A 59-year-old man undergoes coronary bypass surgery. He receives vancomycin prophylactically for 24 hours. On the ninth postoperative day, he develops a fever of 39.8degC (103degF) with a heart rate of 115 beats/min and a blood pressure of 105/65 mm Hg. The surgical site is healing well with no redness or discharge. His white blood cell count is 14,000/mm3 and urinalysis reveals many white blood cells per high-power field. Blood and urine cultures grow a non-lactose-fermenting oxidase-positive gram-negative rod. Which of the following antibiotics is most appropriate to treat this infection?

The patient has a health care-associated UTI complicated by gram-negative bacteremia. The complete identification of gram-negative rods might take 48 hours. Knowing the ability of the growing bacteria to ferment lactose might help in the early prediction of the likely pathogen at hand. Among lactose fermenting gram-negative rods, Enterobacteriaceae such as E coli are most common. Among non-lactose-fermenting oxidase-positive gram-negative bacteria, Pseudomonas aeruginosa is most common. Ceftriaxone, imipenem, and trimethoprim- sulfamethoxazole can be used to treat UTIs while moxifloxacin and tigecycline do not achieve high enough concentration in urine to be used for this indication. Of the listed antibiotics, imipenem, which is a carbapenem beta-lactam antibiotic, is the only one with anti-pseudomonal activity. Antibiotics with anti-pseudomonal activity include certain penicillin (piperacillin/tazobactam and ticarcillin/clavulanate), cephalosporins (ceftazidime and cefepime), carbapenems (imipenem, meropenem, and doripenem), fluoroquinolones (ciprofloxacin and levofloxacin), and aminoglycosides (gentamicin, tobramycin, and amikacin).