Uptake Of Fexofenadine Research Articles

Evaluation of the Effects of Extracts Containing Valeriana officinalis and Piper methysticum on the Activities of Cytochrome P450 3A and P-Glycoprotein.

This work investigated interactions ascribed to the administration of phytomedicines containing Valeriana officinalis and Piper methysticum with conventional drugs. The phytomedicines were characterized by HPLC and administered per os to male Wistar rats, either concomitantly or not with the CYP3A substrate midazolam. To distinguish between the presystemic or systemic effect, midazolam was given orally and intravenously. The effects on the P-gp substrate fexofenadine uptake by Caco-2 cells were examined. The valerenic acid content was 1.6 ± 0.1 mg per tablet, whereas kavain was 13.7 ± 0.3 mg/capsule. Valerian and kava-kava extracts increased the maximum plasma concentration (Cmax) of midazolam 2- and 4-fold compared to the control, respectively. The area under the plasma concentrations versus time curve (AUC(0-∞)) was enhanced from 994.3 ± 152.3 ng.h/mL (control) to 3041 ± 398 ng.h/mL (valerian) and 4139 ± 373 ng.h/mL (kava-kava). The half-life of midazolam was not affected. These changes were attributed to the inhibition of midazolam metabolism by the enteric CYP3A since the i. v. pharmacokinetic of midazolam remained unchanged. The kava-kava extract augmented the uptake of fexofenadine by 3.5-fold compared to the control. Although Valeriana increased the uptake of fexofenadine, it was not statistically significant to that of the control (12.5 ± 3.7 ng/mg protein vs. 5.4 ± 0.3 ng/mg protein, respectively). Therefore, phytomedicines containing V.officinalis or P. methysticum inhibited the intestinal metabolism of midazolam in rats. Conversely, the P-gp-mediated transport of fexofenadine was preferably affected by kava-kava.

Comparison of the transport kinetics of fexofenadine and its pH dependency among OATP1A2 genetic variants

Little is known about the influence of non-synonymous genetic variations in the organic anion-transporting polypeptide (OATP) 1A2 on the transport kinetics of its substrate fexofenadine. Moreover, the pH-dependency of fexofenadine uptake also remains unclear. This study aimed to evaluate the effects of genetic variants (Ile13Thr, Asn128Tyr, Glu172Asp, Ala187Thr, and Thr668Ser) on the OATP1A2-mediated uptake of fexofenadine at pH 6.3 and 7.4 and compare the pH dependency of OATP1A2-mediated uptake of fexofenadine and estrone 3-sulfate. The uptake clearances of 0.3 μM and 300 μM fexofenadine were compared with those of 0.3 μM and 300 μM estrone 3-sulfate at pH 6.3 and 7.4. Among the six variants examined, the Thr668Ser variant showed the highest fexofenadine uptake clearance (Vmax/Km); i.e., 4.53- and 6.28-fold higher uptake clearance than the wild type at pH 6.3 and 7.4, respectively. All variants exhibited significantly higher fexofenadine uptake at pH 6.3 than at pH 7.4. Compared with estrone 3-sulfate uptake, the uptake of 0.3 μM fexofenadine was less sensitive to pH. Our findings suggest that genetic variations in OATP1A2 may lead to altered intestinal absorption of fexofenadine, such as increased absorption in subjects bearing the Thr668Ser variant, which showed higher uptake activity.

Exposure of Fexofenadine, but Not Pseudoephedrine, Is Markedly Decreased by Green Tea Extract in Healthy Volunteers.

