Authors: Lore Bogaert , Roos Pannecoeck , Lisa Florin , Dirk Verleyen

Abstract

Background: Amoxicillin, a commonly used broad-spectrum antibiotic, can crystallize in renal tubules when administered at high doses, causing acute amoxicillin-induced crystal nephropathy (AICN). This condition typically presents with acute kidney injury (AKI) and macroscopic hematuria. Risk factors include high dosage, rapid infusion, dehydration, and low urinary pH. Although urine microscopy can confirm amoxicillin crystals, it is underutilized, contributing to underrecognition of AICN.

Case Report: We present the case of a 75-year-old woman with fever and cellulitis, diagnosed with native aortic valve endocarditis due to Streptococcus dysgalactiae. She was treated with high-dose intravenous amoxicillin (6 × 2 g/day). On day two, she developed macroscopic hematuria and progressive AKI, eventually requiring temporary hemodialysis. Urine microscopy revealed elongated amoxicillin crystals, confirming the diagnosis of AICN. Amoxicillin was discontinued and replaced with continuous penicillin G infusion. Renal function recovered markedly within one week, allowing discontinuation of dialysis.

Discussion: This case highlights the importance of considering AICN in patients receiving high-dose amoxicillin who develop unexplained AKI and hematuria. Urine microscopy is a valuable, non-invasive diagnostic tool and should be more routinely used in suspected cases to enable early detection. Timely diagnosis through urine microscopy is crucial, as discontinuation of amoxicillin can lead to rapid and complete renal recovery.

Keywords: Amoxicillin-induced crystal nephropathy (AICN), high-dose amoxicillin therapy, adverse drug effect, crystalluria; urine microscopy, case report.