Microbiological assay of bleomycin: Inactivation, tissue distribution, and clearance

Blood, urine, and tissue distributions of Bleomycin in animals and man were studied by microbiological assay using Bacillus subtilis ATCC 6633. Bleomycin was inactivated in vitro by a variety of tissues. Contact of Bleomycin with mouse intestinal or liver homogenates resulted in almost complete inactivation, whereas mouse plasma, kidney, lung, skin, and muscle produced lesser inactivation grossly in that order. Similar trends of inactivation were demonstrated by available human tissues. The present data do not establish whether the inactivation is enzymatic or non‐enzymatic. After single injection of a large dose of Bleomycin into mice, the decrease of plasma level did not follow first order kinetics, indicating that multiple factors are participating in the clearance of the antibiotic. Following the injection of Bleomycin into mice, activity was detected in the skin, lung, and subcutaneously transplanted Ehrlich tumor. Concentrations in liver, intestine, and muscle tissues were too small to detect. Inability to detect activity in the liver and intestine appears to result from inactivation rather than poor distribution of the drug. In general, the concentration of measurable antibiotic was high in tissues where toxicity was described, whereas there was no good correlation between the degree of inactivation of the antibiotic by a tumor tissue in vitro and therapeutic effect in vivo. In man, plasma clearance curves resembled those of mouse plasma. About 50% of injected antibiotic was excreted into the urine in 24 hours. The sensitivity of the method did not permit detailed measurement of the drug levels in various tissues after injection of therapeutic doses of Bleomycin in man.