Abstract
In order to investigate the reasons why the body fluid concentrations of pivampicillin and amoxicillin were higher than those of ampicillin after administration of the drugs to rats and humans, the mechanisms of intestinal absorption of these antibiotics in rats were examined using the new fluorometric determination method. In these experiments, it was found that the higher lipid solubility and the greater dissolution rate of pivampicillin are the main reasons for the higher body fluid concentrations of ampicillin after administration of pivampicillin. However, the higher body fluid concentrations of amoxicillin could not be explained on the basis of these physicochemical properties. In the studies using the rat small intestinal segments, i.e. the everted intestine, everted sac and the intact intestinal loop, greater binding to the mucosa of amoxicillin than of ampicillin was observed. This observation may provide an explanation for the difference in body fluid concentrations of these two drugs. These two amphoteric penicillins may be absorbed from the rat small intestine by passive diffusion mechanism.
