Intestinal secretion of erythromycin base.

Erythromycin fluxes into rabbit midjejunal segments were studied. When erythromycin was infused into the jugular vein of anesthetized rabbits, the antibiotic was secreted into the segments at a rate of 0.0136 +/- 0.0023 mg/min. Preloading of the segments with five and 20 times the plasma concentration did not diminish this secretion. Protein binding of the antibiotic within the lumen could not explain this secretion, since both ultrafiltration and chromatography of luminal solutions indicated that the biological activity was free erythromycin. Moreover, the transmural potential across the intestinal mucosa is likely to be theprincipal driving force, since greater than 80 mv would be required to sustain the observed secretion against an imposed 20-fold concentration difference between blood and lumen. The best explanation for the intestinal secretion of erythromycin appears to be an active transport pathway capable of concentrating erythromycin in the lumen. It is not clear what endogenous substances are transported by this pathway.