Use of uptake intrinsic clearance from attached rat hepatocytes to predict hepatic clearance for poorly permeable compounds

1. We previously reported that the accuracy of clearance (CL) prediction could be differentiated by permeability. CL was drastically under-predicted by in vitro metabolic intrinsic clearance (CL_int) for compounds with low permeability (<5?×?10^?6 cm/s).

2. We determined apparent uptake CL_int by measuring initial disappearance from medium using attached rat hepatocytes and metabolic CL_int by measuring parent depletion in suspended rat hepatocytes (cells and medium).

3. Uptake and metabolic CL_int were comparable for highly permeable metabolic marker compounds. In contrast, uptake CL_int was 3- to 40-fold higher than metabolic CL_int for rosuvastatin, bosentan, and 15 proprietary compounds, which had low permeability, suggesting that uptake could be a rate-determining step in hepatic elimination for these poorly permeable compounds.

4. The prediction of hepatic CL was improved significantly when using uptake CL_int for the compounds with low permeability. The average fold error was 2.2 and 6, as opposed to >11 and >47 by metabolic CL_int, with and without applying a scaling factor of 4, respectively.

5. Uptake CL_int from attached hepatocytes can be used as an alternative approach to predict hepatic clearance and to understand the significance of hepatic uptake in elimination in an early drug discovery setting.

     

Comparison of intrinsic metabolic clearance in fresh and cryopreserved human hepatocytes

1. We compared the intrinsic clearance (CL_int) of a number of substrates in suspensions of fresh and cryopreserved human hepatocytes from seven donors.

2. CL_int values for a cocktail incubation of phenacetin, diclofenac, diazepam, bufuralol, midazolam, and hydroxycoumarin were 4.9?±?3.4, 18?±?7.2, 5.1?±?4.9, 6.3?±?3.3, 9.8?±?5.8 and 22?±?14?μl min^?1/10⁶ cells, respectively, and they correlated well with corresponding CL_int values using cryopreserved hepatocytes from 25 different donors.

3. CL_int values of each cocktail substrate and 20 AstraZeneca new chemical entities were compared in fresh and cryopreserved hepatocytes from the same three donors. There was a statistically significant correlation between CL_int in fresh and cryopreserved hepatocytes for each of the three livers (p?int values was 1.03.

4. In conclusion, the results add further support to the use of cryopreserved human hepatocytes as a screening model for the intrinsic clearance of new chemical entities.

     

In vitro-in vivo correlation for intrinsic clearance for CP-409,092 and sumatriptan: a case study to predict the in vivo clearance for compounds metabolized by monoamine oxidase

Oxidative deamination of the GABA(A) partial agonist CP-409,092 and sumatriptan represents a major metabolic pathway and seems to play an important role for the clearance of these two compounds. Similar to sumatriptan, human mitochondrial incubations with deprenyl and clorgyline, probe inhibitors of monoamine oxidase B and monoamine oxidase A (MAO-B and MAO-A), respectively, showed that CP-409,092 was metabolized to a large extent by the enzyme MAO-A. The metabolism of CP-409,092 and sumatriptan was therefore studied in human liver mitochondria and in vitro intrinsic clearance (CL(int)) values were determined and compared to the corresponding in vivo oral clearance (CL(PO)) values. The overall objective was to determine whether an in vitro-in vivo correlation (IVIVC) could be described for compounds cleared by MAO-A. The intrinsic clearance, CL(int), of CP-409,092 was approximately 4-fold greater than that of sumatriptan (CL(int), values were calculated as 0.008 and 0.002 ml/mg/min for CP-409,092 and sumatriptan, respectively). A similar correlation was observed from the in vivo metabolic data where the unbound oral clearance, CL(u)(PO), values in humans were calculated as 724 and 178 ml/min/kg for CP-409,092 and sumatriptan, respectively. The present work demonstrates that it is possible to predict in vivo metabolic clearance from in vitro metabolic data for drugs metabolized by the enzyme monoamine oxidase.     

Sources of interindividual variability in IVIVE of clearance: an investigation into the prediction of benzodiazepine clearance using a mechanistic population-based pharmacokinetic model

1. Prediction of metabolic clearance in extreme individuals rather than the ‘average human’ is becoming an attractive tool within the pharmaceutical industry.

