Antimicrobials USMLE Step 1 Practice Question
A 24-year-old man presents with urethritis and dysuria; urine culture confirms Neisseria gonorrhoeae. He is prescribed ciprofloxacin 500 mg orally twice daily. Vital signs are stable (BP 118/76, HR 82, temp 37°C). At follow-up 1 week later, persistent urethral discharge and dysuria remain; urinalysis shows continued pyuria. He admits taking each dose with a large glass of milk and a calcium supplement. He denies antibiotic allergies. Which of the following best explains treatment failure?
Answer choices
- ACalcium chelates ciprofloxacin, reducing its absorption and bioavailabilityCorrect answer
- BCalcium-resistant Neisseria gonorrhoeae emerged during treatment
- CMilk increases renal excretion of ciprofloxacin before absorption
- DCiprofloxacin requires gastric acid for activation, neutralized by milk
- EMilk proteins induce hepatic metabolism of ciprofloxacin
- FCiprofloxacin penetration into urethral tissue is inhibited by elevated serum calcium levels
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