USMLE Step 1 Practice Exam: Pharmacology Questions
Correct Answers in Bold and Detailed Rationales
Prepared for: USMLE Step 1 Review | Focus: Pharmacology High-Yield Topics
1. A 45-year-old man with hypertension is started on a drug that decreases
peripheral vascular resistance without affecting cardiac output or renal blood
flow. Which drug is most likely prescribed?
A) Propranolol
B) Hydralazine
C) Furosemide
D) Lisinopril
E) Verapamil
Answer: B) Hydralazine
Rationale: Hydralazine is a direct arteriolar vasodilator that decreases peripheral
resistance, reducing blood pressure without significant effect on cardiac output or
renal blood flow. Propranolol is a beta-blocker; furosemide is a diuretic; lisinopril
is an ACE inhibitor; verapamil is a calcium channel blocker with negative inotropic
effects.
2. Which of the following drugs is an irreversible inhibitor of cyclooxygenase
(COX) enzymes?
,A) Ibuprofen
B) Acetaminophen
C) Aspirin
D) Celecoxib
E) Naproxen
Answer: C) Aspirin
Rationale: Aspirin irreversibly acetylates COX-1 and COX-2 enzymes, inhibiting
thromboxane A2 production in platelets, leading to antiplatelet effects. Other
NSAIDs like ibuprofen reversibly inhibit COX enzymes.
3. A patient develops serotonin syndrome after starting a new medication.
Which class of drugs is most commonly associated with this syndrome?
A) Beta-blockers
B) Selective serotonin reuptake inhibitors (SSRIs)
C) Calcium channel blockers
D) Angiotensin receptor blockers
E) Benzodiazepines
Answer: B) Selective serotonin reuptake inhibitors (SSRIs)
Rationale: SSRIs increase serotonin levels and are commonly implicated in
serotonin syndrome, especially when combined with other serotonergic drugs.
Symptoms include agitation, hyperreflexia, and autonomic instability.
4. Which drug is used to reverse benzodiazepine overdose?
, A) Flumazenil
B) Naloxone
C) Physostigmine
D) Atropine
E) Protamine sulfate
Answer: A) Flumazenil
Rationale: Flumazenil is a competitive antagonist at the benzodiazepine binding
site on the GABA-A receptor and is used to reverse benzodiazepine overdose.
Naloxone is for opioid overdose.
5. A patient is treated with a drug that inhibits the bacterial enzyme
dihydrofolate reductase. Which drug is it?
A) Ciprofloxacin
B) Sulfamethoxazole
C) Trimethoprim
D) Penicillin
E) Tetracycline
Answer: C) Trimethoprim
Rationale: Trimethoprim inhibits bacterial dihydrofolate reductase, blocking
tetrahydrofolate synthesis, critical for DNA synthesis. Sulfamethoxazole inhibits
an earlier step (dihydropteroate synthase).
Correct Answers in Bold and Detailed Rationales
Prepared for: USMLE Step 1 Review | Focus: Pharmacology High-Yield Topics
1. A 45-year-old man with hypertension is started on a drug that decreases
peripheral vascular resistance without affecting cardiac output or renal blood
flow. Which drug is most likely prescribed?
A) Propranolol
B) Hydralazine
C) Furosemide
D) Lisinopril
E) Verapamil
Answer: B) Hydralazine
Rationale: Hydralazine is a direct arteriolar vasodilator that decreases peripheral
resistance, reducing blood pressure without significant effect on cardiac output or
renal blood flow. Propranolol is a beta-blocker; furosemide is a diuretic; lisinopril
is an ACE inhibitor; verapamil is a calcium channel blocker with negative inotropic
effects.
2. Which of the following drugs is an irreversible inhibitor of cyclooxygenase
(COX) enzymes?
,A) Ibuprofen
B) Acetaminophen
C) Aspirin
D) Celecoxib
E) Naproxen
Answer: C) Aspirin
Rationale: Aspirin irreversibly acetylates COX-1 and COX-2 enzymes, inhibiting
thromboxane A2 production in platelets, leading to antiplatelet effects. Other
NSAIDs like ibuprofen reversibly inhibit COX enzymes.
3. A patient develops serotonin syndrome after starting a new medication.
Which class of drugs is most commonly associated with this syndrome?
A) Beta-blockers
B) Selective serotonin reuptake inhibitors (SSRIs)
C) Calcium channel blockers
D) Angiotensin receptor blockers
E) Benzodiazepines
Answer: B) Selective serotonin reuptake inhibitors (SSRIs)
Rationale: SSRIs increase serotonin levels and are commonly implicated in
serotonin syndrome, especially when combined with other serotonergic drugs.
Symptoms include agitation, hyperreflexia, and autonomic instability.
4. Which drug is used to reverse benzodiazepine overdose?
, A) Flumazenil
B) Naloxone
C) Physostigmine
D) Atropine
E) Protamine sulfate
Answer: A) Flumazenil
Rationale: Flumazenil is a competitive antagonist at the benzodiazepine binding
site on the GABA-A receptor and is used to reverse benzodiazepine overdose.
Naloxone is for opioid overdose.
5. A patient is treated with a drug that inhibits the bacterial enzyme
dihydrofolate reductase. Which drug is it?
A) Ciprofloxacin
B) Sulfamethoxazole
C) Trimethoprim
D) Penicillin
E) Tetracycline
Answer: C) Trimethoprim
Rationale: Trimethoprim inhibits bacterial dihydrofolate reductase, blocking
tetrahydrofolate synthesis, critical for DNA synthesis. Sulfamethoxazole inhibits
an earlier step (dihydropteroate synthase).
