CHARACTERISTIC DIFFERENCE IN GASTROINTESTINAL EXCRETION OF CLARITHROMYCIN AND ROXITHROMYCIN

Excretion characteristics of two new macrolides; clarithromycin and ro xithromycin, into the intestinal and the gastric lumens was studied by in situ single-pass perfusion and loop methods in rats. Roxithromycin maintained higher serum levels than clarithromycin after their intrav enous administrations at a dose of 5 mg kg(-1) each. Radioactivities o f clarithromycin and roxithromycin exsorbed into the intestinal lumen were 8.6 and 18.9% of dose in 2 h, respectively, whereas clarithromyci n and roxithromycin excreted into the bile were 28.4 and 5.9%, respect ively. These results suggest that roxithromycin is transported mainly by exsorption across the intestinal membrane, whereas clarithromycin m ainly by excretion through the biliary tract. On the other hand, radio activities of clarithromycin and roxithromycin exsorbed into the gastr ic lumen were much less then those into the intestinal lumen and were 0.72 and 1.34% of dose in 4 h, respectively. Thus, the exsorption into the gastric lumen seems to be a minor route for the elimination of bo th macrolides. Consequently, the transport into the intestinal lumen v ia the intestinal membrane and/or the bile tract may play a significan t role in the overall elimination of both macrolides. (C) 1998 John Wi ley & Sons, Ltd.