A 46-year-old male with HIV and severe penicillin allergy receiving zidovudine, indinavir, and stavudine presents with fever, nonproductive cough, and severe hypoxia. Chest x-ray reveals diffuse increased interstitial markings and a possible lobar consolidation in the left lower lobe. After appropriate evaluation, the patient receives levofloxacin, trimethoprimsulfamethoxazole, and acyclovir. Initial serum creatinine is 1.6 mg/dL. On day 4, it has risen to 3.8 mg/dL and a normal serum potassium has risen to 7.1 mg/dL. Urinalysis reveals no casts, 10 to 20 WBC/HPF, and rare RBCs. Which drug is the most likely cause of renal failure?
High-Yield Explanation
In the elderly or in patients with renal insufficiency, full doses of trimethoprimsulfamethonazole frequently cause drug-induced interstitial nephritis and hyperkalemia (due to inhibition of the sodium- potassium transpo system in the distal nephron). Levofloxacin is a very rare cause of renal dysfunction. In the setting of volume depletion, acyclovir may cause acute renal failure secondary to intratubular obstruction from crystal deposition. Crystals are absent from the urine in this case. Indinavir may crystallize and cause either nephrolithiasis or renal failure due to tubular obstruction.