Gentamicin and tobramycin Kinetics.

Eighty-two hospitalized adult patients were randomized to treatment with gentamicin or tobramycin. Serum levels were compared to computer-derived mathematically predicted levels to evaluate predictability of gentamicin and tobramycin serum levels. When comparable dosages were used mean peak gentamicin levels (4.87 micrograms/ml) did not differ from those after tobramycin (4.31 micrograms/ml). Seventy-three percent of patients had peak levels after gentamicin greater than 4.0 micrograms/ml compared to 46% after tobramycin. Factors purported to influence predictability of aminoglycoside serum levels were examined. In 46 of 74 patients whose actual body weight was 10 to 35 kg less than estimated ideal body weight levels after both drugs were lower than predicted. Serum levels were also lower than predicted in 7 of 11 patients with ascites, 6 of 7 patients receiving carbenicillin therapy, and 17 of 29 patients who had pneumonia. Neither hematocrit nor temperature appeared to influence predictability of serum levels. A comparison of methods used to obtain computer-derived predicted levels showed that ideal body weight provided the most accurate prediction. Differences between predicted and measured levels were established when calculations were based on actual body weight (P = 0.009) or on surface area (P = 0.003 for peak and 0.023 for trough levels).

RCT Entities:   Population Interventions Outcomes