2. The current study involved prediction of variability in metabolic clearance for alprazolam, triazolam and midazolam with emphasis on the following factors: first, evaluation of clearance prediction accuracy using intrinsic clearance (CL_int) data from in vitro metabolic data and back-calculation from in vivo clearance data. Second, the sensitivity of predicted in vivo variability to changes in variability for physiological parameters (e.g. liver weight, haematocrit, CYP3A abundance). Finally, reported estimates of variability in hepatic CYP3A4 abundance (coefficient of variation (CV) 95%) were refined by separating experimental from interindividual variability using a repeat measurement protocol in 52 human liver samples.

3. Using in vitro metabolic data, predicted clearances were within 2-fold of observed for triazolam and midazolam. Clearance of alprazolam was overpredicted by 2.0- to 3.7-fold. Use of in vivo CL_int values improved prediction of intravenous clearance to within 2-fold of observed for all drugs.

4. Initially, the variability in clearance was overestimated for all drugs (by 1.8- to 3.6-fold). Use of a reduced hepatic CYP3A4 CV of 41%, representative of interindividual variability alone improved predictions of variability in clearance for all drugs to within 2-fold of observed.

     

Metabolism,pharmacokinetics and excretion of the GABAA receptor partial agonist [14C]CP-409,092 in rats

1. The metabolism and excretion of a GABA_A partial agonist developed for the treatment of anxiety, CP-409,092; 4-oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxylic acid (4-methylaminomethyl-phenyl)-amide, were studied in rats following intravenous and oral administration of a single doses of [¹⁴C]CP-409,092.

2. The pharmacokinetics of CP-409,092 following single intravenous and oral doses of 4 and 15?mg kg^?1, respectively, were characterized by high clearance of 169?±?18?ml min^?1 kg^?1, a volume of distribution of 8.99?±?1.46 l kg^?1, and an oral bioavailability of 2.9% ± 3%.

3. Following oral administration of 100?mg kg^?1 [¹⁴C]CP-409,092, the total recovery was 89.1% ± 3.2% for male rats and 89.3% ± 0.58% for female rats. Approximately 87% of the radioactivity recovered in urine and faeces were excreted in the first 48?h. A substantial portion of the radioactivity was measured in the faeces as unchanged drug, suggesting poor absorption and/or biliary excretion. There were no significant gender-related quantitative/qualitative differences in the excretion of metabolites in urine or faeces.

4. The major metabolic pathways of CP-409,092 were hydroxylation(s) at the oxo-tetrahydro-indole moiety and oxidative deamination to form an aldehyde intermediate and subsequent oxidation to form the benzoic acid. The minor metabolic pathways included N-demethylation and subsequent N-acetylation and oxidation.

5. The present work demonstrates that oxidative deamination at the benzylic amine of CP-409,092 and subsequent oxidation to form the acid metabolite seem to play an important role in the metabolism of the drug, and they contribute to its oral clearance and low exposure.

     

Sex differences in pharmacokinetics of cilostazol in rats

1. The pharmacokinetics of cilostazol was investigated after oral and intravenous administration in both male and female rats. After oral administration, area under serum concentration–time curve (AUC) was about 35-fold higher in female rats than in male rats, and absolute bioavailability was about 5.8-fold higher in female rats than in male rats.

2. Total body clearance (CL_total) for female rats was around one-sixth of that for male rats. In vivo hepatic clearance (CL_h) calculated based on isolated liver perfusion studies was even higher than or around 90% of the in vivo CL_total of cilostazol for female and male rats, respectively, indicating that cilostazol is mainly eliminated by the liver in both male and female rats.

3. In vitro metabolism studies utilizing hepatic microsomes and recombinant cytochrome (CYP) isoforms clearly indicated that major metabolites of cilostazol were generated extensively with hepatic microsomes of male rats and that male-predominant CYP3A2 and male-specific CYP2C11 were mainly responsible for the hepatic metabolism of cilostazol. Therefore, the great sex differences in the pharmacokinetics of cilostazol were mainly attributed to the large difference in hepatic metabolism.

4. Our experimental results also suggested that the substantial metabolism of cilostazol in the small intestine and its possible saturation would be responsible for dose-dependent bioavailability in both male and female rats.

     

Decreased urinary secretion of belotecan in folic acid-induced acute renal failure rats due to down-regulation of Oat1 and Bcrp

1. The effects of folic acid-induced acute renal failure on the renal excretion of belotecan were investigated in rats after intravenous administration.

