Patient X is a 72-year-old female admitted for sepsis with gram-negative rod bacteremia. Patient had nausea and vomiting for a day almost 4 days back, which improved, but after that she stayed lethargic with decreased oral intake. She also complained of dysuria and left flank pain so her daughter took her to the primary care doctor where she was found to have leukocytosis and acute renal failure and was sent into the hospital for admission. Blood cultures are positive for gram-negative rods; however, culture and susceptibilities are pending. The urine culture returned the following results:

Ampicillin and trimethoprim-sulfamethoxazole are reported as R and should not be used. Levofloxacin is reported as I. If the patient did not show signs of sepsis, then levofloxacin may be considered since the concentration in the urine is extremely high. However, a 750-mg dose of levofloxacin IV achieves a plasma level of approximately 12 mcg/mL. This would not be sufficient to achieve adequate killing in the plasma and should not be used. Nitrofurantoin is reported as S with an MIC ≤16. While this number may seem high, even at 32, nitrofurantoin achieves a high enough concentration in the urine to be considered for cystitis but does not treat infections such as pyelonephritis or urosepsis. Therefore, nitrofurantoin should not be used. E. coli does not possess any intrinsic resistance, and further workup is not needed unless allergies warrant alternative agents. The remaining antibiotics include two beta-lactams (ceftriaxone and imipenem) and an aminoglycoside, gentamicin. If the infection were only in the urine, either of the three would be fine. However, gentamicin with an MIC of four would be a poor choice for a bloodstream infection. When dosed as 2 mg/kg, the peak plasma level is approximately 8 mcg/mL. When dosed using 7 mg/kg, the peak plasma concentration would be approximately 28 mcg/mL. Both imipenem and ceftriaxone achieve very high plasma levels and would be good options even with the bloodstream infection; however, ceftriaxone has a narrower spectrum and would be preferred. Susceptibilities to tobramycin and amikacin may be requested if an aminoglycoside were needed. Turnaround time is generally 24 hours but should be considered if the patient’s condition worsens.