A 72-year-old woman with poorly controlled type 2 diabetes mellitus presents to your clinic one week after being discharged from the hospital. She had been admitted with pyelonephritis secondary to a multi-drug resistant organism, and received several days of intravenous antibiotics. Her serum creatinine on admission had been 2.1mg/dL. Today it is found to be 4.9 mg/dL. Urinalysis reveals rare epithelial casts and no white blood cells. FE_Na is greater than 2%. What antibiotic did she most likely receive during her hospitalization?

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This patient has acute renal failure (ARF) in the setting of chronic kidney disease. Of the drugs listed, amikacin is the most likely causative agent. There are several indications that amikacin or another aminoglycoside is the cause of this patient's acute renal failure. First, she had pyelonephritis with a multidrug-resistant organism, probably a gram-negative rod. Aminoglycosides are commonly used in this setting. Second, her urine sediment does not contain any white blood cells. If she had acute interstitial nephritis (AIN), eosinophils and white blood cell casts would be present in her urine. Third, her elevated FE_Na is not consistent with a pre-renal etiology of acute renal failure. Aminoglycosides may be used in patients with renal dysfunction, but their serum levels and the patient's renal function must be followed closely. Because of their adverse effects and need for monitoring, aminoglycosides are being used with decreasing frequency, particularly in older patients. (Choice A) Nafcillin is a common cause of acute renal failure due to AIN. This drug is used to treat infections caused by methicillin-sensitive Staphylococcus aureus (MSSA). Nafcillin would not have been used to treat multidrug-resistant pyelonephritis and her urinary sediment is not consistent with AIN. (Choice B) Vancomycin is used to treat infections with methicillin-resistant S. aureus (MRSA). MRSA pyelonephritis is uncommon but may occur in patients who are chronically ill, are institutionalized, or have indwelling bladder catheters. Vancomycin can be nephrotoxic at high doses and it must be dosed according to serum levels. This woman is more likely to have been infected with a gram-negative organism than a gram-positive one, so is unlikely to have received vancomycin. (Choice C) Levofloxacin is a fluoroquinolone antibiotic often used to treat pyelonephritis. Levofloxacin must be renally dosed but is not a common cause of ARF. (Choice E) Doxycycline is most often used to treat community acquired pneumonia, some zoonotic infections (e.g., Lyme disease), Chlamydia, and acne. It is not strongly associated with renal dysfunction and is not likely to have been used for multidrug-resistant pyelonephritis. (Choice F) Azithromycin is a macrolide antibiotic typically used to treat community acquired pneumonia, sinus infections, streptococcal pharyngitis, and Chlamydia. It has approximately 20% renal clearance but is not strongly associated with acute renal failure. Educational Objective: Aminoglycosides are antibiotics used to treat serious gram-negative infections. They are potentially nephrotoxic and drugs levels and renal function must be monitored closely during therapy.

A 72-Year-Old Woman with Poorly Controlled Type 2 Diabetes Mellitus