Antibiotic concentrations in the urine from kidneys of unequal function.

Little attention has been given to whether an effective concentration of an antibiotic is obtained in the urine of a patient without azotemia who has one poorly functioning kidney and a contralateral normal kidney. This study was undertaken to measure the concentration of various antibiotics in the urine from both kidneys of 20 patients with unilateral renal disease and a radiologically and functionally normal contralateral kidney. Prior to ureteric catheterization each patient received a single parenteral dose of an antibiotic. The peak urinary drug concentration from the damaged kidney per unit of its creatinine clearance exceeded that for the normal kidney for 11/13 patients treated with an aminoglycoside and 6/7 given a cephalosporin. The most severely damaged kidney had a creatinine clearance of 0.6 ml/min. This patient received sisomicin and the peak urinary concentration was only 1.8 micrograms/ml. If a damaged kidney has a creatinine clearance less than 10-15 ml/min it would seem more appropriate to use a cephalosporin rather than an aminoglycoside antibiotic.