Green tea (GT) alters the disposition of a number of drugs, such as nadolol and lisinopril. However, it is unknown whether GT affects disposition of hydrophilic anti‐allergic drugs. The purpose of this study was to investigate whether pharmacokinetics of fexofenadine and pseudoephedrine are affected by catechins, major GT components. A randomized, open, 2‐phase crossover study was conducted in 10 healthy Japanese volunteers. After overnight fasting, subjects were simultaneously administered fexofenadine (60 mg) and pseudoephedrine (120 mg) with an aqueous solution of green tea extract (GTE) containing (−)‐epigallocatechin gallate (EGCG) of ~ 300 mg or water (control). In vitro transport assays were performed using HEK293 cells stably expressing organic anion transporting polypeptide (OATP)1A2 to evaluate the inhibitory effect of EGCG on OATP1A2‐mediated fexofenadine transport. In the GTE phase, the area under the plasma concentration‐time curve and the amount excreted unchanged into urine for 24 hours of fexofenadine were significantly decreased by 70% (P < 0.001) and 67% (P < 0.001), respectively, compared with control. There were no differences in time to maximum plasma concentration and the elimination half‐life of fexofenadine between phases. Fexofenadine was confirmed to be a substrate of OATP1A2, and EGCG (100 and 1,000 μM) and GTE (0.1 and 1 mg/mL) inhibited OATP1A2‐mediated uptake of fexofenadine. On the contrary, the concomitant administration of GTE did not influence the pharmacokinetics of pseudoephedrine. These results suggest that intake of GT may result in a markedly reduced exposure of fexofenadine, but not of pseudoephedrine, putatively by inhibiting OATP1A2‐mediated intestinal absorption.

Effect of Rumex Acetosa Extract, a Herbal Drug, on the Absorption of Fexofenadine.

Herbal drugs are widely used for the auxiliary treatment of diseases. The pharmacokinetics of a drug may be altered when it is coadministered with herbal drugs that can affect drug absorption. The effects of herbal drugs on absorption must be evaluated. In this study, we investigated the effects of Rumex acetosa (R. acetosa) extract on fexofenadine absorption. Fexofenadine was selected as a model drug that is a substrate of P-glycoprotein (P-gp) and organic anion transporting polypeptide 1A2 (OATP1A2). Emodine—the major component of R. acetosa extract—showed P-gp inhibition in vitro and in vivo. Uptake of fexofenadine via OATP1A2 was inhibited by R. acetosa extract in OATP1A2 transfected cells. A pharmacokinetic study showed that the area under the plasma concentration–time curve (AUC) of fexofenadine was smaller in the R. acetosa extract coadministered group than in the control group. R. acetosa extract also decreased aqueous solubility of fexofenadine HCl. The results of this study suggest that R. acetosa extract could inhibit the absorption of certain drugs via intervention in the aqueous solubility and the drug transporters. Therefore, R. acetosa extract may cause drug interactions when coadministered with substrates of drug transporters and poorly water-soluble drugs, although further clinical studies are needed.

Organic anion transporting polypeptide1A2 mediates fentanyl uptake in cultured cells.

Individual differences in the response to fentanyl, which may be caused by different concentrations of the drug in the central nervous system, can complicate analgesic treatment. It has been reported that the organic anion transporting polypeptide(OATP) at the blood‑brain barrier(BBB) in Sprague‑Dawley rats may serve an important role in the transport of fentanyl across the BBB. However, whether human OATP can transport fentanyl has thus far not been reported. The present study aimed to establish a 293cell line stably overexpressing OATP1A2, and to determine whether OATP1A2 is able to transport fentanyl across the plasma membrane. Initially, 293cells were transfected with an OATP1A2‑expressing plasmid (referred to as 293‑OATP1A2 cells), and single colonies were selected and characterized following geneticin treatment. Subsequently, reverse transcription‑quantitative polymerase chain reaction and western blot analyses were conducted to verify the transfection efficiency. Furthermore, treatment of 293‑OATP1A2 cells with different concentrations of fexofenadine (FEX) and fentanyl was performed to investigate the transport function of OATP1A2 in 293cells. FEX and fentanyl uptake experiments were also performed with naringenin, an inhibitor of OATP1A2. The results indicated that FEX and fentanyl uptake was significantly increased in 293‑OATP1A2 cells compared with that in the control‑transfected cells. The 293‑OATP1A2‑mediated uptake of FEX at concentration of 100nM FEX was ~10‑fold higher than that of 293‑VCcells. The 293‑OATP1A2‑mediated uptake of fentanyl (100nM) was 5.1‑fold higher compared with that in 293‑VCcells. In 293‑OATP1A2 cells, the uptake of FEX without OATP1A2 inhibitor naringenin (100µg/ml) was 2.8‑fold higher compared with that in the presence of naringenin, and the uptake of fentanyl without naringenin was 7.3‑fold higher compared with that in the presence of naringenin (100µg/ml). In conclusion, 293cells that overexpressed OATP1A2 were successfully constructed, and OATP1A2 was revealed to mediate fentanyl uptake in the cultured cells.

