10 USMLE Pharmacology Mechanism Questions with Answers and Explanations (Set 2)

These 10 USMLE pharmacology practice questions (Set 2) cover mechanisms, adverse effects and pharmacokinetics: NSAIDs, TB drugs, theophylline toxicity, antiepileptics, aminoglycosides, antifungals, gout drugs, half-life calculation, anxiolytics and metformin. 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 32-year-old woman presents with a complaint of severe pain during menstruation. She is prescribed indomethacin. Which of the following is the mechanism of action of this drug to reduce her pain?

A- Interferes with the production of leukotrienes
B- Limits the production of histamine
C- Stimulates the production of prostaglandin E2
D- Inhibits the production of prostaglandin E2
E- Inhibits the production of Phospholipase A2

Indomethacin is a nonsteroidal anti-inflammatory drug (NSAID). Its primary mechanism of action is the inhibition of cyclooxygenase (COX-1 and COX-2) enzymes, which are essential for the synthesis of prostaglandins, including prostaglandin E2 (PGE2). Prostaglandin E2 contributes to uterine contractions and dysmenorrhea. By reducing PGE2 levels, indomethacin alleviates uterine cramping and associated pain.
Leukotrienes are products of the lipoxygenase pathway, not the COX pathway. Indomethacin doesn’t interfere with their production.
Histamine is released from mast cells and is not directly affected by NSAIDs.
Corticosteroids, not NSAIDs, inhibit the production of phospholipase A2.
The correct answer is D

 

Question 2. A 23-year-old man who takes anti-mycobacterial therapy for pulmonary tuberculosis presents to the clinic because of recent visual disturbance and pain with movement of his left eye. On examination, there is tenderness to the pressure of the left eye and a blind spot at the center of vision. Fundus examination reveals pale optic disc. What is the most likely etiology of this patient’s visual symptoms?

A- As a complication of tuberculosis
B- A side effect of isoniazid
C- A side effect of rifampin
D- A side effect of ethambutol
E- A side effect of pyrazinamide

Optic neuritis is a side effect of ethambutol. It causes dimension or loss of vision, pain and tenderness with eye movement. It is very uncommon for pulmonary TB to affect the eye. Isoniazid use can cause numbness, tingling, nausea, vomiting or abnormal liver function tests. Rifampin is known for heartburn, menstrual changes, headache and dizziness. Pyrazinamide also causes upset stomach, nausea and slight pain in bones and muscles.
The correct answer is D

 

Question 3. A 21-year-old medical student with asthma takes theophylline. He discusses its narrow therapeutic index with his physician. If he develops theophylline toxicity with a dangerous tachyarrhythmia, which of these drugs can be used to control the heart rate?

A- Albuterol
B- Esmolol
C- Digoxin
D- Epinephrine
E- Furosemide

Theophylline is a nonselective phosphodiesterase inhibitor (and adenosine receptor blocker). In toxicity it causes nausea, vomiting, tremor, seizures and tachyarrhythmias. A short-acting cardioselective beta-blocker such as esmolol can control the tachycardia, used with caution in asthma. The main treatment of theophylline toxicity is supportive: repeated activated charcoal, benzodiazepines for seizures and hemodialysis for severe cases. Albuterol and epinephrine would worsen the tachycardia.
The correct answer is B

 

Question 4. A 30-year-old man with a history of recurrent generalized tonic-clonic seizures visits his neurologist to refill his prescriptions. He complains of recent diplopia and ataxia. His doctor thinks that these new symptoms are related to one of his medications. Which of these drugs is most likely responsible for these new symptoms?

A- Acetazolamide
B- Carbamazepine
C- Clonazepam
D- Ethosuximide
E- Gabapentin

Out of this list of drugs, only carbamazepine can cause diplopia. Ataxia also is a common side effect of carbamazepine but it occurs with some other medications as well. Side effects of acetazolamide include renal calculi and metabolic acidosis. Clonazepam can cause drowsiness and behavioral abnormalities. Ethosuximide and gabapentin may lead to drowsiness and headache.
The correct answer is B

 

Question 5. A 72-year-old woman presents to her physician complaining of abdominal pain and frequent episodes of burning micturition. After physical examination and laboratory tests, she is diagnosed with urinary tract infection. She is prescribed gentamicin in addition to other medications. What is the most likely complication attributed to this antibiotic?

