The pharmacokinetics of tobramycin in the elderly above 80 years old.

The pharmacokinetics of tobramycin were studied in two groups of elderly people. Sixteen aged people (65-97 years old) participated in the study after giving informed verbal consent. They were divided into two groups: group I consisted of the age group 65-79, and group II consisted of 80-97 years old.Tobramycin was administered intravenously with an infusion pump over lhr. Blood samples (3 ml) were collected at 7 time points via an indwelling catheter placed in the forearm. Serum creatinine, beta-2-microglobulin, and tobramycin concentrations weremeasured. The values obtained were compared between the two groups. Serum creatinine showed no significant differences in the 2 groups, whereas beta-2-microglobulin was significantly higher in group II (3. 35 ± 0.95) than in group I (2.25 ± 0.48). The elimination rate constant of tobramycin was determined from 7 postinfusion serum concentrations using linear regression on a natural logarithm concentration-versus-time graph. Half-life was calculated by dividing the elimination rate constant into 0.693. The half-lives of these 2 groups were 2.5± 0.47 (hr) and 4.2± 1.2 (hr) respectively and they were significantly different. The serum beta-2-microglobulin concentration correlated with the half-life of this drug in all subjects. Due to the large degree of interpatient variability observed, individualization of tobramycin doses using serum concentration monitoring may help to rapidly achieve desired steady-state levels.