Hepatic Disposition of Fexofenadine: Influence of the Transport Inhibitors Erythromycin and Dibromosulphothalein Robert W. Milne, 1,2 Linda A. Larsen, 1 Klaus L. Jørgensen, 1 Jesper Bastlund, 1 Graham R. Stretch, 1 and Allan M. Evans 1 Received April 19, 2000; accepted August 31, 2000. Purpose. To examine the disposition of fexofenadine in the isolated perfused rat liver and the influence of erythromycin and dibromosul- phthalein (DBSP) on the hepatic uptake and biliary excretion of fexofenadine. Methods. Livers from four groups of rats were perfused in a recircu- latory manner with fexofenadine HCl added as a bolus (125, 250, 500, or 1000 g) to perfusate. Livers from another three groups of rats were perfused with 250 g of fexofenadine HCl. With one group as control, erythromycin (4.0 g/ml) or DBSP (136 g/ml) was added to the perfusate of the other groups. In all experiments, perfusate and bile were collected for 60 min; in addition, livers from the second experiment were retained for assay. Fexofenadine was determined in perfusate, bile, and homogenized liver by HPLC. Results. The area under the curve (AUC) of fexofenadine was lin- early related to concentration. It was unchanged from control (12,800 ± 200 ngh/ml) by erythromycin (14,400 ± 2000 ngh/ml), but was increased 95% by DBSP (25,000 ± 2600 ngh/ml, P <0.001). The ratios of the concentrations of fexofenadine in liver/perfusate were de- creased significantly by DBSP; those for bile/liver were increased by erythromycin. Conclusions. Erythromycin reduced the canalicular transport of fexofenadine into bile, whereas DBSP reduced uptake across the sinusoidal membrane. KEY WORDS: fexofenadine; hepatic transport; inhibition; erythro- mycin; dibromosulphothalein. INTRODUCTION Fexofenadine is one of the more recent second- generation H 1 -histamine receptor antagonists approved for the relief of allergic rhinitis. It is the carboxylate metabolite of terfenadine. The latter has been withdrawn from sale in many countries because of concerns over its cardiotoxicity when coadministered with drugs known to inhibit the metabolism of terfenadine to fexofenadine, a path catalyzed by CYP3A4 (1). The cardiotoxicity of fexofenadine appears to be minimal (2). Preliminary observations suggest that, following oral ad- ministration, fexofenadine is eliminated essentially un- changed, with the majority of the dose appearing in feces (about 80%) and around 12% in urine (1,3). Our interest in the hepatic disposition of fexofenadine was stimulated by reports of significant increases in the area under the curve (AUC) of terfenadine and also of fexofena- dine (4–6) when inhibitors of CYP3A4-catalyzed metabolism, such as erythromycin, ketoconazole, itraconazole, and flu- conazole, were coadministered with terfenadine. Some of these inhibitors of CYP3A4, such as erythromycin and keto- conazole, have also been found to inhibit transport catalyzed by P-glycoprotein (7,8). Recent studies have observed a net efflux of fexofenadine from the basolateral to apical side of a monolayer of Caco-2 cells (9); such efflux has been confirmed with layered L-MDR1 cells expressing P-glycoprotein (10). The latter workers also administered fexofenadine intrave- nously and orally to normal mice and mice lacking the mdr1a gene (-/-) and found approximately 5-fold greater concen- trations of fexofenadine in plasma and in tissues of the liver, kidney, and brain of the (-/-) mice. In addition, these work- ers observed saturable cellular uptake of fexofenadine that was mediated by the organic anion transporting protein (OATP). OATP is located in the sinusoidal membrane of hepatocytes, whereas P-glycoprotein is located in the canalic- ular membrane (11). Hence, our hypothesis was that fexofenadine may be ac- tively transported across the sinusoidal membrane into hepa- tocytes via OATP, and secreted into biliary canaliculi via P- glycoprotein. Furthermore, it is possible that substrates for sinusoidal uptake, such as dibromosulphothalein (DBSP) (12), and inhibitors of transport by P-glycoprotein, such as erythromycin (7), may modify the hepatic disposition of fexofenadine. The latter may explain in part the increased AUC of fexofenadine in humans during concurrent adminis- tration of terfenadine or fexofenadine with erythromycin (4,13). Therefore, the aims of our study were to examine the disposition of fexofenadine in the isolated perfused rat liver and investigate the influence of erythromycin and DBSP on the hepatic uptake and biliary excretion of fexofenadine, and on its concentrations within the liver. MATERIALS AND METHODS Chemicals Fexofenadine HCl (lot no. Q00514) was a gift from Hoechst Marion Roussel, Inc. (Bridgewater, NJ). Erythromy- cin was obtained from Sigma Chemical Co. (St. Louis, MO), and DBSP from S.E.R.B. (Paris, France). Acetonitrile (UV cut-off 190 nm, BDH, Poole, England), potassium dihydrogen orthophosphate (AR grade, Ajax Chemicals, Auburn, Aus- tralia), and Milli-Q water were used for HPLC. All other chemicals for the preparation of perfusing media were of ana- lytical grade and used as supplied commercially. Surgery and Perfusion of Livers Male Sprague-Dawley rats (250–350 g, Gilles Plains Ani- mal Resource Centre, Adelaide, Australia) were housed in plastic cages in a room with a 12-h light/dark cycle, and al- lowed free access to water and food (Mouse Cubes, Rigley 1 Centre for Pharmaceutical Research, School of Pharmacy and Medical Science, University of South Australia, Adelaide, Australia 5000. 2 To whom correspondence should be addressed. (e-mail: robert. milne@unisa.edu.au) ABBREVIATIONS: CYP, cytochrome P450; AUC, area under the curve; OATP, human organic anion transporting protein; oatp1, iso- form of rat organic anion transporting protein; cMOAT, canalicular multispecific organic anion transporter; DBSP, dibromosulphthalein; CL b , biliary clearance. Pharmaceutical Research, Vol. 17, No. 12, 2000 Research Paper 1511 0724-8741/00/1200-1511$18.00/0 © 2000 Plenum Publishing Corporation