,USMLE Step 1 Pharmacology Revision: 100 MCQs
Each question is presented as a clinical vignette followed by
4–5 answer choices (one correct). Explanations include:
✅ Correct Answer: Rationale
❌ Incorrect Choices: Brief rationale
First Aid 2025 Reference: page or section
USMLE-style Tip
1. A 55-year-old patient presents with a 2-day history of
productive cough, fever, and dyspnea. He has a history of
chronic obstructive pulmonary disease (COPD). Sputum culture
grows Pseudomonas aeruginosa. Which antibiotic’s mechanism
involves blocking bacterial DNA gyrase?
A. Azithromycin
B. Ciprofloxacin
,C. Doxycycline
D. Gentamicin
E. Linezolid
✅ Correct Answer: B. Ciprofloxacin – Fluoroquinolone that
inhibits DNA gyrase (topoisomerase II) and topoisomerase IV
(FA 2025, p. 120).
❌ A. Azithromycin – Macrolide; inhibits 50S ribosomal subunit.
❌ C. Doxycycline – Tetracycline; blocks 30S.
❌ D. Gentamicin – Aminoglycoside; causes misreading at 30S.
❌ E. Linezolid – Oxazolidinone; blocks initiation at 50S.
USMLE-style Tip: Fluoroquinolone names often end in "-
floxacin."
2. A 25-year-old woman with bipolar disorder experiences a
lithium level of 1.8 mEq/L (therapeutic 0.6–1.2). She reports
tremor, nausea, and confusion. Which is the most likely drug
causing decreased lithium clearance?
A. Hydrochlorothiazide
B. Ibuprofen
C. Spironolactone
D. Verapamil
E. All of the above
✅ Correct Answer: E. All of the above – Thiazides, NSAIDs, and
some CCBs reduce renal clearance of lithium (FA 2025, p. 226).
❌ A-D individually – Each alone is correct, but the question
, asks for the most likely cause: multiple agents interact.
USMLE-style Tip: Lithium competes for reabsorption in PCT; any
change in renal handling matters.
3. A 68-year-old man with atrial fibrillation is started on
warfarin. Which lab test best monitors its effect?
A. Activated partial thromboplastin time (aPTT)
B. Bleeding time
C. International normalized ratio (INR)
D. Platelet count
E. Prothrombin time (PT)
✅ Correct Answer: C. INR – Standardized PT for warfarin
monitoring (FA 2025, p. 264).
❌ A. aPTT – Heparin monitoring.
❌ B. Bleeding time – Platelet function.
❌ D. Platelet count – Quantitative platelets.
❌ E. PT – Used but not standardized; INR preferred.
USMLE-style Tip: "PT-INR" is warfarin’s metric.
4. A 7-year-old boy with leukemia receives doxorubicin. Which
protects the heart from free radical damage when co-
administered?
A. Amifostine
B. Dexrazoxane
Each question is presented as a clinical vignette followed by
4–5 answer choices (one correct). Explanations include:
✅ Correct Answer: Rationale
❌ Incorrect Choices: Brief rationale
First Aid 2025 Reference: page or section
USMLE-style Tip
1. A 55-year-old patient presents with a 2-day history of
productive cough, fever, and dyspnea. He has a history of
chronic obstructive pulmonary disease (COPD). Sputum culture
grows Pseudomonas aeruginosa. Which antibiotic’s mechanism
involves blocking bacterial DNA gyrase?
A. Azithromycin
B. Ciprofloxacin
,C. Doxycycline
D. Gentamicin
E. Linezolid
✅ Correct Answer: B. Ciprofloxacin – Fluoroquinolone that
inhibits DNA gyrase (topoisomerase II) and topoisomerase IV
(FA 2025, p. 120).
❌ A. Azithromycin – Macrolide; inhibits 50S ribosomal subunit.
❌ C. Doxycycline – Tetracycline; blocks 30S.
❌ D. Gentamicin – Aminoglycoside; causes misreading at 30S.
❌ E. Linezolid – Oxazolidinone; blocks initiation at 50S.
USMLE-style Tip: Fluoroquinolone names often end in "-
floxacin."
2. A 25-year-old woman with bipolar disorder experiences a
lithium level of 1.8 mEq/L (therapeutic 0.6–1.2). She reports
tremor, nausea, and confusion. Which is the most likely drug
causing decreased lithium clearance?
A. Hydrochlorothiazide
B. Ibuprofen
C. Spironolactone
D. Verapamil
E. All of the above
✅ Correct Answer: E. All of the above – Thiazides, NSAIDs, and
some CCBs reduce renal clearance of lithium (FA 2025, p. 226).
❌ A-D individually – Each alone is correct, but the question
, asks for the most likely cause: multiple agents interact.
USMLE-style Tip: Lithium competes for reabsorption in PCT; any
change in renal handling matters.
3. A 68-year-old man with atrial fibrillation is started on
warfarin. Which lab test best monitors its effect?
A. Activated partial thromboplastin time (aPTT)
B. Bleeding time
C. International normalized ratio (INR)
D. Platelet count
E. Prothrombin time (PT)
✅ Correct Answer: C. INR – Standardized PT for warfarin
monitoring (FA 2025, p. 264).
❌ A. aPTT – Heparin monitoring.
❌ B. Bleeding time – Platelet function.
❌ D. Platelet count – Quantitative platelets.
❌ E. PT – Used but not standardized; INR preferred.
USMLE-style Tip: "PT-INR" is warfarin’s metric.
4. A 7-year-old boy with leukemia receives doxorubicin. Which
protects the heart from free radical damage when co-
administered?
A. Amifostine
B. Dexrazoxane