2. Both glomeruli and renal tubules were seriously damaged by folic acid-induced acute renal failure. The renal excretion clearance, CL_r, of belotecan was significantly decreased by folic acid-induced acute renal failure. Furthermore, glomerular filtration rate and secretion clearance of the drug were dramatically decreased by folic acid-induced acute renal failure.

3. In vivo renal uptake of belotecan was inhibited by p-aminohippurate, whereas renal excretion was inhibited by GF120918, but not by verapamil and bromosulphalein. This indicates that Oat1/3 and Bcrp are involved in the renal uptake and urinary excretion of belotecan, respectively.

4. Both mRNA and protein levels of Oat1, Oat3 and Bcrp were significantly decreased in folic acid-induced acute renal failure rats. Based on the finding that belotecan is a substrate of OAT1 but not of OAT3, the decrease in CL_r of belotecan in folic acid-induced acute renal failure could, therefore, mainly be attributed to the down-regulation of Oat1 and Bcrp, in addition to the decrease in glomerular filtration rate.

     

Stereoselective degradation of metalaxyl and its enantiomers in rat and rabbit hepatic microsomes in vitro

1. The stereoselective degradations of racemate metalaxyl (rac-MX) and its single enantiomers in rat and rabbit hepatic microsomes were assayed by a chiral high-performance liquid chromatography method.

2. The t_1/2 of (+)-S-MX in rat liver microsomes was between 7–8?min tested by rac-MX and the individual (+)-S-enantiomer, respectively, and that for (?)-R-MX was 15–16?min. In contrast, t_1/2 in rabbit liver microsomes was much longer and showed great difference when using racemate and single enantiomer, which was similar to the results of in vivo study.

3. The enantioselectivity in rat hepatic microsomes was more evident and the degradations of MX enantiomers in rat and rabbit hepatic microsomes were Nicotinamide adenine dinucleotide phosphate-dependent.

4. Michaelis constant (K_m) and intrinsic metabolic clearance (CL_int) of (+)-S-MX were larger than that of (?)-R-MX and there was no chiral inversion from (+)-S-MX to (?)-R-MX or vice versa in both rat and rabbit hepatic microsomes.

     

Use of primary rat hepatocytes in the gel entrapment culture to predict in vivo biliary excretion

1. In vitro models have been widely used in characterizing the hepatobiliary elimination of compounds. However, the application of in vitro models is often limited by their imperfect simulation of in vivo situations. The current paper aims to introduce the gel entrapment culture of rat hepatocytes as an alternative method for measuring hepatobiliary transport, with the sandwich culture of rat hepatocytes set as the control.

2. First, the culture conditions of the gel-entrapped hepatocytes were modified to enhance hepatic transport function. When cultured under optimal conditions, i.e. the collagen concentration was set to 0.6?mg/mL and the regular Williams’ E medium was supplemented with epidermal growth factor, the hepatocytes maintained much higher hepatic transporter gene expression levels and transport activities than that in regular gel entrapment and sandwich culture.

3. Compared with the actual values in rats, the predicted intrinsic biliary clearance (CL_{bile,int,predicted}) of the 10 model compounds in the optimized gel entrapment culture showed a high correlation coefficient squared (R²) of 0.94, with the majority falling within the two-fold error range of the in vivo values, which was much better than the comparable sandwich culture.

4. All of these results indicate that the optimized gel entrapment culture of hepatocytes is a suitable approach for estimating in vivo biliary excretion.

     

Effects of Escherichia coli lipopolysaccharide on the metformin pharmacokinetics in rats

1. The time-dependent (2-h, 24-h, and 96-h) effects of Escherichia coli lipopolysaccharide (ECLPS) on the intravenous (100?mg kg^?1) and oral (100?mg kg^?1) metformin pharmacokinetics were evaluated in rats.

2. After the intravenous administration of metformin to 24-h and 96-h ECLPS rats, the total area under the plasma concentration–time curve from time zero to time infinity (AUCs) and time-averaged non-renal clearances (CL_NRs) of metformin were significantly greater and slower, respectively, than the controls. However, after the oral administration of metformin, the AUCs of metformin were comparable among four groups of rats.

3. The greater (slower) intravenous AUCs (CL_NRs) of metformin in 24-h and 96-h ECLPS rats were due to the slower hepatic intrinsic clearance (CL_int) because of a decrease in the protein expression of hepatic cytochrome P450 (CYP) 2C11 and/or CYP3A subfamily than controls. The comparable oral AUCs among four groups of rats were mainly due to the comparable gastrointestinal metabolism (CL_int).

