Questions and Answers for Medical Students- Pharmacology- 6

Q- A 72-year-old man taking warfarin has a large GI bleed. His INR is 9. What is the best way to reverse the anticoagulation?

A- IV vitamin K plus prothrombin complex concentrate

B- Protamine sulfate

C- Idarucizumab

D- Andexanet alfa

A- IV vitamin K plus prothrombin complex concentrate (PCC). Warfarin blocks vitamin K epoxide reductase, lowering factors II, VII, IX, and X. PCC replaces these factors quickly, and vitamin K restores their synthesis. Protamine reverses heparin, idarucizumab reverses dabigatran, and andexanet alfa reverses factor Xa inhibitors (rivaroxaban, apixaban).

Q- A 55-year-old woman develops a persistent dry cough 3 weeks after starting lisinopril for hypertension. What is the mechanism of this side effect?

A- Increased bradykinin

B- Decreased angiotensin II

C- Increased aldosterone

D- Histamine release from mast cells

A- Increased bradykinin. ACE also breaks down bradykinin, so ACE inhibitors raise bradykinin levels, causing cough and sometimes angioedema. Switching to an angiotensin receptor blocker such as losartan avoids this. ACE inhibitors are contraindicated in pregnancy.

Q- A 20-year-old woman is brought to the emergency department 4 hours after taking a large number of acetaminophen tablets. What is the antidote?

A- N-acetylcysteine

B- Flumazenil

C- Naloxone

D- Fomepizole

A- N-acetylcysteine. In overdose, acetaminophen is converted to the toxic metabolite NAPQI, which depletes glutathione and damages the liver. N-acetylcysteine replenishes glutathione and works best within 8 hours. Flumazenil reverses benzodiazepines, naloxone reverses opioids, and fomepizole treats methanol and ethylene glycol poisoning.

Q- A patient treated with gentamicin develops hearing loss and a rising creatinine. What is the mechanism of action of this drug?

A- Binds the 30S ribosomal subunit and blocks formation of the initiation complex

B- Inhibits peptidyl transferase on the 50S subunit

C- Inhibits cell wall synthesis

D- Inhibits DNA gyrase

A- Binds the 30S ribosomal subunit. Aminoglycosides block the initiation complex and cause misreading of mRNA. They are bactericidal, need oxygen to enter bacteria (so they do not work against anaerobes), and cause nephrotoxicity and ototoxicity. Chloramphenicol inhibits 50S peptidyl transferase, beta-lactams inhibit cell wall synthesis, and fluoroquinolones inhibit DNA gyrase.

Q- A 60-year-old man taking atorvastatin develops muscle pain and a high creatine kinase after another lipid-lowering drug is added. Which drug most likely caused this interaction?

A- Gemfibrozil

B- Ezetimibe

C- Omega-3 fatty acids

D- Colesevelam

A- Gemfibrozil. Combining a statin with a fibrate, especially gemfibrozil, greatly increases the risk of myopathy and rhabdomyolysis. The risk is also increased by CYP3A4 inhibitors such as macrolides, azole antifungals, and grapefruit juice. Statins inhibit HMG-CoA reductase, the rate-limiting enzyme of cholesterol synthesis.