Predictive value of urinary N-acetyl-beta-D-glucosaminidase (NAG), alanine-aminopeptidase (AAP) and beta-2-microglobulin (beta 2M) in evaluating nephrotoxicity of gentamicin.

Concentrations of N-acetyl-beta-D-glucosaminidase (NAG), alanine-amino-peptidase (AAP) and beta-2-microglobulin (beta 2M) were determined daily in the urine of 28 patients treated with gentamicin (2-3 mg . kg-1 . day-1) for a mean of 15 days. All had normal renal function. Increased activity in NAG and AAP was observed for all patients, either immediately or after 2 or 3 days of treatment. The results were compared with serum creatinine concentrations and urinary beta 2M levels. This study indicates a relationship between the nephrotoxicity of gentamicin and initial urinary enzymic activity(NAGi) prior to any treatment. The degree of NAG response during the first ten days of treatment appeared as a second prognostic factor. Renal failure was observed for one out of the 12 patients with normal NAGi (NAGi less than 200 mumol/day). Seven of them showed a marked enzyme activity response (greater than 1500 mumol/day) with an increase in beta 2M activity. Eleven out of the 16 patients with elevated NAGi (NAGi greater than 200 mumol/day) developed renal failure and showed an elevated maximal response. The concentration of AAP appears to be of little prognostic value. The variation in individual maximal urinary enzyme responses observed among the 28 patients during the first ten days of treatment points to the existence of individual sensitivities to gentamicin, the exact mechanism of which remains unclear.