[An early and specific indicator of aminoglycoside nephrotoxicity: isoenzyme B of urinary N-acetyl-beta-D-glucosaminidase (NAG)].

88 patients (aged 55-96 years) with severe infections were treated during ten days with one of four different aminoglycosides: gentamicin, dibekacin, netilmicin (3 mg/kg/day) or amikacin (15 mg/kg/day). Creatinine clearance and urinary N-acetyl-glucosaminidase (NAG) activity were measured daily. In addition, NAG isoenzyme patterns were determined on the day of maximal urinary NAG excretion. Aminoglycoside-induced acute renal failure was more prevalent in the gentamicin group (42.8%) than in the dibekacin, netilmicin or amikacin groups (42.8%, 5.5% and 0% respectively). No relationship was found between total urinary NAG activity and nephrotoxic risk. Conversely, significantly elevated levels (p less than 0.001) of B isoenzyme were detected in the gentamicin group, whereas the highest A and I isoenzyme levels were found in the dibekacin and netilmicin groups. These results suggest that functional enzymuria with preferential urinary excretion of A and I isoenzymes should be distinguished from lesional enzymuria with preferential urinary excretion of the B isoenzyme. According to our data, the NAG-B isoenzyme may possibly be a specific marker of aminoglycoside nephrotoxicity.