MCCQE Antimicrobial Pharmacology 5

Question 1

A patient with Type 1 diabetes presents with a diabetic foot infection. Wound culture grows Pseudomonas aeruginosa. Which antibiotic has reliable anti-pseudomonal activity?

Accepted Answer

Piperacillin-tazobactam

Answer

Piperacillin-tazobactam has reliable anti-pseudomonal activity because piperacillin's ureidopenicillin structure allows it to penetrate Pseudomonas's outer membrane.

Question 2

Which antifungal mechanism of action is shared by both fluconazole and voriconazole?

Accepted Answer

Inhibition of lanosterol 14α-demethylase (CYP51)

Answer

Both fluconazole and voriconazole are azoles that inhibit fungal CYP51 (lanosterol 14α-demethylase), blocking ergosterol biosynthesis.

Question 3

A patient with renal failure is prescribed imipenem-cilastatin. Why is cilastatin included in this formulation?

Accepted Answer

It inhibits renal dehydropeptidase-I, preventing imipenem hydrolysis in the kidney

Answer

Cilastatin inhibits dehydropeptidase-I on the renal brush border, preventing hydrolysis of imipenem to a nephrotoxic metabolite and increasing urinary drug levels.

Question 4

Gray baby syndrome associated with chloramphenicol in neonates is caused by which mechanism?

Accepted Answer

Immature hepatic UDP-glucuronosyltransferase causes toxic drug accumulation

Answer

Neonates have immature hepatic glucuronidation (UDP-glucuronosyltransferase), causing chloramphenicol to accumulate to toxic levels, resulting in cardiovascular collapse.

Question 5

A patient on isoniazid (INH) for latent TB prophylaxis develops peripheral neuropathy. Which supplement should be co-administered with INH to prevent this complication?

Accepted Answer

Vitamin B6 (pyridoxine)

Answer

INH competitively inhibits pyridoxal phosphate (active vitamin B6) metabolism, causing deficiency that leads to peripheral neuropathy; pyridoxine supplementation prevents this.

(MCCQE) Medical Council of Canada Qualifying Examination Practice Test

(MCCQE) Medical Council of Canada Qualifying Examination Practice Test

MCCQE Antimicrobial Pharmacology 5