     

Practical use of the regression offset approach for the prediction of in vivo intrinsic clearance from hepatocytes

1. Systematic under-prediction of clearance is frequently associated with in vitro kinetic data when extrapolated using physiological scaling factors, appropriate binding parameters and the well-stirred model. The present study describes a method of removing this systematic bias through application of empirical correction factors derived from regression analyses applied to the in vitro and in vivo data for a defined set of reference compounds.

2. Linear regression lines were established with in vivo intrinsic clearance (CLint), derived from in vivo clearance data and scaled in vitro intrinsic clearance from isolated hepatocyte incubations. The scaled CLint was empirically corrected to a predicted in vivo CLint using the slope and intercept from a uniform weighted linear regression applied to the in vitro to in vivo extrapolation.

3. Cross validation of human data demonstrated that 66% of the reference compounds had a predicted in vivo CLint within two-fold of the observed value. The average absolute fold error (AAFE) for the in vivo CLint predictions was 1.90. For rat, 54% of the compounds had a predicted value within two-fold of the observed and the AAFE was 1.98.

4. Three AstraZeneca projects are used to exemplify how a two-sided prediction interval, applied to the rat regression corrected reference data, can form the basis for assessing the likelihood that, for a given chemical series, the in vitro kinetic data is predictive of in vivo clearance and is therefore appropriate to guide optimisation of compound metabolic stability.

     

In vivo hepatic clearance of lipophilic drugs predicted by in vitro uptake data into cryopreserved hepatocytes suspended in sera of rats,guinea pigs,monkeys and humans

1. Evaluation of uptake of lipophilic acid compounds into hepatocytes was an unresolved drug development issue because of their adsorption to cells and materials and low analytical sensitivity and accuracy in assessment of protein bindings.

2. Uptake assays of compounds using hepatocytes suspended in serum were expected to solve these problems for prediction of in vivo hepatic clearance. Here, for compounds with high protein binding (>99%), diflunisal, montelukast, cerivastatin, telmisartan, fluvastatin and six new drug candidates, in vivo hepatic clearance predicted based on hepatic depletion and uptake (CL_{h, uptake, predicted}) data using hepatocytes in the absence and presence of sera was investigated.

3. In vitro hepatic uptake results with hepatocytes suspended in serum improved prediction of human hepatic clearance values for highly lipophilic montelukast and telmisartan. In vivo CL_{h, uptake, predicted} values of six new highly lipophilic acid drug candidates (protein binding >99.97%) and diflunisal, montelukast and cerivastatin predicted based on hepatocytes suspended in serum were within threefold differences of their total clearance in vivo in rats, guinea pigs or monkeys, except for montelukast in monkeys (5.8-fold).

4. These results suggest that the human hepatic uptake in hepatocytes suspended in serum is useful for prediction of CL_{h, uptake, predicted}, especially for highly lipophilic/protein binding acid compounds.

     

Prediction of animal clearance using naïve Bayesian classification and extended connectivity fingerprints

1. In silico models were developed for predicting high animal clearance using naïve Bayesian classification and extended connectivity fingerprints. Validation and test sets were created from a structurally diverse database of mouse, rat, dog, and monkey clearance (CL) representing approximately 20 000 unique compounds. Model performance was compared with experimental predictors used widely in drug discovery, namely in vitro intrinsic clearance (CL_i) and CL from a lower preclinical species.

2. The Bayesian model for dog CL was a better predictor than experimental rat or mouse CL. The Bayesian model for rat CL performed at least as well as mouse CL. Bayesian models outperformed mouse, rat, and monkey CL_i for predicting mouse, rat, and monkey CL, respectively.

3. These models can be used to optimize chemical libraries, direct new chemical synthesis and increase efficiency of screening cascades for lead optimization while reducing overall drug discovery cost, time and animal usage.

     

Understanding the clinical pharmacokinetics of a GABAA partial agonist by application of in vitro tools

1. 4-Oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxylic acid (4-methylaminomethyl-phenyl)-amide (1), developed for general anxiety disorder, was discontinued from clinical development due to unsuitable oral pharmacokinetics.

2. In humans, (1) demonstrated an unacceptable high apparent oral clearance (Cl_p/F) that also demonstrated a supraproportional dose-exposure relationship. Secondary peaks in the plasma concentration-time profile suggested possible enterohepatic recirculation of (1). A combination of in vitro mechanistic tools was applied to better understand the processes underlying these complex clinical pharmacokinetic profiles of (1).

