11 USMLE Pharmacology Mechanism Questions with Answers and Explanations (Set 5)

These 11 USMLE pharmacology practice questions (Set 5) cover antiarrhythmic drug classes, seizure emergencies, diabetes drugs, prostate drugs, chemotherapy, osteoporosis treatment, drugs that trigger angle-closure glaucoma and drug-induced lupus. Each question includes the correct answer and an explanation.

Written by Dr. Ray Makar, MD, author of the Repeated USMLE Questions eBook series.

Prefer video? Watch daily USMLE case questions on MedFocus by Dr. Ray on YouTube.

How to use this page: read the question, pick your answer, then tap Show Answer and Explanation.

Questions

Question 1. A group of drugs that bind to a receptor but do not produce any pharmacological effect is called which one of the following?

A- Agonist
B- Antagonist
C- Partial agonist

B- Antagonist-Antagonists work by blocking or inhibiting the action of agonists, which are drugs or endogenous substances that bind to receptors and produce a pharmacological response. By binding to receptors without activating them, antagonists prevent agonists from exerting their effects, effectively blocking or reducing the response mediated by the receptor. In contrast, agonists and partial agonists whether they are drugs or endogenous substances bind to receptors to activate them, producing a pharmacological effect.
The correct answer is B

 

Question 2. Which one of the following drugs is a sodium channel blocker (Class I)?

A- Amiodarone
B- Carvedilol
C- Procainamide
D- Verapamil

C- Procainamide- Class I antiarrhythmics block sodium channels: IA (quinidine, procainamide, disopyramide), IB (lidocaine, mexiletine) and IC (flecainide, propafenone).
The correct answer is C

 

Question 3. Which one of the following drugs is a beta blocker (Class II)?

A- Amiodarone
B- Carvedilol
C- Procainamide
D- Verapamil

B- Carvedilol- Class II antiarrhythmics are beta-blockers such as metoprolol, esmolol and carvedilol.
The correct answer is B

 

Question 4. Which one of the following drugs is a potassium channel blocker (Class III)?

A- Amiodarone
B- Carvedilol
C- Procainamide
D- Verapamil

A- Amiodarone- Class III antiarrhythmics block potassium channels and prolong repolarization: amiodarone, sotalol, dofetilide, ibutilide.
The correct answer is A

 

Question 5. A patient presents to the ER with multiple episodes of tonic-clonic seizures for the past hour. The patient does not recover between these episodes. Which of the following is the treatment of choice in this condition?

A- Fosphenytoin
B- Gabapentin
C- Lorazepam
D- Valproic acid

C- Lorazepam- This is a case of status epilepticus. The treatment of choice is benzodiazepines such as lorazepam or diazepam. Fosphenytoin is the second in order. Gabapentin is for partial seizures, and valproic acid is used as a regular treatment for tonic-clonic seizures.
The correct answer is C

 

Question 6. A 56-year-old man with a history of type 2 diabetes presents to his physician for a follow up. He complains of recurrent hypoglycemic reactions to his medications. Which of these medications is most likely responsible for this patient’s complaint?

A- Acarbose
B- Glyburide
C- Metformin
D- Rosiglitazone

B- Glyburide- The only medication on the list that its mechanism is to release insulin from the pancreas is glyburide. Release of insulin in type 2 diabetes causes hypoglycemic reactions. Other drugs lower blood glucose through other mechanisms i.e., euglycemic as metformin or preventing postprandial hypoglycemia as acarbose.
The correct answer is B

 

Question 7. A 66-year-old man complains of difficult micturition and dribbling at the end of urination. Laboratory investigations and imaging studies confirm the diagnosis of benign prostatic hyperplasia and exclude prostate cancer. Which of these drugs is the most appropriate for this patient?

A- Abiraterone
B- Finasteride
C- Flutamide
D- Pergolide
E- Leuprolide

All drugs mentioned above are used in the treatment of cancer prostate except finasteride which is a dihydrotestosterone (DHT) inhibitor which is also known as 5α-Reductase inhibitors. This enzyme is essential for the growth and development of prostate gland.
The correct answer is B

 

Question 8. A 24-year-old man with a history of HIV infection develops pallor and increasing fatigue. Laboratory tests confirm the diagnosis of acute lymphoblastic leukemia. Which one of these chemotherapeutic agents is used for this patient without causing further damage to his immune system?

A- Chlorambucil
B- Cisplatin
C- Ifosfamide
D- Procarbazine
E- Vincristine

All the drugs mentioned in the answer choices are alkylating agents except vincristine which is a mitotic inhibitor. It is not associated with bone marrow depression.
Alkylating agents are associated with bone marrow depression and for this reason they are inappropriate for this patient.
The correct answer is E

 

Question 9. A 64-year-old woman complains of low back pain for 1 week. Her pain and tenderness are localized over the lumbar spine and exaggerated by movement. Her physician prescribes a bisphosphonate. What is the mechanism of action of this drug for this patient?

A- Decrease osteoclast activity
B- Decrease parathormone activity
C- Increase osteoblast activity
D- Increase vitamin D absorption
E- Increase urinary calcium reabsorption

A- Decrease osteoclast activity- This is most likely a case of osteoporosis. Bisphosphonates improve this condition through decreasing osteoclast activity. Bisphosphonates are also the drug of choice in Paget’s disease of bone. Osteoblast activity is regulated by growth factors and parathyroid hormone. Calcium level of the blood is regulated by parathormone and vitamin D in addition to other factors.
The correct answer is A

 

Question 10. A 45-year-old woman is sent to the emergency room from a vision center after examining her eyes to get new glasses. While she was in the waiting room, she developed severe ocular pain in her right eye and she started seeing halos around light. Which of these agents most likely is the reason for this patient’s condition?

A- Acetazolamide
B- Atropine
C- Neomycin
D- Pilocarpine
E- Timolol

Primary closed angle glaucoma is a medical emergency. It occurs quickly due to sudden increase of intraocular pressure. Acute attack may be precipitated by dilation of the pupil after application of atropine eye drops as in this patient. Neomycin is an antibiotic and has no role in glaucoma. Other agents are used in the treatment of glaucoma.
The correct answer is B

 

Question 11. A 62-year-old man presents to the clinic with rashes all over his body and painful joints. Last month, he was diagnosed with arrhythmia. He is taking one medication for it. Laboratory tests reveal anti-histone antibodies. Which of the following drugs is most likely responsible for this condition?

A- Hydralazine
B- Metoprolol
C- Propranolol
D- Sotalol
E- Verapamil

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Hydralazine use is known for causing lupus-like syndrome which is characterized by joint pain, skin rashes, swollen glands and muscle aches with fever. Anti-histone antibodies test is diagnostic.
The correct answer is A

 

High-yield points from this set

  • Class I = sodium channel blockers; II = beta-blockers; III = potassium channel blockers; IV = calcium channel blockers.
  • Status epilepticus: IV lorazepam first, then fosphenytoin or levetiracetam.
  • Sulfonylureas such as glyburide release insulin and cause hypoglycemia.
  • Finasteride (5-alpha reductase inhibitor) shrinks the prostate in BPH.
  • Vincristine causes little bone marrow suppression; its main toxicity is neuropathy.
  • Bisphosphonates reduce osteoclast activity.
  • Atropine and other mydriatics can trigger acute angle-closure glaucoma.
  • Hydralazine causes drug-induced lupus with anti-histone antibodies.
  • An antagonist binds a receptor without producing an effect.

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