Antimicrobials USMLE Step 1 Practice Question
A 34-year-old woman without significant past medical history presents with a 3-day history of fever, dyspnea, and productive cough. She reports rust-colored sputum. Vital signs show temperature 39.4°C, blood pressure 98/62 mmHg, heart rate 112 bpm, respiratory rate 24 bpm, and oxygen saturation 88% on room air. Physical examination reveals dullness to percussion and decreased breath sounds at the left lung base. Chest X-ray shows a left lower lobe consolidation. Laboratory studies reveal WBC 18,400/µL with left shift, and procalcitonin 4.2 ng/mL. Blood cultures obtained at admission grow Streptococcus pneumoniae susceptible to penicillin, ceftriaxone, and fluoroquinolones. The patient is started on levofloxacin monotherapy. After 48 hours of therapy, she remains febrile (38.9°C) with worsening hypoxemia requiring supplemental oxygen. Which of the following best explains the inadequate clinical response?
Answer choices
- ARapid development of fluoroquinolone resistance in S. pneumoniae during therapy
- BInadequate levofloxacin penetration into lung parenchyma and pleural fluid
- CS. pneumoniae is intrinsically resistant to fluoroquinolones despite reported susceptibility
- DBeta-lactam antibiotics achieve superior bactericidal activity against pneumococcal bacteremia compared to fluoroquinolone monotherapyCorrect answer
- EThe patient has developed acute respiratory distress syndrome requiring mechanical ventilation rather than antibiotic optimization
- FAspiration of oral anaerobes requiring concurrent anaerobic coverage that fluoroquinolone monotherapy cannot provide
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.