Antimicrobials USMLE Step 1 Practice Question
A 19-year-old woman presents to the emergency department with fever (39.4°C), severe headache, neck stiffness, and photophobia. Vital signs show BP 116/74, HR 105, RR 22, SpO2 99% on room air. Blood cultures and CSF analysis are pending. She is currently taking an oral contraceptive (ethinyl estradiol/levonorgestrel) with perfect adherence. Empiric treatment for bacterial meningitis is initiated with ceftriaxone, vancomycin, and rifampin. CSF results confirm Neisseria meningitidis sensitive to all agents. Two weeks later, her contraceptive method fails despite continued perfect adherence and no missed doses. Which of the following best explains the contraceptive failure in this patient?
Answer choices
- ARifampin induces hepatic CYP3A4 and other cytochrome P450 enzymes, increasing first-pass metabolism of ethinyl estradiolCorrect answer
- BCeftriaxone disrupts intestinal flora and reduces enterohepatic circulation of estrogen metabolites
- CVancomycin inhibits hepatic metabolism of oral contraceptive hormones, paradoxically reducing serum levels
- DRifampin competitively inhibits intestinal absorption of oral contraceptive pills in the duodenum
- EThe combination of three antibiotics creates a synergistic effect that directly inactivates ethinyl estradiol in the gastrointestinal tract
- FVancomycin induces expression of sex hormone-binding globulin, increasing protein binding and reducing free hormone bioavailability
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