A- Hepatic toxicity
B- Hearing loss
C- Thrombocytopenia
D- Agranulocytosis

Gentamicin is one of the aminoglycosides. It is used against a lot of organisms mainly gram negative bacteria such as Pseudomonas, Proteus and gram positive Staphylococci. It is not used in Neisseria or legionella infections due to the risk of shock as a result of the release of Lipid A endotoxin found in these organisms. Side effects of aminoglycosides are:
“No Need Of Toxins”….monomeric stands for Nephrotoxic, Neuromuscular blockade, Ototoxic and Teratogen. Aminoglycosides don’t cause hepatic toxicity or any blood abnormality.
The correct answer is B

 

Question 6. A 19-year-old man with a history of immunodeficiency disease develops fever. Prophylactic measures including some medications are initiated. A few days later, the patient develops acute renal failure. Which of these drugs is most likely responsible?

A- Acyclovir
B- Amphotericin B
C- Ampicillin
D- Ciprofloxacin
E- Nystatin

Amphotericin B has been known for causing renal problems through decreasing creatinine clearance. Liposomal preparation of this drug may reduce renal side effects. Acyclovir, ampicillin, ciprofloxacin and nystatin less likely affect renal functions.
The correct answer is B

 

Question 7. A 52-year-old man who is recently diagnosed with gout visits his physician to discuss his treatment plan. One of the treatments that will be taken is allopurinol. Which of these enzymes is targeted by this medication?

A- Hypoxanthine guanine phosphoribosyltransferase
B- Phosphoribosylpyrophosphate synthase
C- Guanase
D- Xanthine oxidase

Allopurinol is used to treat chronic gout due to its ability to decrease the production of uric acid in the body. Allopurinol is known to be an inhibitor of xanthine oxidase. Xanthine oxidase catalyzes the oxidation of hypoxanthine to xanthine and the oxidation of xanthine to uric acid.
The correct answer is D

 

Question 8. Studies are done on normal volunteers for phase 1 clinical trials of a new drug. The volume of distribution and clearance has been measured. The researchers now are calculating the half-life of the drug. Assuming that the volume of distribution is 60 L and the clearance is 3 L/hour, what is the approximate half-life of this drug?

A- 1/2 an hour
B- 6 hours
C- 12 hours
D- 14 hours
E- 18 hours

To calculate the half-life of a drug, we need to memorize this equation:
t(½) = 0.7 x (Vd/CL)
= 7/10 x 60/3
= 14
The correct answer is D

 

Question 9. A 24-year-old woman visits her physician for treatment of anxiety. She requests to change her current medication because it is sedative. Which one of these drugs has the minimum sedative effect?

A- Buspirone
B- Lorazepam
C- Midazolam
D- Promethazine
E- Trazodone

Buspirone is non-benzodiazepine anti-anxiety medication and has the minimum sedation effect compared to benzodiazepines such as lorazepam and midazolam. Promethazine is anti-emetic drug associated with sedation, confusion and disorientation. Trazodone is an anti-depressant and effective in insomnia. It causes sedation, dizziness and drowsiness.
The correct answer is A

 

Question 10. An obese 46-year-old man presents to the clinic with complaints of weakness, fatigue and tingling and numbness of his hands and feet. He rarely exercises and he eats almost daily in fast food restaurants. Laboratory tests show fasting blood glucose of 156 mg/dL. He is advised to improve his lifestyle and follow up in 2 weeks. On the next visit, the level of blood glucose is 164 mg/dL. Which of these drugs improves his condition without affecting insulin secretion?

A- Chlorpropamide
B- Glipizide
C- Glyclopyramide
D- Metformin
E- Tolazamide

The mechanism of action of metformin is minimizing the production of glucose in the liver and increasing the uptake of glucose in the liver.
Sulfonylurea derivatives such as carbetamide, glipizide, glyclopyramide and tolazamide stimulate the secretion of insulin from the pancreas.
The correct answer is D

 

High-yield points from this set

  • NSAIDs inhibit COX-1 and COX-2 and lower prostaglandin E2, relieving dysmenorrhea.
  • Ethambutol causes optic neuritis (central scotoma, red-green color loss).
  • Theophylline toxicity: seizures and arrhythmias; activated charcoal, benzodiazepines, esmolol, dialysis.
  • Carbamazepine toxicity causes diplopia and ataxia.
  • Aminoglycosides such as gentamicin cause ototoxicity and nephrotoxicity.
  • Amphotericin B is nephrotoxic; liposomal forms reduce the risk.
  • Allopurinol inhibits xanthine oxidase.
  • Half-life = 0.7 × Vd / clearance.
  • Buspirone is a non-sedating anxiolytic (5-HT1A partial agonist).
  • Metformin lowers hepatic glucose production without increasing insulin secretion.

Keep practicing

Leave a Comment