Renal toxicity during therapy with gentamicin or tobramycin

Twenty-seven patients who had normal pretherapy renal clearance by the [125I]iothalamate test were randomly assigned either gentamicin or tobramycin for therapy of infections due to susceptible bacteria. No patients were critically ill or had evidence of bacteremia. Mean age and duration of therapy were 51 years and 14 days, respectively, for 15 patients treated with gentamicin, and 45 years and 13 days for 12 patients treated with tobramycin. At the completion of therapy, six (40%) gentamicin and seven (58%) tobramycin patients had a decrease in renal clearance of at least 14% below baseline. The mean decrease was 26% in the gentamicin group and 23% in the tobramycin group. Simultaneous increases in serum creatinine concentrations (greater than or equal to 0.2 mg/dl) occurred in only 4 (31%) of the 13 patients. Of four patients who had renal clearance studies repeated 3 weeks to 6 months after therapy, two had stable function, but at 16 to 19% below baseline. Mean urinary concentration of N-acetyl glucosaminidase and alanine aminopeptidase increased faster and to higher levels with gentamicin than with tobramycin. However, on an individual patient basis, they were not predictive of a decrease in renal clearance in either therapy group.