Drug interaction between shoseiryuto extract or catechins and fexofenadine through organic-anion-transporting polypeptide 1A2 In vitro

Objective: Fexofenadine is an anti-allergy drug frequently used to treat rhinitis, which is absorbed through organic-anion-transporting polypeptide (OATP) 1A2 in the intestine. Clinical studies have revealed that grapefruit juice inhibits OATP1A2 to reduce the absorption of fexofenadine. In Japanese traditional Kampo medicine, shoseiryuto, a formula composed of eight crude drugs, is frequently used to treat allergic rhinitis, especially cases of pollinosis. The objective of this study is to present the drug information regarding the interaction between shoseiryuto and fexofenadine through OATP1A2. Materials and Methods: We established human embryonic kidney 293 cells stably expressing OATP1A2 and evaluated the inhibitory effects of the extracts of shoseiryuto and its herbal components on the uptake of fexofenadine into the cells. Results: Shoseiryuto extract inhibited fexofenadine uptake in a concentration-dependent manner with an IC50 value of 238 μg/ml. The inhibitory titer of shoseiryuto was much lower than that of grapefruit juice, and it is predicted that shoseiryuto could not pharmacokinetically interact interaction with fexofenadine through OATP1A2. Among the eight herbal components of shoseiryuto, the extracts of the terrestrial stem of Ephedra sinica and the root and stolon of Glycyrrhiza uralensis inhibited fexofenadine uptake with IC50 values of 102 and 89 μg/ml, respectively. We isolated catechin as the active ingredient from the extract of the terrestrial stem of E. sinica. Catechins inhibited the uptake of fexofenadine in a concentration-dependent manner, and the IC50 values of epicatechin (EC) gallate, epigallocatechin (EGC) gallate, EGC, catechin, and EC were 11, 26, 41, 52, and 96 μM, respectively. Conclusion: These results would contribute to the safe and effective use of shoseiryuto in clinics. Abbreviations used: CYP: Cytochrome P450; JPXVII: The 17th Edition of the Japanese Pharmacopoeia; EC: Epicatechin; ECG: Epicatechin gallate; EGC: Epigallocatechin; EGCG: Epigallocatechin gallate; HBSS: Hanks' balanced salt solution; HEK: Human embryonic kidney; OATP: Organic-anion-transporting polypeptide; PBS: Phosphate-buffered saline; PHB: p-hydroxybenzoic acid butyl ester.

Functional ATP-Binding Cassette Drug Efflux Transporters in Isolated Human and Rat Hepatocytes Significantly Affect Assessment of Drug Disposition

Freshly isolated hepatocytes are considered the gold standard for in vitro studies of hepatic drug disposition. To ensure a reliable supply of cells, cryopreserved human hepatocytes are often used. ABC-superfamily drug efflux transporters are key elements in hepatic drug disposition. These transporters are often considered lost after isolation of hepatocytes. In the present study, the expression and activity of ABC transporters BCRP, BSEP, P-gp, MRP2, MRP3, and MRP4 in human and rat cryopreserved hepatocytes were investigated. In commercially available human cryopreserved hepatocytes, all drug efflux transporters except human BCRP (hBCRP) exhibited similar expression levels as in fresh liver biopsies. Expression levels of hBCRP were 60% lower in cryopreserved human hepatocytes than in liver tissue, which could lead to, at most, a 2.5-fold reduction in hBCRP-mediated efflux. Fresh rat hepatocytes showed significantly lower levels of rat BCRP compared with liver expression levels; expression levels of other ABC transporters were unchanged. ABC transporters in human cryopreserved cells were localized to the plasma membrane. Functional studies could demonstrate P-gp and BCRP activity in both human cryopreserved and fresh rat hepatocytes. Inhibiting P-gp-mediated efflux by elacridar in in vitro experiments significantly decreased fexofenadine efflux from hepatocytes, resulting in an increase in apparent fexofenadine uptake. The results from the present study clearly indicate that ABC transporter-mediated efflux in freshly isolated as well as cryopreserved rat and human hepatocytes should be taken into account in in vitro experiments used for modeling of drug metabolism and disposition.

