100+ USMLE Step 1 pharmacology-style MCQs, aligned with
First Aid for the USMLE Step 1 (2025 Edition) PROCTORED
EXAM TEST BANK 2025 (best answers)
Q1.
A 72-year-old man with a history of atrial fibrillation presents
for routine follow-up. He takes warfarin for stroke prevention.
He recently began taking trimethoprim-sulfamethoxazole for a
urinary tract infection. Two days later, he presents with dark
stools and mild dizziness. His INR is 6.3.
Which of the following best explains the cause of this patient’s
current presentation?
A. Increased warfarin metabolism
B. Vitamin K deficiency
C. Displacement of warfarin from albumin ✅
D. Decreased absorption of warfarin
E. Reduced hepatic synthesis of clotting factors
✅ Correct Answer: C. Displacement of warfarin from albumin
Trimethoprim-sulfamethoxazole displaces warfarin from plasma
proteins, increasing its free (active) concentration. This can lead
to supratherapeutic INR and increased bleeding risk.
❌ Incorrect Answers:
, A. Increased warfarin metabolism – Warfarin is
metabolized by CYP2C9; TMP-SMX inhibits it.
B. Vitamin K deficiency – Not caused by antibiotics this
quickly; INR wouldn't rise this fast.
D. Decreased absorption of warfarin – Would lower INR,
not raise it.
E. Reduced hepatic synthesis of clotting factors –
Warfarin does this, but not the mechanism of TMP-SMX
interaction.
First Aid 2025: Drug Interactions section, p. 258;
Anticoagulants, p. 438.
Tip: Look for drug interactions that displace highly protein-
bound drugs like warfarin or phenytoin.
Q2.
A 23-year-old medical student presents with severe headache,
flushing, and palpitations after eating aged cheese and drinking
red wine. He recently started taking phenelzine for treatment-
resistant depression.
Which of the following best explains his symptoms?
A. Serotonin syndrome
B. Disulfiram-like reaction
C. Tyramine-induced hypertensive crisis ✅
,D. Anticholinergic toxicity
E. Drug-induced lupus
✅ Correct Answer: C. Tyramine-induced hypertensive crisis
Phenelzine is a monoamine oxidase inhibitor (MAOI). It inhibits
breakdown of tyramine, leading to hypertensive crisis when
tyramine-rich foods are ingested.
❌ Incorrect Answers:
A. Serotonin syndrome – Requires serotonergic drugs;
symptoms include clonus, hyperreflexia.
B. Disulfiram-like reaction – Occurs with metronidazole or
certain cephalosporins and alcohol.
D. Anticholinergic toxicity – Dry mouth, urinary retention,
confusion—not hypertensive crisis.
E. Drug-induced lupus – Associated with hydralazine,
procainamide, not MAOIs.
First Aid 2025: Antidepressants table, p. 567.
Tip: Always associate MAOIs with tyramine risk. Aged foods +
MAOI = Step 1 classic.
Q3.
A 34-year-old woman with generalized anxiety disorder begins
treatment with buspirone. After two weeks, she returns
complaining that the medication is not helping her symptoms.
, Which of the following is the most likely explanation?
A. Buspirone has a delayed onset of action ✅
B. The patient has developed tolerance
C. Buspirone requires hepatic activation
D. It is only effective for panic disorder
E. The drug has poor oral bioavailability
✅ Correct Answer: A. Buspirone has a delayed onset of action
Buspirone takes 1–2 weeks for onset of therapeutic effect. It is
not effective for acute anxiety or panic attacks.
❌ Incorrect Answers:
B. Developed tolerance – Tolerance is not typical with
buspirone.
C. Requires hepatic activation – No prodrug metabolism
needed.
D. Only effective for panic disorder – It is used for GAD,
not panic disorder.
E. Poor bioavailability – Not the reason for delayed
efficacy.
First Aid 2025: Anxiolytics section, p. 567.
Tip: Remember the slow onset of buspirone to differentiate it
from benzodiazepines.
