Study of alanine aminopeptidase excretion as a test of gentamicin nephrotoxicity.

We studied the urinary excretion of the proximal tubular enzyme alanine aminopeptidase (AAP) by 38 patients who received gentamicin and by 45 similar control patients. AAP excretion by the control patients was highly variable. The pattern of AAP excretion distinguished patients with pre-renal and renal causes for increases in serum creatinine (SCr) but this can be done more simply with the urine to serum creatinine ratio. Peak AAP excretion did not reflect renal damage in oliguric patients and di not identify gentamicin patients with a renal cause for increases in SCr. The level of AAP excretion in the first three days of gentamicin treatment did identify the three patients with renal causes for an increase in SCr and was highest in a patient with symptomatic hypomagnesaemia due to impairment of proximal tubular function. We concluded that study of AAP excretion in normal volunteers receiving three-day courses of aminoglycosides is a valid screening test for nephrotoxicity but that AAP excretion is too non-specific to use in clinical practice.