Evaluation of serum gentamicin assay procedures for a clinical microbiology laboratory.

Four methods for the measurement of serum gentamicin concentration were evaluated with respect to cost-effectiveness, accuracy, and precision. Gentamicin concentration was determined in 112 clinical samples by the Staphlococcus epidermidis agar diffusion bioassay procedure in routine service in our laboratory at the time this study was initiated. Appropriate portions of these clinical samples were frozen and later thawed for remeasurement of gentamicin by bioassay or for measurement of gentamicin in one of three other systems. These included the Enzymatic Radiochemical Assay, the Diagnostic Products Corporation Radioimmunoassay and the New England Nuclear Corporation Radioimmunoassay. In addition, gentamicin dissolved in horse serum at 2, 4, 6, 8, 10, and 12 micrograms/ml was aliquoted, frozen, and later thawed for assay in each of the above systems. The data were analyzed for evidence of constant and proportional bias as well as for accuracy and precision.

In vivo studies on the mechanism of action of the tumor inhibitor vernolepin in the Walker 256 carcinosarcoma.

Rats bearing the Walker 256 intramuscular carcinosarcoma were treated intraperitoneally with tritium-labeled vernolepin or with its nontumor-inhibitory methanol adduct. Following treatment with 3H-vernolepin on several different dosage schedules, the tumors were found to contain significantly more radioactivity per gram wet weight than control tissue (muscle from the contralateral limb). After the administration of the nontumor-inhibitory methanol adduct, no such difference was observed. The distribution of radioactivity in various other organs (liver, kidney, spleen, intestine, lung, heat, fat, blood, and brain) was measured following treatment with the parent compound (3H-vernolepin). The implications of these data in terms of the suggested mechanism of action of sesquiterpene lactone tumor inhibitors is discussed.