[Isoenzymes of N-acetyl-beta-D-glucosaminidase (NAG): new method of evaluating the nephrotoxicity of aminosides. Our experience with dibekacin in geriatrics]

To evaluate nephrotoxicity of dibekacin among elderly patients, we studied the daily urinary excretion of NAG and determined isoenzyme levels in the urine of 36 patients (mean age 80 yrs) treated with dibekacin (3 mg.kg-1.day-1). Only two patients developed transient acute renal failure during the first 10 days of treatment. Total NAG urinary activity was however important (304.5 +/- 38.6 U/mmol creat), due primarily to isoenzymes A (58.8 +/- 2.0%) and I (30.8 +/- 1.5%), while B-form excretion was moderately increased (10.3 +/- 1.0%). These results were compared with those obtained with gentamicin (28 patients, 11 transient acute renal failure). The rate of A-form was identical for both antibiotics while excretion of the B-form was significantly higher with gentamicin (p less than 0.001). These results show that nephrotoxic risk is linked to the excretion of the B-form, and allow us to oppose the notion of "functional" enzymuria (low nephrotoxic risk) linked with A- and I-forms with the notion of "lesional" enzymuria (high nephrotoxic risk) linked with the B-form.