Added tag for NBME form 11 b/c this card directly answers the question, see below:
Four days after admission to the hospital for management of cellulitis of the right lower extremity, a 70-year-old woman has an increased serum creatinine concentration. She has type 2 diabetes mellitus. Her medications are glipizide and a multivitamin; she also has received intravenous nafcillin since admission. She is retired from the military. Vital signs are within normal limits. Examination of the trunk shows no abnormalities. There is edema, erythema, and warmth of the right lower extremity. Examination of the left lower extremity shows no abnormalities. On admission, her serum creatinine concentration was 0.9 mg/dL.
Today, laboratory studies show:
Hemoglobin 11 g/dL
Hemoglobin A 7.5%
Leukocyte count 15,000/mm
Segmented neutrophils75%
Bands 1%
Eosinophils 8%
Lymphocytes 14%
Urea nitrogen 60 mg/dL
Creatinine 2.3 mg/dL
Which of the following is the most likely diagnosis?
Answer: Acute interstitial nephritis