Transport characteristics of fexofenadine in the Caco-2 cell model

Purpose. To investigate the membrane transport mechanisms of fexofenadine in the Caco-2 model. Methods. Transport studies were performed in Caco-2 cell monolayers 21 - 25 days after seeding. The apparent permeability (P-app) of fexofenadine was determined in the concentration range 10 - 1000 muM in the basolateral-to-apical (b- a) and 50 - 1000 muM in the apical-to-basolateral (a-b) direction. The concentration-dependent effects of various inhibitors of P-glycoprotein (P-gp) (GF120918, ketoconazole, verapamil, erythromycin), multidrug resistant associated protein (MRP) ( indomethacin, probenecid), and organic anion transporting polypeptide (OATP) ( rifamycin SV) on the bidirectional transport of 150 muM fexofenadine were also examined. Results. Fexofenadine displayed polarized transport, with the Pappb-a being 28- to 85-fold higher than the Papp(a-b). The Papp(a-b) was independent of the concentration applied, whereas Pappb-a decreased with increasing concentration (V-max = 5.21 nmol cm(-2)s(-1) and K-M = 150 muM), suggesting saturation of an apical efflux transporter. All four P-gp inhibitors had a strong, concentration-dependent effect on the Papp of fexofenadine in both directions, with GF 120918 being the most specific among them. The IC50 of verapamil was 8.44 muM on the P-gp-mediated secretion of fexofenadine. The inhibitors of OATP or MRP appeared not to affect the Papp(a-b) of fexofenadine in the Caco-2 model. Conclusions. This study clearly indicates that P-gp was the main transport protein of fexofenadine in the Caco-2 model. Even though P-gp was completely inhibited, fexofenadine was predicted to have a low fraction dose absorbed in humans due to poor intestinal permeability, and low passive diffusion seems to be the major absorption mechanism.