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Antimicrobial Pharmacology Flashcards

7 cards from real MCCQE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A patient with HIV and a CD4 count of 50 cells/µL develops Pneumocystis jirovecii pneumonia. First-line treatment is trimethoprim-sulfamethoxazole (TMP-SMX). Which electrolyte abnormality must be closely monitored?

    Answer: Hyperkalemia due to trimethoprim's amiloride-like effect on the collecting duct

    Trimethoprim blocks epithelial sodium channels in the distal nephron similar to amiloride, reducing potassium excretion and causing hyperkalemia.

  2. Which class of antibiotics acts by inhibiting bacterial cell wall synthesis through binding penicillin-binding proteins (PBPs) and is naturally resistant to beta-lactamases?

    Answer: Carbapenems

    Carbapenems bind PBPs to inhibit cell wall synthesis and have inherent stability against most beta-lactamases due to their unique bicyclic ring structure.

  3. Fluconazole is effective against Candida albicans but often ineffective against Candida krusei. Which mechanism explains this intrinsic resistance?

    Answer: C. krusei has an intrinsically less susceptible CYP51 target enzyme

    Candida krusei has intrinsic resistance to fluconazole primarily due to reduced affinity of its lanosterol 14α-demethylase (CYP51) target for the drug.

  4. A 65-year-old patient on fluoroquinolone therapy develops sudden Achilles tendon rupture. Which mechanism underlies this adverse effect?

    Answer: Fluoroquinolones chelate magnesium in collagen-producing cells, disrupting matrix metalloprotease regulation

    Fluoroquinolones chelate divalent cations like magnesium in tenocytes, disrupting matrix metalloprotease homeostasis and degrading collagen in tendons.

  5. Which antifungal drug works by inhibiting 1,3-beta-D-glucan synthase, disrupting the fungal cell wall?

    Answer: Caspofungin

    Caspofungin is an echinocandin that inhibits 1,3-beta-D-glucan synthase, reducing glucan polymer synthesis in the fungal cell wall.

  6. A patient with Clostridium difficile infection fails metronidazole therapy. What is the most appropriate next step?

    Answer: Start oral vancomycin

    Oral vancomycin is recommended for patients who fail or are intolerant to metronidazole for C. difficile infection, as it achieves high luminal concentrations.

  7. Which antibiotic requires dose adjustment in patients with renal failure but NOT in patients with hepatic failure?

    Answer: Gentamicin

    Gentamicin is almost entirely renally excreted without hepatic metabolism, requiring dose reduction in renal failure but not in hepatic impairment.