Effect of fat substitutes, sucrose polyester and tricarballylate triester, on digitoxin absorption in the rat.

The effect of non-absorbable fat substitutes (sucrose polyester (SPE) and tricarballylate triester (TCTE)) on [3H]digitoxin intestinal absorption was studied in the rat using a small intestine in-situ perfusion technique. The effect of SPE and TCTE was compared with that of sunflower oil, oleic acid, and saline. After 120 min perfusion, 5% SPE emulsion significantly reduced (P < 0.001) digitoxin absorption compared with all other treated groups. Five per cent TCTE emulsion had a less marked effect than SPE (P = 0.0002) and did not differ from sunflower oil. No difference was found between saline and 5% oleate emulsion, which did not reduce digitoxin absorption compared with other treated groups (P < 0.02). When taurocholic acid and lipase were added, results for the saline-, TCTE-, and SPE-treated groups were similar to those above, but the sunflower oil-treated group showed significantly enhanced (P < 0.01) digitoxin absorption. Thin-layer chromatography of the lipid phases showed hydrolysis of sunflower oil in the presence of taurocholic acid and lipase, but not of TCTE or SPE. The inhibitory effect of the non-absorbable fat substitutes on digitoxin absorption could be related to drug sequestration by the persistent oil phase constituted by the undigested and then unabsorbed fat substitutes. That part of digitoxin dissolved in the undigested oil phase is consequently unavailable for intestinal absorption.