Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 164-188).

<p>The aims of this thesis were to study the in vivo relevance of membrane transporters for intestinal absorption and the hepatic disposition of drugs in humans and preclinical models. Fexofenadine is a substrate for ABCB1 (P-glycoprotein) and members of the organic anion transporting polypeptide (OATP/SLCO) family. It is marginally metabolised in humans. </p><p>The influence of known inhibitors of ABCB1 and OATPs on the membrane transport and pharmacokinetics of fexofenadine was investigated in Caco-2 and porcine models and in humans. The permeability of fexofenadine remained low, even when significantly altered by the addition of an inhibitor. Using the Loc-I-Gut^® technique in vivo in humans, it was possible to see that the jejunal effective permeability of fexofenadine was unchanged when given with verapamil. However, the systemic exposure and apparent absorption rate of fexofenadine increased. This suggests that the first-pass liver extraction of fexofenadine was reduced by verapamil, probably through the inhibition of sinusoidal OATP-mediated and/or canalicular ABCB1-mediated secretion. The unchanged permeability can be explained by simultaneous inhibition of jejunal apical OATP-uptake and ABCB1-efflux, which would leave fexofenadine to be transported by passive trancellular diffusion. A Loc-I-Gut^® perfusion in the porcine model enabling blood sampling in the portal and hepatic veins and bile collection revealed increased jejunal permeability, but no subsequent verapamil-induced elevation in the systemic exposure of fexofenadine. This indicates a species-related difference in the localisation of and/or the substrate specificity of fexofenadine for the transporters involved. The absence of an effect on the first-pass liver extraction in the porcine model might be caused by the observed lower liver exposure of verapamil.</p><p>Finally, a novel intubation technique enabling dosing of fexofenadine in the jejunum, ileum and the colon showed that fexofenadine was absorbed less along the length the intestine in agreement with the properties of a low permeability drug.</p>

The aims of this thesis were to study the in vivo relevance of membrane transporters for intestinal absorption and the hepatic disposition of drugs in humans and preclinical models. Fexofenadine is a substrate for ABCB1 (P-glycoprotein) and members of the organic anion transporting polypeptide (OATP/SLCO) family. It is marginally metabolised in humans. The influence of known inhibitors of ABCB1 and OATPs on the membrane transport and pharmacokinetics of fexofenadine was investigated in Caco-2 and porcine models and in humans. The permeability of fexofenadine remained low, even when significantly altered by the addition of an inhibitor. Using the Loc-I-Gut® technique in vivo in humans, it was possible to see that the jejunal effective permeability of fexofenadine was unchanged when given with verapamil. However, the systemic exposure and apparent absorption rate of fexofenadine increased. This suggests that the first-pass liver extraction of fexofenadine was reduced by verapamil, probably through the inhibition of sinusoidal OATP-mediated and/or canalicular ABCB1-mediated secretion. The unchanged permeability can be explained by simultaneous inhibition of jejunal apical OATP-uptake and ABCB1-efflux, which would leave fexofenadine to be transported by passive trancellular diffusion. A Loc-I-Gut® perfusion in the porcine model enabling blood sampling in the portal and hepatic veins and bile collection revealed increased jejunal permeability, but no subsequent verapamil-induced elevation in the systemic exposure of fexofenadine. This indicates a species-related difference in the localisation of and/or the substrate specificity of fexofenadine for the transporters involved. The absence of an effect on the first-pass liver extraction in the porcine model might be caused by the observed lower liver exposure of verapamil. Finally, a novel intubation technique enabling dosing of fexofenadine in the jejunum, ileum and the colon showed that fexofenadine was absorbed less along the length the intestine in agreement with the properties of a low permeability drug.

Le rein joue un rôle essentiel dans l’élimination des médicaments et de leurs métabolites, de ce fait il assure la défense de l'organisme contre de potentiels xénobiotiques toxiques. Particulièrement, les transporteurs des tubules proximaux rénaux qui ont un rôle dans la sécrétion tubulaire des médicaments. Ainsi, ils sont des déterminants important de la biodisponibilité des xénobiotiques dans l’organisme.Dans cette thèse nous nous sommes intéressés à l’implication des transporteurs rénaux humains hOAT1 et hOAT3 dans des interactions médicamenteuses moyennant des modèles in vitro. Après construction et validation des modèles d’études cellulaires HEK-hOAT1 et HEK-hOAT3, nous avons testé l’effet des inhibiteurs de la pompe à protons sur le transport du méthotrexate par les OATs ainsi que l’effet des antiviraux sur l’influx du tenofovir par ces mêmes transporteurs. Grâce à nos modèles cellulaires nous avons tenté d’expliquer in vitro de probables interactions médicamenteuses décrites en clinique. / The kidney plays an essential role in the elimination of drugs and their metabolites, thus it ensures the defense of the body against potential toxic xenobiotic. Particularly, the secretory transporters in the proximal tubule are major determinants of the disposition of xenobiotic in the body.In this thesis we investigated the involvement of human organic anions transporters hOAT1 and hOAT3 in drug drug interactions through study on in vitro cell models. After construction and validation of cells models studies HEK-hOAT1 and HEK-hOAT3, we tested the effect of proton pump inhibitors on methotrexate transport by OATs and the effect of antivirals on the influx of tenofovir by these two transporters. With our models we tried to explain in vitro probable drug interactions described in the clinic.