Acute interstitial nephritis leads to acute renal failure and is usually secondary to drug therapy. We report a case of irreversible, biopsy-proven acute interstitial nephritis in a patient who had received only azithromycin [1].

A 43-year-old man was treated for respiratory infection with azithromycin (250 mg/d for 9 days). Six weeks later he had microscopic hematuria and a serum creatinine level of 530 µmol/L. In 10 days the creatinine level increased to 1141 µmol/L. A renal ultrasound showed no abnormality. Cryoglobulin concentrations, antinuclear antibodies, complement level, cytomegalovirus and Toxoplasma antibodies, serum and urine protein electrophoresis, antibodies to hepatitis A, B, and C, and a rapid plasma reagent test result were normal or negative. His history included pulmonary sarcoid that was inactive for 8 years. He was treated with prednisone but is still using hemodialysis 10 months after the onset of acute renal failure.

Renal biopsy specimens showed acute tubulointerstitial nephritis with developing fibrosis. Light microscopy showed marked polymorphonuclear, eosinophil, and monocyte infiltration of the interstitium with early fibrosis. Immunofluorescence was negative and electron microscopy showed normal glomeruli. No granulomas were seen.

Acute interstitial nephritis is a common cause of acute renal failure, with a growing list of offending agents [2]. Our patient was receiving only azithromycin, which has not been reported to cause acute interstitial nephritis. However, this condition has been reported with erythromycin [3], another macrolide antibiotic. Sarcoidosis was considered as the cause of the condition but was judged unlikely because of the rapid deterioration, absence of active systemic sarcoidosis, and lack of renal granulomas. Typical associated findings of drug-induced acute interstitial nephritis—fever, rash, arthralgia, microscopic hematuria, proteinuria, eosinophilia, and eosinophiluria—may be absent. Withdrawal of the offending drug usually results in recovery; however, as in our patient, permanent renal failure has occurred [4] despite treatment with prednisone [2, 5].