Antimicrobials USMLE Step 1 Practice Question
A 58-year-old woman is brought to the emergency department with fever, rigors, and altered mental status for the past 12 hours. Her temperature is 39.4°C, blood pressure is 88/60 mmHg, heart rate is 118/min, and respiratory rate is 22/min. She has a urinary tract infection as the presumed source, and blood cultures subsequently grow Escherichia coli, confirming bacteremia with sepsis. She is resuscitated with intravenous fluids and started on gentamicin 5 mg/kg IV once daily. Serum drug levels obtained at appropriate intervals reveal a peak gentamicin concentration of 18 μg/mL and a trough of 2 μg/mL. Her serum creatinine is 0.9 mg/dL, and audiometric evaluation reveals normal hearing bilaterally. Which of the following best describes the rationale for once-daily dosing of aminoglycosides?
Answer choices
- AAminoglycosides have a 24-hour duration of action, eliminating the need for divided doses
- BOnce-daily dosing reduces bacterial resistance development compared to divided doses
- COnce-daily dosing prevents accumulation-related ototoxicity by maintaining trough levels <1 μg/mL
- DOnce-daily dosing achieves higher peak levels with bactericidal activity while maintaining adequate trough levels to allow renal clearanceCorrect answer
- EOnce-daily dosing reduces protein binding, increasing free drug concentration
- FOnce-daily dosing maximizes the post-antibiotic effect of aminoglycosides, allowing growth suppression without continuous drug exposure
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