The Pharmacokinetics and Hepatic Disposition of Repaglinide in Pigs: Mechanistic Modeling of Metabolism and Transport

The predictive power of using in vitro systems in combination with physiologically based pharmacokinetic (PBPK) modeling to elucidate the relative importance of metabolism and carrier-mediated transport for the pharmacokinetics was evaluated using repaglinide as a model compound and pig as the test system. Repaglinide was chosen as model drug as previous studies in humans have shown that repaglinide is subject to both carrier-mediated influx to the liver cells and extensive hepatic metabolism. A multiple sampling site model in pig was chosen since it provides detailed in vivo information about the liver disposition. The underlying assumption was that both metabolism and carrier-mediated transport are also important for the hepatic disposition of repaglinide in pigs. Microsomes and primary hepatocytes were used for in vitro evaluation of enzyme kinetics and cellular disposition, respectively. In vitro data were generated both with and without metabolism inhibitors (ketoconazole, bezafibrate and trimethoprim) and transport inhibitors (diclofenac and quinine) providing input into a semi-PBPK model. In vivo data were also generated with and without the same enzyme and transporter inhibitors, alone and in combination. The pigs were given repaglinide as intravenous infusions with and without inhibitors in a sequential manner, i.e., a control phase and a test phase. Parameters describing the passive and carrier-mediated flux as well as metabolism were estimated in the control phase. The result from test phase was used to gain further knowledge of the findings from the control phase. The in vivo pig model enabled simultaneous sampling from plasma (pre- and postliver and peripheral) as well as from bile and urine. A semi-PBPK model consisting of 11 compartments (6 tissues + 5 sampling sites) was constructed for the mechanistic elucidation of the liver disposition, in vitro based in vivo predictions, sensitivity analyses and estimations of individual pharmacokinetic parameters. Both in vitro and in vivo results showed that carrier-mediated influx was important for the liver disposition. The in vivo findings were supported by the result from the test phase where hepatic clearance (4.3 mL min^–1 kg^–1) was decreased by 29% (metabolism inhibition), 43% (transport inhibition) and 57% (metabolism + transport inhibition). These effects were in good agreement with predicted levels. This study suggests that both metabolism and carrier-mediated uptake are of significant importance for the liver disposition of repaglinide in pigs

Human <i>in Vivo</i> Regional Intestinal Permeability: Quantitation Using Site-Specific Drug Absorption Data

Application of information on regional intestinal permeability has been identified as a key aspect of successful pharmaceutical product development. This study presents the results and evaluation of an approach for the indirect estimation of site-specific <i>in vivo</i> intestinal effective permeability (<i>P</i>_eff) in humans. Plasma concentration–time profiles from 15 clinical studies that administered drug solutions to specific intestinal regions were collected and analyzed. The intestinal absorption rate for each drug was acquired by deconvolution, using historical intravenous data as reference, and used with the intestinal surface area and the dose remaining in the lumen to estimate the <i>P</i>_eff. Forty-three new <i>P</i>_eff values were estimated (15 from the proximal small intestine, 11 from the distal small intestine, and 17 from the large intestine) for 14 active pharmaceutical ingredients representing a wide range of biopharmaceutical properties. A good correlation (<i>r</i>² = 0.96, slope = 1.24, intercept = 0.030) was established between these indirect jejunal <i>P</i>_eff estimates and jejunal <i>P</i>_eff measurements determined directly using the single-pass perfusion double balloon technique. On average, <i>P</i>_eff estimates from the distal small intestine and large intestine were 90% and 40%, respectively, of those from the proximal small intestine. These results support the use of the evaluated deconvolution method for indirectly estimating regional intestinal <i>P</i>_eff in humans. This study presents the first comprehensive data set of estimated human regional intestinal permeability values for a range of drugs. These biopharmaceutical data can be used to improve the accuracy of gastrointestinal absorption predictions used in drug development decision-making

A Model-Based Approach To Assessing the Importance of Intracellular Binding Sites in Doxorubicin Disposition

