A 72-year-old woman with chronic kidney disease (baseline creatinine 2.8 mg/dL) and indwelling urinary catheter is admitted with a 3-day history of fever (38.8°C), confusion, and hypotension (BP 82/48 mmHg). She is tachycardic (HR 125/min) and tachypneic (RR 32/min). Laboratory findings: WBC 22,000/μL, lactate 5.8 mmol/L, creatinine 3.9 mg/dL, platelets 85,000/μL. Urine is turbid and foul-smelling. Blood cultures are drawn. After receiving 2 L of normal saline over 1 hour, her BP remains 85/50 mmHg and lactate is still 5.6 mmol/L. What is the next most appropriate step?