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1.  Tissue distribution of teneligliptin in rats and comparisons with data reported for other dipeptidyl peptidase‐4 inhibitors 
The tissue distribution of teneligliptin, a dipeptidyl peptidase (DPP)‐4 inhibitor, was investigated in rats, and compared with tissue distributions previously reported for other DPP‐4 inhibitors. Following the oral administration of [14C]teneligliptin to Sprague–Dawley rats, it was predominantly distributed to the kidney and liver, followed by the lung, spleen and pituitary gland. The elimination half‐life (t 1/2) of [14C]teneligliptin was 68.3 and 69.0 h in the kidney and liver, respectively; these values were about 10 times greater than the plasma t 1/2. Of note, the elimination of [14C]teneligliptin from tissues with high DPP‐4 activity (kidney, liver and lung) was slower in wild‐type rats than in DPP‐4‐deficient rats, especially in the kidney. By contrast, in the heart and pancreas, which weakly express DPP‐4, no difference was observed in [14C]teneligliptin concentrations between the two animal strains. In the kidney, most radioactivity was attributable to unchanged teneligliptin from 0.5 to 72 h after administration. The marked difference in the distribution of [14C]teneligliptin between the two strains suggests that the high binding affinity of teneligliptin for DPP‐4 is involved in its tissue distribution. The currently marketed DPP‐4 inhibitors are highly distributed to the liver, kidney and lung, but the extent of tissue distribution varies greatly among the drugs. The differences in the tissue distributions of DPP‐4 inhibitors might be related to differences in their pleiotropic effects. © 2016 The Authors Biopharmaceutics & Drug Disposition Published by John Wiley & Sons Ltd.
PMCID: PMC5074247  PMID: 26749565
DPP‐4 inhibitor; tissue distribution; teneligliptin
2.  Challenges and advances in the assessment of the disposition of antibody‐drug conjugates 
Antibody‐drug conjugates (ADCs) are a rapidly growing therapeutic platform for the treatment of cancer. ADCs consist of a cytotoxic small molecule drug linked to an antibody to provide targeted delivery of the cytotoxic agent to the tumor. Understanding the pharmacokinetics (PK) and pharmacodynamics (PD) of ADCs is crucial in their design to optimize dose and regimen, to maximize efficacy and to minimize toxicity in patients. Significant progress has been made in recent years in this area, however, many fundamental questions still remain. This review discusses factors to consider while assessing the disposition of ADCs, and the unique challenges associated with these therapeutics. Current tools that are available and strategies to enable appropriate assessment are also discussed. © 2015 Genentech Inc. Biopharmaceutics & Drug Disposition Published by John Wiley & Sons Ltd.
PMCID: PMC5032988  PMID: 25904406
antibody drug conjugate; pharmacokinetics; preclinical; biotherapeutics; cancer
3.  A Physiologically Based Pharmacokinetic Model to Predict the Pharmacokinetics of Highly Protein-Bound Drugs and Impact of Errors in Plasma Protein Binding 
Predicting the pharmacokinetics of highly protein-bound drugs is difficult. Also, since historical plasma protein binding data was often collected using unbuffered plasma, the resulting inaccurate binding data could contribute to incorrect predictions. This study uses a generic physiologically based pharmacokinetic (PBPK) model to predict human plasma concentration-time profiles for 22 highly protein-bound drugs. Tissue distribution was estimated from in vitro drug lipophilicity data, plasma protein binding, and blood: plasma ratio. Clearance was predicted with a well-stirred liver model. Underestimated hepatic clearance for acidic and neutral compounds was corrected by an empirical scaling factor. Predicted values (pharmacokinetic parameters, plasma concentration-time profile) were compared with observed data to evaluate model accuracy. Of the 22 drugs, less than a 2-fold error was obtained for terminal elimination half-life (t1/2, 100% of drugs), peak plasma concentration (Cmax, 100%), area under the plasma concentration-time curve (AUC0–t, 95.4%), clearance (CLh, 95.4%), mean retention time (MRT, 95.4%), and steady state volume (Vss, 90.9%). The impact of fup errors on CLh and Vss prediction was evaluated. Errors in fup resulted in proportional errors in clearance prediction for low-clearance compounds, and in Vss prediction for high-volume neutral drugs. For high-volume basic drugs, errors in fup did not propagate to errors in Vss prediction. This is due to the cancellation of errors in the calculations for tissue partitioning of basic drugs. Overall, plasma profiles were well simulated with the present PBPK model.
PMCID: PMC4844798  PMID: 26531057
Physiologically based pharmacokinetic (PBPK) modeling; Protein binding; Distribution volume; hepatic metabolism
4.  Population Pharmacokinetics of Etomidate in Neonates and Infants with Congenital Heart Disease 
Etomidate is a rapid-onset, short-acting hypnotic medication administered for induction of anesthesia. It is currently approved by the Food and Drug Administration for use in older children and adults. Pharmacokinetic data to help guide dosing in neonates and infants is lacking.
