Antimicrobials USMLE Step 1 Practice Question
A 52-year-old woman with metastatic breast cancer on active chemotherapy presents to the hospital with fever (39.2°C), productive cough, and dyspnea for 3 days. She is immunocompromised with an absolute neutrophil count of 480/μL. Vital signs: HR 112 bpm, RR 22/min, BP 128/76 mmHg, SpO2 94% on room air. Chest X-ray shows bilateral interstitial infiltrates. She has acute kidney injury with serum creatinine 1.8 mg/dL (baseline 0.9 mg/dL) and BUN 32 mg/dL. Empiric therapy with piperacillin-tazobactam and tobramycin was initiated 24 hours ago. A tobramycin trough level drawn just before the third dose is 8 mcg/mL (therapeutic target <1 mcg/mL). Sputum culture and blood cultures are pending. Which of the following is the most appropriate next step in management?
Answer choices
- ADecrease tobramycin dose and extend the dosing interval based on the patient's estimated glomerular filtration rateCorrect answer
- BIncrease the tobramycin dose to 7 mg/kg to achieve therapeutic peak levels of 15-30 mcg/mL
- CContinue the current tobramycin regimen; elevated trough levels will normalize once acute kidney injury resolves
- DDiscontinue tobramycin and add ciprofloxacin for similar gram-negative coverage with renal dosing
- EMaintain piperacillin-tazobactam monotherapy and discontinue all aminoglycosides due to nephrotoxicity risk
- FInitiate emergent hemodialysis to rapidly clear tobramycin and prevent further renal deterioration
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