[Rare side effect in the treatment of bacterial endocarditis]

A patient went to the hospital due to persistent febrile temperatures. Positive blood cultures for Enterococcus faecalis as well as a vegetation on the mitral valve in the echocardiography were detected. Therefore the diagnosis of E. faecalis endocarditis was made. An appropriate antimicrobial combination therapy with amoxicillin and gentamicin was initiated. During the course of treatment, gentamicin was switched to ceftriaxone because of an acute kidney injury KDIGO stadium AKI 1. Furthermore a mechanical mitral valve replacement was performed. After a continuous 5-week antimicrobial therapy, the patient was urgently transferred back from cardiological rehabilitation to the hospital due to acute flank pain with emesis.Clinically, the 64-year-old patient presented with tenderness in the right abdomen. Laboratory tests revealed acute kidney injury AKI 3 with microhematuria in the urine analysis. Sonographically, there was evidence of hydronephrosis in the right kidney. An abdominal CT revealed a calculus in the urinary bladder.The calculus, measuring 7 × 3 × 2 mm, was expelled through micturition and consisted 100% of amoxicillin. Therefore, the diagnosis of amoxicillin-induced urolithiasis was made.The antimicrobial therapy with amoxicillin was adjusted according to kidney function. Due to an initially unclear inflammatory condition associated with Dressler syndrome, the combination therapy was completed after 8 weeks instead of 6 weeks. At this time, the creatinine level was slightly elevated. After two weeks, it was back within the normal range. Two years later, the patient is free from recurrence of endocarditis.In the case of intrarenal precipitation of crystals, crystal nephropathy occurs, which presents a rare side effect of amoxicillin. As in this case, massive precipitation of macroscopic crystals in the renal pelvis can even lead to urolithiasis with obstructive nephropathy. This case demonstrates the importance of regular monitoring of renal function during treatment with amoxicillin, particularly in high-dose therapy with prolonged treatment duration.