A Modified Grapefruit Juice Eliminates Two Compound Classes as Major Mediators of the Grapefruit Juice–Fexofenadine Interaction: An In Vitro–In Vivo “Connect”

The grapefruit juice (GFJ)-fexofenadine interaction involves inhibition of intestinal organic anion transporting polypeptide (OATP)-mediated uptake. Only naringin has been shown clinically to inhibit intestinal OATP; other constituents have not been evaluated. The effects of a modified GFJ devoid of furanocoumarins (~99%) and polymethoxyflavones (~90%) on fexofenadine disposition were compared to effects of the original juice. Extracts of both juices inhibited estrone 3-sulfate and fexofenadine uptake by similar extents in OATP-transfected cells (~50% and ~25%, respectively). Healthy volunteers (n = 18) were administered fexofenadine (120 mg) with water, GFJ, or modified GFJ (240 mL) by randomized, three-way crossover design. Compared to water, both juices decreased fexofenadine geometric mean AUC and C(max) by ~25% (P ≤ .008 and P ≤ .011, respectively), with no effect on terminal half-life (P = .11). Similar effects by both juices on fexofenadine pharmacokinetics indicate furanocoumarins and polymethoxyflavones are not major mediators of the GFJ-fexofenadine interaction.

Enantioselective uptake of fexofenadine by Caco-2 cells as model intestinal epithelial cells

Fexofenadine contains a chiral carbon in its chemical structure and is orally administered as a racemic mixture. This study evaluated the selective uptake of fexofenadine enantiomers by Caco-2 cells as a model of intestinal epithelial cells. R(+)-fexofenadine or S(-)-fexofenadine was applied to Caco-2 cells, followed by incubation. After incubation, the amounts of fexofenadine enantiomers in cells were determined. The kinetic parameters for the uptake of fexofenadine enantiomers by Caco-2 cells were estimated using the Michaelis-Menten equation. The transporter-mediated uptake rate of R(+)-fexofenadine was 1.7-fold higher than that of S(-)-fexofenadine. The difference in transporter-mediated R(+)-fexofenadine and S(-)-fexofenadine uptake was completely diminished under ATP-depleted conditions and in the presence of organic anion transporter peptide (OATP) inhibitors. Also, a Dixon plot showed that each fexofenadine enantiomer was competitively inhibited by the other enantiomer. The ratio of R(+)-fexofenadine uptake to S(-)-fexofenadine uptake in the case of a racemic mixture was higher than that in the case of a single enantiomer. This study suggested that the selective absorption of fexofenadine enantiomers by intestinal epithelial cells might have been due to the selective uptake mediated by OATPs and that the difference in intestinal absorption was enhanced with a racemic mixture.

Vectorial Transport of Fexofenadine across Caco-2 Cells: Involvement of Apical Uptake and Basolateral Efflux Transporters

