Further investigations on the transport mechanism of cephalexin and ampicillin across rat jejunum.

The transport mechanisms of cephalexin (CEX) and ampicillin (AB-PC) across rat jejunum were examined using the electrophysiological technique in vitro. From the experiments under the short-circuit condition, it became evident that the specific transport system participates in the mucosal-to-serosal transport of CEX, while AB-PC is transport only by the simple diffusion. In addition, the transport routes of these drugs were examined using the voltage-clamp technique. Salicylate, a model drug of the weak electrolyte, was transported mainly via a paracellular route, while CEX, in the absence of Na, penetrated the membrane via two routes, i.e. the transcellular route and the paracellular route. Similar result was obtained as to AB-PC. So it seems to be likely that these two drugs diffuse through the intestinal epithelium via the similar pathways in the Na-free condition.