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

First-generation cephalosporins like cefazolin share a similar R1 side chain with some penicillins, conferring the highest cross-reactivity risk among beta-lactams.

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

Aminoglycoside uptake into bacterial cells is energy-dependent and increases with higher drug concentrations, producing a concentration-dependent kill curve.

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

Trimethoprim-sulfamethoxazole inhibits CYP2C9, reducing warfarin metabolism and significantly elevating INR, increasing hemorrhage risk.

Question 4

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

Accepted Answer

It is inactivated by pulmonary surfactant

Answer

Pulmonary surfactant binds and inactivates daptomycin, rendering it ineffective for lung infections.

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

Aminoglycosides exhibit a prolonged post-antibiotic effect (PAE), meaning bacterial growth remains suppressed even after drug levels fall below the MIC.

(MCCQE) Medical Council of Canada Qualifying Examination Practice Test

(MCCQE) Medical Council of Canada Qualifying Examination Practice Test

MCCQE Antimicrobial Pharmacology 2