Fexofenadine is a nonsedative antihistamine that exhibits good oral bioavailability despite its zwitterionic chemical structure and efflux by P-gp. Evidence exists that multiple uptake and efflux transporters play a role in hepatic disposition of fexofenadine. However, the roles of specific transporters and their interrelationship in intestinal absorption of this drug are unclear. This study was designed to elucidate vectorial absorptive transport of fexofenadine across Caco-2 cells involving specific apical uptake and efflux transporters as well as basolateral efflux transporters. Studies with cellular models expressing single transporters showed that OATP2B1 expression stimulated uptake of fexofenadine at pH 6.0. Apical uptake of fexofenadine into Caco-2 cells was decreased by 45% by pretreatment with estrone 3-sulfate, an OATP inhibitor, at pH 6.0 but not at pH 7.4, indicating that OATP2B1 mediates apical uptake of fexofenadine into these cells. Examination of fexofenadine efflux from preloaded Caco-2 cells in the presence or absence of (i) the MRP inhibitor MK-571 and (ii) the P-gp inhibitor GW918 showed that apical efflux is predominantly mediated by P-gp, with a small contribution by MRP2, whereas basolateral efflux is predominantly mediated by MRP3. These results also showed that while OSTαβ is functionally active in the basolateral membrane of Caco-2 cells, it does not play a role in the export of fexofenadine. MK-571 decreased the absorptive transport of fexofenadine by 17%. However, the decrease in absorptive transport by MK-571 was 42% when P-gp was inhibited by GW918. The results provide a novel insight into a vectorial transport system mainly consisting of apical OATP2B1 and basolateral MRP3 that may play an important role in delivering hydrophilic anionic and zwitterionic drugs such as pravastatin and fexofenadine into systemic circulation upon oral administration.

The effects of the SLCO2B1 c.1457C&gt;T polymorphism and apple juice on the pharmacokinetics of fexofenadine and midazolam in humans

The objective was to determine the effects of the SLCO2B1 c.1457C> T polymorphism and apple juice on the pharmacokinetics of fexofenadine and midazolam in humans. Individuals were divided based on the genotype of SLCO2B1 c.1457C> T (n = 14, c.[1457C]+ c.[= ] 5,c.[1457C]+ c.[1457C> T] 5, and c.[1457C> T]+c.[1457C> T] 4). The oral pharmacokinetics of 60 mg fexofenadine and 5mg midazolam were assessed with water or apple juice (1200 ml/day) in a randomized crossover study. OATP2B1-mediated uptake of fexofenadine and midazolam was evaluated with Xenopus laevis oocyte gene-expression system. When fexofenadine was administered with water, subjects with c.[1457C> T] allele showed a significant decrease in fexofenadine in the area under the plasma concentration-time curve (AUC) compared with c.[1457C] + c[= ] subjects (1110 ± 347 vs. 1762 ± 542 ng . h/ml, P< 0.05). When administered with apple juice, a significant decrease in the fexofenadine AUC was observed compared with water (1342 ± 519 vs. 284 ± 79.2 ng . h/ml, P < 0.05). The apple juice induced decrease in fexofenadine AUC was significantly lower in subjects carrying the c.[1457C> T] allele. Neither the genotype nor the apple juice showed significant effects on the pharmacokinetics of midazolam except for a marginally significant decrease in Cmax after administration with apple juice. The uptake of fexofenadine by OATP2B1 cRNA-injected oocytes was significantly higher than that by water-injected oocytes. Apple juice, but not midazolam, significantly decreased the uptake of fexofenadine by OATP2B1 cRNA-injected oocytes. The results suggest that fexofenadine is a substrate of OATP2B1, and the transport function of OATP2B1 is subject to the genotype of SLCO2B1 c.1457C> T and apple juice. It is likely that apple juice has little effect on CYP3A.

Regional absorption of fexofenadine in rat intestine

Purpose Expression of Pgp along the GI-tract of rats increases towards distal segments. We assessed the in vivo relevance by determining the absorption of fexofenadine from proximal and distal parts of rat intestine. Since it has been reported that fexofenadine is also actively taken up by OATP/oatps, we quantified rat oatp1a5 and oatp2b1 mRNA in gut mucosa to elucidate a possible contribution of an oatp-mediated active uptake of fexofenadine. Methods Absorption was determined after drug administration into ligated segments of rat duodenum/upper jejunum and terminal ileum, respectively, in the absence and the presence of the Pgp blocker PSC-833s. Portal vein blood was sampled. Expression of Pgp in the mucosa of proximal and distal intestinal segments was analyzed by Western Blot. Oatp1a5 and oatp2b1 mRNA in intestinal mucosa was quantified by real-time qRT-PCR. Results Portal vein AUC 0–90 min of fexofenadine was significantly higher after absorption from proximal segments compared to distal segments. Accordingly, Pgp expression was significantly lower in proximal compared to distal segments. Inhibition of Pgp by PSC-833 affected fexofenadine absorption only in distal segments resulting in AUC values comparable to the proximal data. Both oatp1a5 and oatp2b1 mRNA expression increased along the small intestine. Conclusion The study demonstrates that Pgp is responsible for a limitation of fexofenadine absorption from distal small intestine. These findings are supported by the found pattern of expression for oatp1a5 and oatp2b1, showing that an active oatp-mediated uptake plays no role for fexofenadine absorption in rats.