3. In metabolism experiments, (1) was shown to be a substrate of monoamine oxidase A (MAO-A) as well as being metabolized by cytochrome P450. The former appeared to be a high K_M process with a high capacity, while the latter showed saturation between 1 and 10 μM, consistent with the supraproportional dose-exposure relationship.

4. In a sandwich-cultured hepatocyte model, (1) was shown to be a substrate for both uptake and efflux into the canicular space, which is consistent with the observation of pharmacokinetics suggestive of enterohepatic recirculation. Finally, in human epithelial colon adenocarcinoma cell line (Caco-2) and Madin-Darby canine kidney cells transwell flux experiments, (1) was shown to have relatively low permeability and a basolateral-to-apical flux ratio consistent with the activity of P-glycoprotein.

5. In combination, a compounding of the contributions of MAO-A, hepatic uptake and efflux transporters, and P-glycoprotein to the disposition of (1) may underlie the low oral exposure, saturable clearance, and aberrant concentration versus time profiles observed for this compound in humans.

     

Prediction of differences in in vivo oral clearance of N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]ethylamine monohydrochloride (NE-100) between extensive and poor metabolizers from in vitro metabolic data in human liver microsomes lacking CYP2D6 activity and recombinant CYPs

1. It has previously been reported that N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100) was predominantly metabolized by cytochrome P450 (CYP) 2D6 in human liver microsomes (HLM). In the present study, the contribution of CYP forms involved in the formation of the major metabolites of NE-100 in human liver lacking CYP2D6 activity (PM-HLM) has been predicted by use of in vitro kinetic data on recombinant CYPs microsomes (rCYPs).

2. In PM-HLM, NE-100 is predicted to be metabolized to N-despropyl-NE-100 (NE-098), p-hydroxy-NE-100 (NE-152) and m-hydroxyl-NE-100 (NE-163), but not to O-demethy-NE-100 (NE-125), which is a major metabolite in pooled human liver microsomes (EM-HLM). The relative activity factor approach assumed that NE-098 formation is predominantly catalysed by CYP3A4 and CYP2C9 and the NE-152?+?163mix (a mixture of two hydroxylated metabolites, NE-152 and NE-163) formation is only catalysed by CYP3A4.

3. The predicted contribution rates of CYP3A4 and CYP2C9 for NE-098 formation were 58.1 and 34.6%, respectively, in PM-HLM. These predicted results were strongly supported by kinetic and inhibition studies using PM-HLM. The intrinsic clearance of NE-100 predicted from rCYPs (the predicted CL_{int-HLM-total}) corresponded to those observed from EM- and PM-HLM (the observed CL_int-HLM).

4. The in vivo oral clearance (CL_oral) of NE-100 in extensive metabolizers and poor metabolizers of CYP2D6 was predicted to be 50?times higher in extensive metabolizers than poor metabolizers using in vitro–in vivo scaling method based on the dispersion model. These data suggest that polymorphism of CYP2D6 might greatly affect NE-100 metabolism in vivo.

     

The evolution of the OATP hepatic uptake transport protein family in DMPK sciences: from obscure liver transporters to key determinants of hepatobiliary clearance

1. Over the last two decades the impact on drug pharmacokinetics of the organic anion transporting polypeptides (OATPs: OATP-1B1, 1B3 and 2B1), expressed on the sinusoidal membrane of the hepatocyte, has been increasingly recognized.

2. OATP-mediated uptake into the hepatocyte coupled with subsequent excretion into bile via efflux proteins, such as MRP2, is often referred to as hepatobiliary excretion.

3. OATP transporter proteins can impact some drugs in several ways including pharmacokinetic variability, pharmacodynamic response and drug-drug interactions (DDIs).

4. The impact of transporter mediated hepatic clearance is illustrated with case examples, from the literature and also from the Pfizer portfolio.

5. The currently available in vitro techniques to study the hepatic transporter proteins involved in the hepatobiliary clearance of drugs are reviewed herein along with recent advances in using these in vitro data to predict the human clearance of compounds recognized by hepatic uptake transporters.

     

Determination of drug-metabolizing enzyme activity in vivo : pharmacokinetic and statistical issues

1. Chlorpyrifos (CPF), an organophosphorus (OP) pesticide, is bioactivated by cytochrome P450s (CYPs) to the active metabolite chlorpyrifos oxon (CPF-O). Given that human CYP2B6 has the highest intrinsic clearance (CL_int) for CPF bioactivation, CYP2B6 polymorphisms may impact human susceptibility to CPF at real world environmental and occupational CPF exposure levels.

