Quantitative evaluation of the function of small intestinal P-glycoprotein:: Comparative studies between in situ and in vitro

Purpose. The extent of intestinal absorption of MDR1 P-glycoprotein (P-gp) substrate drugs may be affected by interindividual differences in the expression level of P-gp, and/ or by simultaneously administered P-gp substrates/inhibitors. The purpose of the present study is to examine whether the extent to which the intestinal absorption is affected by P-gp can be predicted from in vitro experiments. Methods. The in situ intestinal perfusion experiments were performed for 12 compounds in mdr1a/1b (-/-) and normal mice to determine the permeability-surface area ( PS) product. Thus determined intestinal P-gp function was compared with the in vitro P-gp function, which was determined by comparing the transcellular transport across human P-gp expressing and parental LLC-PK1 monolayers. Results. In situ experimental results revealed that the extent to which the intestinal absorption is affected by P-gp was in the following order; quinidine > ritonavir > loperamide, verapamil, daunomycin > digoxin, cyclosporin A > dexamethasone, and vinblastine. A significant correlation was observed between P-gp function determined in the intestinal perfusion and that in LLC-PK1 monolayers. Conclusion. The in vitro transcellular transport across P-gp expressing monolayers may be used to predict the extent to which the intestinal absorption is affected by P-gp.