Comparison of the effects of loperamide and loperamide oxide on absorptive processes in rat small intestine.

Mucosal loperamide inhibited the absorption of glycine by everted sacs of rat small intestine over 10-, 30- or 60-min incubation periods, but loperamide oxide was without effect. In stripped intestinal sheets, loperamide inhibited the rise in short-circuit current associated with Na(+)-linked glucose absorption, but this effect was not observed with loperamide oxide. It is concluded that although there is evidence that loperamide oxide is converted to loperamide in the intestinal lumen, the rate at which free loperamide appears is not sufficient to inhibit absorptive processes.