Abstract
In bucillamine-treated patients, persistent proteinuria caused by membranous nephropathy (MN) is a major adverse effect affecting the kidneys. We experienced a case of acute interstitial nephritis (AIN) with MN caused by bucillamine. An 81-year-old Japanese woman with a past medical history of rheumatoid arthritis and hypertension presented with a fever, epigastric pain, and nausea of 1 week's duration. She had commenced bucillamine 4 months earlier. At the time of admission, her baseline creatinine (0.8 mg/dl) had risen to 6.8 mg/dl. A renal biopsy revealed AIN with concomitant MN. Renal function gradually improved after bucillamine administration was stopped. In addition to MN, bucillamine can cause AIN, which requires a renal biopsy for definitive diagnosis. Given the host of pathological findings that tend to develop in patients using bucillamine, patients receiving the drug who present with symptoms of acute kidney injury should undergo a renal biopsy to determine the presence of AIN.