MCCQE Antimicrobial Pharmacology 2

Question 1

A patient with a penicillin allergy requires treatment for a serious Staphylococcus aureus infection. Which antibiotic has the highest risk of cross-reactivity with penicillin?

Accepted Answer

Cefazolin

Answer

Aztreonam

Answer

Imipenem

Answer

Vancomycin

Question 2

Which mechanism best explains why aminoglycosides exhibit concentration-dependent bactericidal activity?

Accepted Answer

Higher peak concentrations drive greater uptake into bacteria via the electron transport chain

Answer

They irreversibly bind the 50S ribosomal subunit at higher concentrations

Answer

They inhibit DNA gyrase more potently at elevated concentrations

Answer

They competitively inhibit transpeptidase in a concentration-dependent manner

Question 3

A patient on warfarin develops a urinary tract infection. Which antibiotic choice requires the most careful INR monitoring due to interaction with warfarin metabolism?

Accepted Answer

Trimethoprim-sulfamethoxazole

Answer

Nitrofurantoin

Answer

Fosfomycin

Answer

Pivmecillinam

Question 4

Daptomycin is contraindicated for the treatment of Staphylococcus aureus pneumonia because:

Accepted Answer

It is inactivated by pulmonary surfactant

Answer

It does not penetrate the blood-brain barrier

Answer

It is exclusively excreted by the kidneys and causes nephrotoxicity

Answer

It induces beta-lactamase production in S. aureus

Question 5

Which pharmacokinetic property makes once-daily dosing of aminoglycosides advantageous compared to traditional thrice-daily dosing?

Accepted Answer

The post-antibiotic effect allows bacterial suppression between doses

Answer

Improved time-dependent killing reduces total dose needed

Answer

Renal tubular saturation during the trough period reduces nephrotoxicity

Answer

Extended half-life with once-daily dosing avoids peak toxicity

Question 6

A patient receiving prolonged vancomycin therapy develops sensorineural hearing loss. This toxicity is most likely related to which pharmacokinetic parameter?

Accepted Answer

Renal insufficiency causing drug accumulation and high troughs

Answer

Excessively low trough levels

Answer

Elevated vancomycin AUC/MIC ratio

Answer

Concurrent use of loop diuretics increasing peak levels

Question 7

Which statement accurately describes the mechanism of action of linezolid?

Accepted Answer

It binds the 50S subunit at the peptidyl transferase center, preventing initiation complex formation

Answer

It inhibits the 30S ribosomal subunit, preventing tRNA binding

Answer

It inhibits bacterial DNA gyrase and topoisomerase IV

Answer

It disrupts the cytoplasmic membrane via calcium-dependent depolarization