Assay of serum tobramycin levels with the Bactec 460

Comparison of radioimmunoassay with a new immunofluorescent method (FIAX) for measuring tobramycin in serum

A new immunofluorescent method (FIAX) was compared with a radioimmunoassay procedure for the determination of tobramycin serum concentrations. When assaying three tobramycin control sera repeatedly, within-run and run-to-run variations by the FIAX method were all within acceptable limits, and no statistically significant differences were found. Results of 155 sera from patients who had been treated with tobramycin showed a correlation coefficient of 0.93 between the two methods. The FIAX method represents another practical alternative for determining tobramycin serum levels.

Assays of serum aminoglycoside levels by BACTEC 460 in the presence of cefamandole and cefoxitin

The effects of cefamandole and cefoxitin on the assays of serum containing gentamicin, tobramycin, or amikacin by the BACTEC 460 (Johnston Laboratories, Cockeysville, Md.) were studied. The results were analyzed to determine whether the presence of the test substances, cefamandole or cefoxitin, caused a statistically different mean value of aminoglycoside or increase in variance as compared with serum assayed in their absence. The results were then considered in light of medical significance to see whether the difference observed would have any real effect on patient care. The results of each analyses dictate that serum of patients treated with both amikacin and cefamandole be tested in triplicate.