2. CYP2B6.4,.5,.7, and .18 were over-expressed in mammalian COS-1 cells to assess the impact of CYP2B6 variants on the K_m and V_max for bioactivation of CPF. Cell lysates were incubated with CPF (0–100 μM) and the production of CPF-O was measured via HPLC analysis. CYP2B6 content was determined by western blot.

3. CYP2B6.18 had neither detectable protein nor activity levels. The V_max value for each remaining variant was significantly higher than wild-type (CYP2B6.1, V_max 4.13?×?10⁴ pmol/min/nmol CYP2B6), with CYP2B6.4,.5, and .7 having V_max values of 4.52?×?10⁵, 1.82?×?10⁵, and 9.60?×?10⁴ pmol/min/nmol CYP2B6, respectively. The K_m values for these variants ranged from 0.39 to 1.09 μM and were not significantly different from wild-type. All active variants examined had significantly higher CL_int than CYP2B6.1.

4. Variants of CYP2B6 have altered capacity to bioactivate CPF and may affect individual susceptibility by altering the V_max for CPF-O formation.

     

Pharmacokinetics of mirodenafil and its two metabolites,SK3541 and SK3544, after intravenous and oral administration of mirodenafil to streptozotocin-induced diabetes mellitus rats

1. The area under the curve (AUC) of mirodenafil after intravenous administration in diabetes mellitus induced by streptozotocin (DMIS) rats was significantly smaller (by 28.0?%) than the control value, and the AUC_SK3541/AUC_mirodenafil ratio was significantly greater (by 130?%) in DMIS rats. This may be explained by the significantly faster hepatic CL_int of mirodenafil, owing to increased hepatic CYP1A, CYP2B1/2, CYP2D, and CYP3A expression, and a faster hepatic blood flow rate, compared with control values.

2. The AUC of mirodenafil after oral administration was comparable between DMIS and control rats, possibly because of the comparable intestinal CL_int, which may be attributable to increased CYP1A2 expression and decreased CYP2D expression in the intestines of DMIS rats.

     

Interspecies scaling and prediction of human clearance: comparison of small- and macro-molecule drugs

1. Human clearance prediction for small- and macro-molecule drugs was evaluated and compared using various scaling methods and statistical analysis.

2. Human clearance is generally well predicted using single or multiple species simple allometry for macro- and small-molecule drugs excreted renally.

3. The prediction error is higher for hepatically eliminated small-molecules using single or multiple species simple allometry scaling, and it appears that the prediction error is mainly associated with drugs with low hepatic extraction ratio (Eh). The error in human clearance prediction for hepatically eliminated small-molecules was reduced using scaling methods with a correction of maximum life span (MLP) or brain weight (BRW).

4. Human clearance of both small- and macro-molecule drugs is well predicted using the monkey liver blood flow method. Predictions using liver blood flow from other species did not work as well, especially for the small-molecule drugs.

     

Pharmacokinetics of fexofenadine following LPS administration to rats

1. The function and expression of drug transporters, including P-glycoprotein (P-gp) and organic-anion transporting polypeptides (Oatps), have been investigated but it is not well established how variables such as disease processes affect them. Fexofenadine is a substrate of these transporters and it was previously shown that its clearance is reduced in the rat isolated perfused liver following treatment with E.coli lipopolysaccharide (LPS). However, whether this translates to altered fexofenadine pharmacokinetics in vivo is yet to be established.

2. E.coli LPS at 5?mg/kg or sterile saline (control) was injected intraperitoneally in rats. Oral or intravenous (IV) fexofenadine (10?mg/kg) was administered 24?h later and plasma and urine samples collected for pharmacokinetic analysis.

3. LPS treatment did not significantly change the pharmacokinetics of IV fexofenadine, although there was a good correlation between weight loss and clearance suggesting reduced clearance in more severely affected animals. However, AUC_0–∞ of oral fexofenadine was a significantly higher in LPS-treated animals (13.9?±?9.76 min·µg/ml) compared to controls (5.53?±?1.12 min·µg/ml).

4. In conclusion, LPS treatment increased the bioavailability of fexofenadine but did not affect other pharmacokinetic parameters. This is consistent with a reduction in hepatic Oatp and/or P-gp for a high extraction ratio drug such as fexofenadine.