Fexofenadine Brain Exposure and the Influence of Blood-Brain Barrier P-Glycoprotein After Fexofenadine and Terfenadine Administration

P-glycoprotein (P-gp) plays an important role in determining net brain uptake of fexofenadine. Initial in vivo experiments with 24-h subcutaneous osmotic minipump administration demonstrated that fexofenadine brain penetration was 48-fold higher in mdr1a(-/-) mice than in mdr1a(+/+) mice. In contrast, the P-gp efflux ratio at the blood-brain barrier (BBB) for fexofenadine was only approximately 4 using an in situ brain perfusion technique. Pharmacokinetic modeling based on the experimental results indicated that the apparent fexofenadine P-gp efflux ratio is time-dependent due to low passive permeability at the BBB. Fexofenadine brain penetration after terfenadine administration was approximately 25- to 27-fold higher than after fexofenadine administration in both mdr1a(+/+) and mdr1a(-/-) mice, consistent with terfenadine metabolism to fexofenadine in murine brain tissue. The fexofenadine formation rate after terfenadine in situ brain perfusion was comparable with that in a 2-h brain tissue homogenate in vitro incubation. The fexofenadine formation rate increased approximately 5-fold during a 2-h brain tissue homogenate incubation with hydroxyl-terfenadine, suggesting that the hydroxylation of terfenadine is the rate-limiting step in fexofenadine formation. Moreover, regional brain metabolism seems to be an important factor in terfenadine brain disposition and, consequently, fexofenadine brain exposure. Taken together, these results indicate that the fexofenadine BBB P-gp efflux ratio has been underestimated previously due to the lack of complete equilibration of fexofenadine across the blood-brain interface under typical experimental paradigms.

Investigation of the Inhibitory Effects of Various Drugs on the Hepatic Uptake of Fexofenadine in Humans

Fexofenadine (FEX), an H(1)-receptor antagonist, is eliminated from the liver mainly in an unchanged form. Our previous study suggested that organic anion-transporting polypeptide (OATP) 1B3 contributes mainly to the hepatic uptake of FEX. On the other hand, a clinical report demonstrated that a T521C mutation of OATP1B1 increased its plasma area under the plasma concentration-time curve. Several compounds are reported to have a drug interaction with FEX, and some of this may be caused by the inhibition of its hepatic uptake. We determined which transporters are involved in the hepatobiliary transport of FEX by using double transfectants and examined whether clinically reported drug interactions with FEX could be explained by the inhibition of its hepatic uptake. Vectorial basal-to-apical transport of FEX was observed in double transfectants expressing OATP1B1/multidrug resistance-associated protein 2 (MRP2) and OATP1B3/MRP2, suggesting that OATP1B1 as well as OATP1B3 is involved in the hepatic uptake of FEX and that MRP2 can recognize FEX as a substrate. The inhibitory effects of compounds on FEX uptake in OATP1B3-expressing HEK293 cells were investigated, and the maximal degree of increase in plasma AUC of FEX by drug interaction in clinical situations was estimated. As a result, cyclosporin A and rifampicin were found to have the potential to interact with OATP1B3-mediated uptake at clinical concentrations. From these results, most of the reported drug interaction cannot be explained by the inhibition of hepatic uptake of FEX, and different mechanisms such as the inhibition of intestinal efflux should be considered.

