Renal disposition of moxalactam in experimental animals as revealed by stop-flow analysis

The mechanisms of moxalactam excretion were studied by stop-flow analysis in dogs, monkeys, and rabbits. In dogs, the amount of moxalactam excreted in the urine was almost equal to that estimated by glomerular filtration. There was no specific moxalactam peak corresponding to the p-aminohippuric acid (PAH) peak in the stop-flow patterns of the dogs. The PAH peak disappeared with administration of probenecid, but the moxalactam stop-flow pattern showed no change. In monkeys, no specific moxalactam peak corresponding to the PAH peak could be detected. In the stop-flow pattern of the rabbit, the peak moxalactam concentration corresponded with that of PAH and disappeared with probenecid. These results suggest that in dogs and monkeys renal excretion of moxalactam takes place mostly through glomerular filtration. In rabbits, however, there is a small renal tubular secretory component added to the primary element, glomerular filtration. These observations point to differences in the mechanisms of moxalactam excretion in different animal species.