Metabolism of 6-[D (-)-α-(4-ethyl-2, 3-dioxo-1-piperazinecarboxamido) phenylacetamido] penicillanic acid (T-1220), a new β-lactam antibiotic, was studied in vivo and in vitro. Only unchanged T-1220 was detected by bioautography in urine of human, monkeys, dogs, rats, and mice receiving T-1220 intramuscularly. When 14C-labeled T-1220 was administered to rats, most of the radioactive product was excreted unchanged in the urine, but two metabolites were detected in a minute amount by autoradiography. These metabolites were identified as 14C-labeled α-{3-[2-(N-ethyl-N-oxaloamino) ethyl] ureido}-benzylpenicillin (14C-T-1220A) and 14C-labeled α-(4-ethyl-2, 3-dioxo-1-piperazinecarboxamido) benzylpenicilloic acid (14C-T-1220B) by thin-layer chromatography, electrophoresis, and high-pressure liquid chromatography. Metabolism of 14C-T-1220 and its mechanism were studied by using high-pressure liquid chromatography for the separation and radioactive measurement for the determination. In the case of the intramuscular administration of 14C-T-1220 to rats, about 92% of the radioactivity was excreted unchanged in urine and bile, but about 94% of the radioactivity in the feces was 14C-T-1220B. The same results were found in rats pretreated with SKF-525A and phenobarbital. In situ studies showed that 14C-T-1220 changed to 14C-T-1220B in the intestinal tracts, and in vitro studies showed that 14C-T-1220 changed to 14C-T-1220B in fecal homogenate. From these results, it seemed that 14C-T-1220 was changed to 14C-T-1220B by β-lactamase produced from intestinal flora.
