Antimicrobials USMLE Step 1 Practice Question
A 45-year-old man with a history of orthotopic lung transplantation 3 years ago presents to the hospital with a 2-week history of progressive dyspnea, fever, and nonproductive cough. Chest CT shows diffuse bilateral ground-glass opacities. Transbronchial biopsy reveals large cells with intranuclear inclusions surrounded by a clear halo ("owl's eye" appearance). He is started on ganciclovir 5 mg/kg IV twice daily, but after 10 days of therapy shows clinical deterioration with worsening hypoxemia and rising viral load on PCR. A resistance mutation in viral DNA polymerase is identified. He is switched to an alternative antiviral agent and demonstrates clinical improvement within 48 hours. Which of the following best describes the mechanism of action of the drug used for successful treatment?
Answer choices
- AInhibits viral DNA polymerase after being phosphorylated by viral thymidine kinase
- BInhibits viral DNA polymerase without requiring viral or cellular kinase activationCorrect answer
- CInhibits viral reverse transcriptase by competing with nucleotide substrates
- DInhibits viral integrase by preventing strand transfer reactions
- EInhibits viral protease leading to production of immature non-infectious particles
- FInhibits viral neuraminidase preventing release of progeny virions
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