Two-compartment comparison of gentamicin and tobramycin in normal volunteers

The objective of this study was to determine whether differences in tissue accumulation observed upon multiple dosing of aminoglycosides in hospitalized patients could be identified in appropriate single-dose studies in normal volunteers. Ten volunteers received single intravenous doses of 1.0 mg of gentamicin and tobramycin per kg of body weight in randomized crossover fashion. Multiple serum and urine samples were collected during the next 30 days. Serum aminoglycoside concentrations and urinary excretion rates were fitted to a two-compartment pharmacokinetic model, and parameters were derived. Tobramycin exhibited a higher clearance (P<0.08) and a lower volume of distribution at steady state (P<0.1), neither of which was significant. Tobramycin also showed a significantly lower predicted amount of drug in the body at steady state (P<0.05). These differences are consistent with observations made in patients receiving multiple doses. Single-dose studies appear to be capable of discriminating pharmacokinetic characteristics relevant to the comparative nephrotoxic potential of these two aminoglycosides.