Disposition of lipid-based formulation in the intestinal tract affects the absorption of poorly water-soluble drugs

Solvent Green 3 (SG), a model poorly water-soluble compound, was orally administered to rats with soybean oil emulsion or the Self-microemulsifying drug delivery system (SMEDDS) composed of Gelucire44/14. The bioavailability of SC after oral administration with SMEDDS was 1.7-fold higher than that with soybean oil emulsion. The intestinal absorption of lipid-based formulations themselves was evaluated by the in situ closed loop method. The effect of lipase and bile salt on their absorption was also evaluated. SMEDDS itself was rapidly absorbed in the intestine even in the absence of lipase and bile salt, and the absorption was increased by the addition of lipase and bile salt. On the other hand, no soybean oil emulsion was absorbed in the absence of lipase and bile salt. However, mixed micelle prepared from emulsion by incubating soybean oil emulsion with lipase and bile salt was rapidly absorbed through the intestine. Without lipase and bile salt, SG was not absorbed after administration with soybean oil emulsion. Therefore, we concluded that the degradation of soybean oil emulsion was needed for SG to be absorbed through the intestine. Furthermore, we investigated the intestinal absorption of SG after oral administration to rats whose chylomicron synthesis were inhibited by pretreatment with colchicine. Colchicine completely inhibited the intestinal absorption of SC after administration with each lipid-based formulation, suggesting that SG was absorbed from the intestine via a lymphatic route. Absorption of the dosage formulation should be paid attention when poorly water-soluble drugs are orally administered with lipid-based formulation.