CONTRIBUTION OF PASSIVE TRANSPORT MECHANISMS TO THE INTESTINAL-ABSORPTION OF BETA-LACTAM ANTIBIOTICS

Abstract— The transport characteristics of aminopenicillins (ampicillin and amoxicillin), aminocephalosporins (cephalexin, cephradine and cefadroxil) and cefazolin have been compared with those of an actively transported substance (D‐glucose) and a passively transported substance (L‐glucose). Although the initial uptake of the aminocephalosporins was stimulated in the presence of an inward H+ gradient, there was no overshoot in the uptake of any of the drugs tested, even in the presence of an H+ gradient. Also, the time course and the degree of uptake of these drugs were similar to those of L‐glucose, especially in the absence of an H+ gradient. These results suggest that the β‐lactam antibiotics tested, like L‐glucose, pass through the rat intestinal brush border membrane mainly by passive diffusion. However, the differences in absorption between these drugs, like the differences in their disappearance from a proximal loop of rat intestine, cannot be explained by a simple permeation process alone. 1990 Royal Pharmaceutical Society of Great Britain