Cystatin C for gentamicin dosing - a case study.

The study aims to present a case study of a patient with supratherapeutic serum gentamicin concentration. An 83-year-old male was admitted to the Department of Internal Medicine for persistent loss of appetite, decompensated heart failure, and pneumonia. He was treated with 240 mg gentamicin daily alongside ampicillin/sulbactam penicillin antibiotic. The trough gentamicin concentrations and estimated glomerular filtration rate from creatinine (eGFRcrea) and cystatin C (eGFRcys) were performed. The patient had the supratherapeutic trough gentamicin concentration of 2.5 mg/L. eGFRcrea was 62 mL/min/1.73m and eGFRcys was 25 mL/min/1.73m. The difference between eGFRcrea and eGFRcys was 148%. Falsely high eGFRcrea in elderly patient led to the supratherapeutic gentamicin concentration even after the standard 240 mg gentamicin dose.