3 weeks approximately one half-life has elapsed, still leaving substantial norfluoxetine-mediated SERT blockade in place and making phenelzine initiation unsafe at that point.
Option E:
Option E: Option E is incorrect because the 5-week washout recommendation for fluoxetine before an irreversible MAOI is not stratified by CYP2D6 genotype in clinical practice; while CYP2D6 polymorphisms do affect fluoxetine and norfluoxetine metabolism to some degree, the clinical recommendation is a fixed conservative 5-week washout applied uniformly; pharmacogenomic testing is not required or recommended to calculate this specific washout period.
11. A 44-year-old man with major depressive disorder is well-controlled on vortioxetine 10 mg daily. He is diagnosed with pulmonary tuberculosis and his infectious disease physician starts a standard four-drug regimen including rifampin 600 mg daily. Two weeks later the patient reports that his depression has returned — he is experiencing low mood, poor sleep, and loss of motivation that he had not experienced since starting vortioxetine. His plasma vortioxetine level is obtained and found to be markedly reduced compared to his prior measurement. Which of the following best explains this clinical picture and identifies the appropriate pharmacological management?
A) Rifampin inhibits CYP2D6 through a competitive mechanism, reducing vortioxetine's conversion to its active metabolite; increasing the vortioxetine dose will not help because the active metabolite cannot be produced regardless of parent drug dose
B) Rifampin causes clinically significant protein binding displacement of vortioxetine, increasing its volume of distribution and reducing plasma levels; albumin supplementation is required to restore normal vortioxetine plasma protein binding
C) Rifampin is a potent inducer of multiple CYP enzymes including CYP3A4/5 and CYP2C19, which are secondary metabolic routes for vortioxetine; strong induction reduces vortioxetine plasma exposure by approximately 72%, producing subtherapeutic concentrations and recurrence of depressive symptoms; the prescribing information recommends increasing the vortioxetine dose up to a maximum of three times the original dose during rifampin co-administration, meaning this patient's dose could be increased to 30 mg daily
D) Rifampin directly blocks the serotonin transporter through a non-competitive allosteric mechanism, reducing vortioxetine's primary pharmacodynamic target; dose escalation cannot overcome allosteric SERT inhibition and vortioxetine should be switched to an MAOI unaffected by this mechanism
E) Rifampin competes with vortioxetine for 5-HT1A receptor binding, reducing vortioxetine's partial agonist activity at this receptor; because 5-HT1A partial agonism contributes to vortioxetine's multimodal antidepressant effect, competitive receptor displacement reduces efficacy in proportion to rifampin plasma concentration
ANSWER: C
Rationale:
This question asked you to diagnose a CYP enzyme induction-mediated loss of antidepressant efficacy and identify the correct dose adjustment. Rifampin is among the most potent CYP enzyme inducers available, upregulating CYP3A4/5, CYP2C19, CYP2C9, and CYP2B6 among others. Although CYP2D6 is vortioxetine's primary metabolic route, CYP3A4/5 and CYP2C19 provide secondary clearance pathways. When rifampin induces all of these simultaneously, the total increase in vortioxetine clearance reduces plasma exposure by approximately 72% — leaving only approximately 28% of the expected drug levels at the standard dose. The clinical consequence is exactly what this patient is experiencing: subtherapeutic vortioxetine concentrations causing recurrence of depressive symptoms. The vortioxetine prescribing information specifically addresses this: the dose may be increased up to a maximum of three times the original dose when a strong CYP inducer is co-administered. For this patient on 10 mg, the dose can be increased up to 30 mg daily while rifampin therapy continues, and should be reduced back to 10 mg when rifampin is stopped to avoid toxicity from the resumed lower clearance.
Option A: Option A has the rifampin mechanism completely reversed; rifampin is a potent CYP inducer, not a CYP inhibitor; CYP inhibition would raise vortioxetine levels and potentially cause toxicity, not reduce them; furthermore, vortioxetine does not require conversion to an active metabolite — it is pharmacologically active as the parent compound, and all its metabolites are inactive.
Option B:
Option B: Option B is incorrect because rifampin does not cause clinically significant protein binding displacement of vortioxetine; drug interactions mediated by plasma protein binding displacement are rarely clinically meaningful as the displaced free drug is rapidly redistributed and cleared; the established mechanism of the rifampin-vortioxetine interaction is CYP enzyme induction, not protein binding competition.
Option D:
Option D: Option D is incorrect because rifampin has no established pharmacodynamic interaction with the serotonin transporter; rifampin is an antibiotic whose primary mechanism is inhibition of bacterial DNA-dependent RNA polymerase, and it does not interact with human serotonin transporters through any allosteric mechanism; the vortioxetine plasma level reduction is purely pharmacokinetic through CYP induction.
Option E:
Option E: Option E is incorrect because rifampin has no established affinity for 5-HT1A receptors and does not compete with vortioxetine for receptor binding; 5-HT1A receptor binding displacement is not a described pharmacological property of rifampin; the clinical observation of reduced efficacy is entirely explained by the pharmacokinetic reduction in vortioxetine plasma levels through CYP induction.
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