Intestinal Drug Transporter Expression and the Impact of Grapefruit Juice in Humans

The goals of this study were to assess the extent of human intestinal drug transporter expression, determine the subcellular localization of the drug uptake transporter OATP1A2, and then to assess the effect of grapefruit juice consumption on OATP1A2 expression relative to cytochrome P450 3A4 and MDR1. Expression of drug uptake and efflux transporters was assessed using human duodenal biopsy samples. Fexofenadine uptake by different transporters was measured in a transporter-transfected cell line. We investigated the influence of grapefruit juice on pharmacokinetics of orally administered fexofenadine. The effect of grapefruit juice on the expression of intestinal transporters was determined using real-time polymerase chain reaction and Western blot analysis. In the duodenum of healthy volunteers, an array of CYP enzymes as well as uptake and efflux transporters was expressed. Importantly, uptake transporters thought to be liver-specific, such as OATP1B1 and 1B3, as well as OATP2B1 and 1A2 were expressed in the intestine. However, among OATP transporters, only OATP1A2 was capable of fexofenadine uptake when assessed in vitro. OATP1A2 colocalized with MDR1 to the brush border domain of enterocytes. Consumption of grapefruit juice concomitantly or 2 h before fexofenadine administration was associated with reduced oral fexofenadine plasma exposure, whereas intestinal expression of either OATP1A2 or MDR1 remained unaffected. In conclusion, an array of drug uptake and efflux transporters are expressed in the human intestine. OATP1A2 is likely the key intestinal uptake transporter for fexofenadine absorption whose inhibition results in the grapefruit juice effect. Although short-term grapefruit juice ingestion was associated with reduced fexofenadine availability, OATP1A2 or MDR1 expression was unaffected.

INHIBITION OF OAT3-MEDIATED RENAL UPTAKE AS A MECHANISM FOR DRUG-DRUG INTERACTION BETWEEN FEXOFENADINE AND PROBENECID

Fexofenadine, a nonsedating antihistamine drug, is effective for the treatment of seasonal allergic rhinitis and chronic urticaria. Simultaneous administration of probenecid increases the plasma concentration of fexofenadine due to an inhibition of its renal elimination in healthy volunteers (Clin Pharmacol Ther 77:17-23, 2005). The purpose of the present study is to investigate the possibility that the drug-drug interaction between fexofenadine and probenecid involves the renal basolateral uptake process. The uptake of fexofenadine was determined in HEK293 cells expressing human organic anion transporter 1 (OAT1/SLC22A6), OAT2 (SLC22A7), OAT3 (SLC22A8), and organic cation transporter 2 (OCT2/SLC22A2). Only hOAT3-HEK showed a significantly greater accumulation of fexofenadine than that in vector-HEK, which was saturable with K(m) and V(max) values of 70.2 microM and 120 pmol/min/mg protein, respectively. Inhibition potency of probenecid for the uptake of fexofenadine was compared between hOAT3 and organic anion-transporting peptide 1B3 (hOATP1B3), a transporter responsible for the hepatic uptake of fexofenadine (Drug Metab Dispos 33:1477-1481, 2005). The K(i) values were determined to be 1.30 and 130 microM for hOAT3 and hOATP1B3, respectively, with Hill coefficients of 0.76 and 0.64, respectively. The K(i) value of probenecid for hOAT3, but not for hOATP1B3, was significantly lower than the maximum unbound plasma concentration of probenecid at clinical dosages. These results suggest that the renal drug-drug interaction between fexofenadine and probenecid is probably explained by an inhibition of the renal uptake of fexofenadine via hOAT3, at least in part.