Doxorubicin is an anticancer agent, which binds reversibly to topoisomerase I and II, intercalates to DNA base pairs, and generates free radicals. Doxorubicin has a high tissue:plasma partition coefficient and high intracellular binding to the nucleus and other subcellular compartments. The metabolite doxorubicinol has an extensive tissue distribution. This porcine study investigated whether the traditional implementation of tissue binding, described by the tissue:plasma partition coefficient (<i>K</i>_p,t), could be used to appropriately analyze and/or simulate tissue doxorubicin and doxorubicinol concentrations in healthy pigs, when applying a physiologically based pharmacokinetic (PBPK) model approach, or whether intracellular binding is required in the semi-PBPK model. Two semi-PBPK models were developed and evaluated using doxorubicin and doxorubicinol concentrations in healthy pig blood, bile, and urine and kidney and liver tissues. In the generic semi-PBPK model, tissue binding was described using the conventional <i>K</i>_p,t approach. In the binding-specific semi-PBPK model, tissue binding was described using intracellular binding sites. The best semi-PBPK model was validated against a second data set of healthy pig blood and bile concentrations. Both models could be used for analysis and simulations of biliary and urinary excretion of doxorubicin and doxorubicinol and plasma doxorubicinol concentrations in pigs, but the binding-specific model was better at describing plasma doxorubicin concentrations. Porcine tissue concentrations were 400- to 1250-fold better captured by the binding-specific model. This model adequately predicted plasma doxorubicin concentration–time and biliary doxorubicin excretion profiles against the validation data set. The semi-PBPK models applied were similarly effective for analysis of plasma concentrations and biliary and urinary excretion of doxorubicin and doxorubicinol in healthy pigs. Inclusion of intracellular binding in the doxorubicin semi-PBPK models was important to accurately describe tissue concentrations during in vivo conditions

Effect on the Gastrointestinal Absorption of Drugs from Different Classes in the Biopharmaceutics Classification System, When Treating with Liraglutide

Like other GLP-1 receptor agonists used for treatment of type 2 diabetes, liraglutide delays gastric emptying. In this clinical absorption study, the primary objective was to investigate the effect of liraglutide (at steady state) on the rate and/or extent of gastrointestinal (GI) absorption of concomitantly orally taken drugs from three classes of the Biopharmaceutics Classification System (BCS). To provide a general prediction on liraglutide drug–drug absorption interaction, single-dose pharmacokinetics of drugs representing BCS classes II (low solubility–high permeability; atorvastatin 40 mg and griseofulvin 500 mg), III (high solubility–low permeability; lisinopril 20 mg), and IV (low solubility–low permeability; digoxin 1 mg) were studied in healthy subjects at steady state of liraglutide 1.8 mg, or placebo, in a two-period crossover design. With liraglutide, the oral drugs atorvastatin, lisinopril, and digoxin showed delayed <i>t</i>_max (by ≤2 h) and did not meet the criterion for bioequivalence for <i>C</i>_max (reduced <i>C</i>_max by 27–38%); griseofulvin had similar <i>t</i>_max and 37% increased <i>C</i>_max. Although the prespecified bioequivalence criterion was not met by all drugs, the overall plasma exposure (AUC) of griseofulvin, atorvastatin, lisinopril, and digoxin only exhibited minor changes and was not considered to be of clinical relevance

Combined in Vitro–in Vivo Approach To Assess the Hepatobiliary Disposition of a Novel Oral Thrombin Inhibitor

Two clinical trials and a large set of in vitro transporter experiments were performed to investigate if the hepatobiliary disposition of the direct thrombin inhibitor prodrug AZD0837 is the mechanism for the drug–drug interaction with ketoconazole observed in a previous clinical study. In Study 1, [³H]­AZD0837 was administered to healthy male volunteers (<i>n</i> = 8) to quantify and identify the metabolites excreted in bile. Bile was sampled directly from the jejunum by duodenal aspiration via an oro-enteric tube. In Study 2, the effect of ketoconazole on the plasma and bile pharmacokinetics of AZD0837, the intermediate metabolite (AR-H069927), and the active form (AR-H067637) was investigated (<i>n</i> = 17). Co-administration with ketoconazole elevated the plasma exposure to AZD0837 and the active form approximately 2-fold compared to placebo, which may be explained by inhibited CYP3A4 metabolism and reduced biliary clearance, respectively. High concentrations of the active form was measured in bile with a bile-to-plasma AUC ratio of approximately 75, indicating involvement of transporter-mediated excretion of the compound. AZD0837 and its metabolites were further investigated as substrates of hepatic uptake and efflux transporters in vitro. Studies in MDCK-MDR1 cell monolayers and P-glycoprotein (P-gp) expressing membrane vesicles identified AZD0837, the intermediate, and the active form as substrates of P-gp. The active form was also identified as a substrate of the multidrug and toxin extrusion 1 (MATE1) transporter and the organic cation transporter 1 (OCT1), in HEK cells transfected with the respective transporter. Ketoconazole was shown to inhibit all of these three transporters; in particular, inhibition of P-gp and MATE1 occurred in a clinically relevant concentration range. In conclusion, the hepatobiliary transport pathways of AZD0837 and its metabolites were identified in vitro and in vivo. Inhibition of the canalicular transporters P-gp and MATE1 may lead to enhanced plasma exposure to the active form, which could, at least in part, explain the clinical interaction with ketoconazole