Repeated USMLE Questions Step 1 Review-175- Pharmacology

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Q- A patient with atrial fibrillation is treated with dofetilide. Which electrophysiologic effect explains the antiarrhythmic action of this drug?

A- Decreased phase 0 depolarization

B- Increased refractory period by potassium channel blockade

C- Inhibition of calcium influx in AV node

D- Sodium channel blockade during depolarization

B- Increased refractory period by potassium channel blockade- Dofetilide is a Class III antiarrhythmic that blocks delayed rectifier potassium channels, prolonging repolarization and the action potential duration, which increases the refractory period and prevents reentry arrhythmias.

 

Q- A patient treated with acetazolamide develops metabolic acidosis. What is the mechanism responsible for this effect?

A- Decreased ammonium excretion

B- Increased bicarbonate excretion

C- Increased hydrogen ion secretion

D- Inhibition of aldosterone release

B- Increased bicarbonate excretion- Acetazolamide inhibits carbonic anhydrase in the proximal tubule, preventing bicarbonate reabsorption and causing bicarbonate loss in urine, resulting in metabolic acidosis.

 

Q- A patient taking daptomycin for a resistant infection develops muscle pain and elevated creatine kinase levels. What is the mechanism of action of this drug?

A- Binds D-alanine in bacterial cell walls

B- Blocks bacterial DNA gyrase

C- Creates membrane pores causing depolarization

D- Inhibits bacterial ribosomal protein synthesis

C- Creates membrane pores causing depolarization – Daptomycin inserts into the bacterial cell membrane and forms pores, leading to potassium efflux, membrane depolarization, and rapid bacterial cell death.

 

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Dr Ray Makar
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