Quantitative studies on antibiotic nephrotoxicity

Diagnostic potential of urinary enzymes and beta 2-microglobulin in acute urinary tract infection

Urinary excretions of beta 2-microglobulin (beta 2M), N-acetyl-beta-D-glucosaminidase (NAG), alanine aminopeptidase, beta-glucuronidase, acid and neutral alpha-glucosidase as indicators of proximal tubular dysfunction were measured in patients with acute upper and lower urinary tract infection (UTI) and fever of non-renal origin. The sensitivity of beta 2M was 67% and of NAG 49% as assessed in more than 100 episodes of acute pyelonephritis. Combined use of beta 2M and NAG increased the sensitivity to 75%. The degree of beta 2-microglobulinuria and enzymuria was comparable in patients with acute pyelonephritis and fever due to non-renal infections. The excretion of beta 2M and the various enzymes was too variable and unpredictable in individual cases to be useful as diagnostic indicator. In localizing an acute UTI, tests for proximal tubular dysfunction seem to be of no more clinical value than properly measured body temperature.

Urinary alanine aminopeptidase and beta 2-microglobulin as measurements of aminoglycoside-associated renal impairment

The value of urinary alanine aminopeptidase (AAP) and urinary beta 2-microglobulin as predictors of aminoglycoside-associated nephrotoxicity was studied in 46 patients treated with gentamicin or tobramycin. In three patients serum creatinine increased by more than 50 mumol/l. Urinary AAP increased in virtually all patients. The degree of these increases could not be correlated to subsequent increases in serum creatinine. Increases in urinary beta 2-microglobulin were also seen in many patients who did not show subsequent increases in serum creatinine. Moreover, urinary beta 2-microglobulin was elevated before the onset of aminoglycoside treatment in many patients with septicaemia and malignant diseases, thus making an evaluation of antibiotic-induced changes impossible. These results indicate that neither urinary AAP nor urinary beta 2-microglobulin can be used to predict aminoglycoside-associated nephrotoxicity of clinical importance in individual patients.