PI-50OATP1A2 is the major uptake transporter of fexofenadine in humans

BACKGROUND/AIMS The antihistaminic drug fexofenadine is frequently used as an in vivo probe of P-glycoprotein transporter function in humans. We have previously shown that OATP1A2 (OATP-A) is able to mediate the cellular uptake of fexofenadine. In this study the role of other OATPs and polymorphisms in OATP1A2 to fexofenadine uptake was assessed. METHODS We expressed an array of drug uptake transporters, including wildtype and variant OATP1A2 in HeLa cells using a recombinant vaccinia system and determined fexofenadine cellular uptake. RESULTS OATP1A2, but not 1B1 (OATP-C), 1B3 (OATP8) or 2B1 (OATP-B), was capable of transporting fexofenadine in expressed HeLa cells. OATP1A2*3, *5, *6, and *7 revealed significantly lower transport activity compared to OATP1A2*1. Interestingly human OCT1 showed a low but detectable transport activity for fexofenadine. In contrast to humans, multiple rat Oatps, including rat Oatp1a1, 1a4, 1a5 and 1b2 were capable of fexofenadine transport. CONCLUSION Our results indicate that OATP1A2 may be an important determinant of fexofenadine disposition in humans. Furthermore, hepatic uptake of fexofenadine is likely mediated by OCT1 and not by OATP1B1 or 1B3. Since OATP1A2 is expressed in the intestine, kidney and brain, our findings suggest polymorphisms in OATP1A2 may contribute to intersubject variability in response to fexofenadine. Clinical Pharmacology & Therapeutics (2005) 79, P20–P20; doi: 10.1016/j.clpt.2005.12.071

Transporter-mediated Intestinal Absorption of Fexofenadine in Rats

Both influx and efflux transporters are thought to be involved in the intestinal absorption of fexofenadine. The present study examined the influx transporter-mediated intestinal absorption of fexofenadine in rats, focusing on the role of rat oatp3 (Oatp1a5). The intestinal permeability of fexofenadine was evaluated by means of the Ussing chamber method in the presence of a P-glycoprotein inhibitor to block efflux transport. The permeability of fexofenadine from the mucosal to the serosal side was higher than that from the serosal side to the mucosal side. Transport of fexofenadine was saturable, and was significantly decreased by an organic anion transporting polypeptide (oatp) inhibitor. Furthermore, uptake of fexofenadine by Xenopus oocytes expressing rat oatp3 was significantly greater than that by water-injected oocytes, and the affinity of oatp3 for fexofenadine (Km) was about 60 microM, which is comparable with the value obtained by the Ussing chamber method using rat intestinal tissues. These results indicate that oatp3 plays a role as an influx transporter in the intestinal absorption of fexofenadine in rats.

Fexofenadine pharmacokinetics are associated with a polymorphism of the SLCO1B1 gene (encoding OATP1B1)

Fexofenadine pharmacokinetics are associated with a polymorphism of the <i>SLCO1B1</i> gene (encoding OATP1B1)

Antibiotic treatment of suspected neonatal meningitis.

P-glycoprotein (P-gp) plays an important role in determining net brain uptake of fexofenadine. Initial in vivo experiments with 24-h subcutaneous osmotic minipump administration demonstrated that fexofenadine brain penetration was 48-fold higher in <i>mdr1a</i>(–/–) mice than in <i>mdr1a</i>(+/+) mice. In contrast, the P-gp efflux ratio at the blood-brain barrier (BBB) for fexofenadine was only ∼4 using an in situ brain perfusion technique. Pharmacokinetic modeling based on the experimental results indicated that the apparent fexofenadine P-gp efflux ratio is time-dependent due to low passive permeability at the BBB. Fexofenadine brain penetration after terfenadine administration was ∼25- to 27-fold higher than after fexofenadine administration in both <i>mdr1a</i>(+/+) and <i>mdr1a</i>(–/–) mice, consistent with terfenadine metabolism to fexofenadine in murine brain tissue. The fexofenadine formation rate after terfenadine in situ brain perfusion was comparable with that in a 2-h brain tissue homogenate in vitro incubation. The fexofenadine formation rate increased ∼5-fold during a 2-h brain tissue homogenate incubation with hydroxyl-terfenadine, suggesting that the hydroxylation of terfenadine is the rate-limiting step in fexofenadine formation. Moreover, regional brain metabolism seems to be an important factor in terfenadine brain disposition and, consequently, fexofenadine brain exposure. Taken together, these results indicate that the fexofenadine BBB P-gp efflux ratio has been underestimated previously due to the lack of complete equilibration of fexofenadine across the blood-brain interface under typical experimental paradigms.