USMLE Pharmacology

Question 1

A patient on warfarin develops supratherapeutic INR after starting a new antibiotic. Which mechanism best explains this interaction?

Accepted Answer

Inhibition of CYP2C9 by the antibiotic

Answer

Many antibiotics inhibit CYP2C9, which metabolizes warfarin, leading to decreased warfarin clearance and elevated INR.

Question 2

Which beta-blocker is cardioselective and preferred in a patient with COPD requiring beta-blockade?

Accepted Answer

Metoprolol

Answer

Metoprolol is a beta-1 selective blocker, making it safer in COPD patients by minimizing beta-2 bronchospasm compared to non-selective agents.

Question 3

A patient with type 2 diabetes develops lactic acidosis. Which medication is most likely responsible?

Accepted Answer

Metformin

Answer

Metformin can cause lactic acidosis, particularly in patients with renal insufficiency, hepatic disease, or conditions causing tissue hypoperfusion.

Question 4

Which antiepileptic drug works by blocking voltage-gated sodium channels and is also used for neuropathic pain and bipolar disorder?

Accepted Answer

Carbamazepine

Answer

Carbamazepine blocks voltage-gated sodium channels and is used for partial seizures, trigeminal neuralgia, and bipolar disorder.

Question 5

A patient develops gynecomastia while taking spironolactone. What is the mechanism of this side effect?

Accepted Answer

Antagonism of androgen receptors

Answer

Spironolactone non-selectively antagonizes androgen receptors in addition to mineralocorticoid receptors, causing gynecomastia and sexual dysfunction in males.

USMLE Practice Test

USMLE Practice Test

USMLE Pharmacology