A 25-year-old woman develops fever and malaise 3 weeks after starting trimethoprim/sulfamethoxazole for treatment of a urinary tract infection. Her plasma total white count is 7x10 3/cmm, with elevated eosinophils on the differential. Her urinalysis shows many white cells, 2 white cell casts/high powered field, no red cells or casts, trace protein, and no bacterial growth. Her serum creatinine is 1.3 mg/dl. Her erythrocyte sedimentation rate is elevated. The remainder of her laboratory work is normal. What findings are expected on renal biopsy?
a. Interstitial eosinophilic infiltrates
b. Tubulointerstitial nephritis
c. Granulomatous inflammation
d. Minimal change disease