Q4.
First Aid for the USMLE Step 1 (2025 Edition) PROCTORED
EXAM TEST BANK 2025 (best answers)
Q1.
A 72-year-old man with a history of atrial fibrillation presents
for routine follow-up. He takes warfarin for stroke prevention.
He recently began taking trimethoprim-sulfamethoxazole for a
urinary tract infection. Two days later, he presents with dark
stools and mild dizziness. His INR is 6.3.
Which of the following best explains the cause of this patient’s
current presentation?
A. Increased warfarin metabolism
B. Vitamin K deficiency
C. Displacement of warfarin from albumin ✅
D. Decreased absorption of warfarin
E. Reduced hepatic synthesis of clotting factors
✅ Correct Answer: C. Displacement of warfarin from albumin
Trimethoprim-sulfamethoxazole displaces warfarin from plasma
proteins, increasing its free (active) concentration. This can lead
to supratherapeutic INR and increased bleeding risk.
❌ Incorrect Answers:
, A. Increased warfarin metabolism – Warfarin is
metabolized by CYP2C9; TMP-SMX inhibits it.
B. Vitamin K deficiency – Not caused by antibiotics this
quickly; INR wouldn't rise this fast.
D. Decreased absorption of warfarin – Would lower INR,
not raise it.
E. Reduced hepatic synthesis of clotting factors –
Warfarin does this, but not the mechanism of TMP-SMX
interaction.
First Aid 2025: Drug Interactions section, p. 258;
Anticoagulants, p. 438.
Tip: Look for drug interactions that displace highly protein-
bound drugs like warfarin or phenytoin.
Q2.
A 23-year-old medical student presents with severe headache,
flushing, and palpitations after eating aged cheese and drinking
red wine. He recently started taking phenelzine for treatment-
resistant depression.
Which of the following best explains his symptoms?
A. Serotonin syndrome
B. Disulfiram-like reaction
C. Tyramine-induced hypertensive crisis ✅
,D. Anticholinergic toxicity
E. Drug-induced lupus
✅ Correct Answer: C. Tyramine-induced hypertensive crisis
Phenelzine is a monoamine oxidase inhibitor (MAOI). It inhibits
breakdown of tyramine, leading to hypertensive crisis when
tyramine-rich foods are ingested.
❌ Incorrect Answers:
A. Serotonin syndrome – Requires serotonergic drugs;
symptoms include clonus, hyperreflexia.
B. Disulfiram-like reaction – Occurs with metronidazole or
certain cephalosporins and alcohol.
D. Anticholinergic toxicity – Dry mouth, urinary retention,
confusion—not hypertensive crisis.
E. Drug-induced lupus – Associated with hydralazine,
procainamide, not MAOIs.
First Aid 2025: Antidepressants table, p. 567.
Tip: Always associate MAOIs with tyramine risk. Aged foods +
MAOI = Step 1 classic.
Q3.
A 34-year-old woman with generalized anxiety disorder begins
treatment with buspirone. After two weeks, she returns
complaining that the medication is not helping her symptoms.
, Which of the following is the most likely explanation?
A. Buspirone has a delayed onset of action ✅
B. The patient has developed tolerance
C. Buspirone requires hepatic activation
D. It is only effective for panic disorder
E. The drug has poor oral bioavailability
✅ Correct Answer: A. Buspirone has a delayed onset of action
Buspirone takes 1–2 weeks for onset of therapeutic effect. It is
not effective for acute anxiety or panic attacks.
❌ Incorrect Answers:
B. Developed tolerance – Tolerance is not typical with
buspirone.
C. Requires hepatic activation – No prodrug metabolism
needed.
D. Only effective for panic disorder – It is used for GAD,
not panic disorder.
E. Poor bioavailability – Not the reason for delayed
efficacy.
First Aid 2025: Anxiolytics section, p. 567.
Tip: Remember the slow onset of buspirone to differentiate it
from benzodiazepines.
Q4.
