Macroscopic amoxicillin crystalluria

Abstract

A 62-year-old woman was referred to our hospital in September, 2013, with fever, arthralgia, and dyspnoea lasting for 6 days. Her medical history was uneventful apart from hypertension and active tobacco use. Her glomerular fi ltration rate at admission was 82 mL/min per 1·73 m2 (normal range ≥90 mL/min per 1·73 m2). Blood cultures on admission grew Strepto coccus agalactiae and acute aortic infective endocarditis was rapidly diagnosed with transoesophageal echocardiography. She was immediately started on highdose intravenous amoxicillin (200 mg/kg per day) with intravenous gentamicin (240 mg once-daily). After 4 days, we noticed cloudy urine, with a thin granular appearance (fi gure). Her urine pH was 5·5. Direct examination of the urine showed amoxicillin crystalluria with large, typically aggregated needle-shaped crystals (fi gure) that were birefringent under polarised light microscopy. Her clinical condition worsened with oliguria, acute renal failure, and pulmonary oedema within 24 h. An aortic ring abscess was evident on a second echocardiography. After emergency valve replacement surgery and renal replacement therapy, she recovered well and was discharged home in October, 2013, without further renal replacement therapy, and with improving renal function. Her last glomerular fi ltration rate was 45 mL/min per 1·73 m2 in March, 2014. At last follow-up, in September, 2014, the patient was asymptomatic. Amoxicillin is known to cause urine crystallisation, although its incidence is unknown. Amoxicillin crystalluria usually occurs with high-dose amoxicillin therapy, in urines that have a low pH and are highdensity (mainly due to insuffi cient fl uid intakes). Amoxicillin crystalluria can be microscopic or macroscopic. The typical microscopic appearance described here is usually suffi cient for diagnosis in a compatible context but the amoxicillin composition of these crystals can be confi rmed by infrared spectroscopy if needed. Amoxicillin crystalluria can be asymptomatic or can be responsible for haematuria or acute renal failure attributable to intratubular precipitation or urinary tract obstruction. In our patient, acute renal failure was multifactorial, but we speculate that amoxicillin crystalluria could have played a part. Physicians should be aware of such a complication of amoxicillin because high intravenous doses are frequently prescribed worldwide and because urine alkalinisation and increased fl uid intake might prevent crystalluria.