The aim of this study was to determine the pharmacokinetics of etomidate in neonates and infants with congenital heart disease undergoing cardiac surgery.
Four neonates and sixteen infants, postnatal age 0.3 – 11.7 months, requiring open-heart surgery received 0.3 mg/kg of etomidate administered as a single intravenous dose prior to surgery. Blood sampling for plasma etomidate concentration occurred immediately following etomidate administration until the initiation of cardiopulmonary bypass. A population pharmacokinetic approach using nonlinear mixed–effects modeling was applied to characterize etomidate pharmacokinetics.
The pharmacokinetics of etomidate was described by a two-compartment model with first-order elimination. An allometric weight-based model was applied to scale results to a 70 kg adult. Covariates including age and cardiac physiology were not found to significantly impact etomidate pharmacokinetics. The study population was found to have a central and intercompartmental clearance of 0.624 L/min/70-kg and 0.44 L/min/70-kg, respectively; central and peripheral distribution volume of 9.47 and 22.8 L/70-kg, respectively. Inter-individual variability was between 94–142% for all parameters and residual variability was 29%.
The clearance of etomidate is lower in neonates and infants with congenital heart disease compared to published values for older children without congenital heart disease. In addition, etomidate pharmacokinetics is highly variable in this pediatric cardiac population.
PMCID: PMC4629917  PMID: 25377074
etomidate; pharmacokinetics; infant; newborn; congenital heart defects
5.  Effects of hypertonic buffer composition on lymph node uptake and bioavailability of rituximab, after subcutaneous administration 
Subcutaneous administration of biologics is highly desirable; however, incomplete bioavailability after sc administration remains a major challenge. In this work we investigated the effects of excipient dependent hyper-osmolarity on lymphatic uptake and plasma exposure of rituximab as a model protein. Using Swiss Webster (SW) mice as our animal model, we compared the effects of NaCl, mannitol and, O-Phospho-L-Serine (OPLS) on plasma concentration of rituximab over 5 days after sc administration. We observed an increase in plasma concentrations in animals administered rituximab in hypertonic buffer solutions, as compared to isotonic buffer. Bioavailability, as estimated by our pharmacokinetic model, increased from 29% in isotonic buffer to 54% in hypertonic buffer containing NaCl, to almost complete bioavailability in hypertonic buffers containing high dose OPLS or mannitol. This improvement in plasma exposure is due to improved lymphatic trafficking as evident from the increase in the fraction of dose trafficked through the lymph node in the presence of hypertonic buffers. The fraction of the dose trafficked through the lymphatic, as estimated by the model, increased from 0.05 % in isotonic buffer to 13% in hyper-tonic buffer containing NaCl to about 30% for hypertonic buffers containing high dose OPLS and mannitol. Our data suggests that hypertonic solutions may be a viable option to improve sc bioavailability.
PMCID: PMC4643658  PMID: 25377184
Biologics; O-Phospho-L-Serine (OPLS); mannitol; osmolarity; lymphatic uptake
6.  Mechanistic analysis of solute transport in an in vitro physiological two-phase dissolution apparatus 
In vitro dissolution methodologies that adequately capture the oral bioperformance of solid dosage forms are critical tools needed to aid formulation development. Such methodologies must encompass important physiological parameters and be designed with drug properties in mind. Two-phase dissolution apparatuses, which contain an aqueous phase in which the drug dissolves (representing the dissolution/solubility component) and an organic phase into which the drug partitions (representing the absorption component), have the potential to provide meaningful predictions of in vivo oral bioperformance for some BCS II, and possibly some BCS IV drug products. Before such an apparatus can be evaluated properly, it is important to understand the kinetics of drug substance partitioning from the aqueous to the organic medium. A mass transport analysis was performed of the kinetics of partitioning of drug substance solutions from the aqueous to the organic phase of a two-phase dissolution apparatus. Major assumptions include pseudo-steady-state conditions, a dilute aqueous solution and diffusion-controlled transport. Input parameters can be measured or estimated a priori. This paper presents the theory and derivation of our analysis, compares it with a recent kinetic approach, and demonstrates its effectiveness in predicting in vitro partitioning profiles of three BCS II weak acids in four different in vitro two-phase dissolution apparatuses. Very importantly, the paper discusses how a two-phase apparatus can be scaled to reflect in vivo absorption kinetics and for which drug substances the two-phase dissolution systems may be appropriate tools for measuring oral bioperformance.
PMCID: PMC4503256  PMID: 22847296
dissolution; oral absorption; two-phase; biphasic; physiological
7.  Proposal for defining the relevance of drug accumulation derived from single dose study data for modified release dosage forms 
Recently, the European Medicines Agency (EMA) published the new draft guideline on the pharmacokinetic and clinical evaluation of modified release (MR) formulations. The draft guideline contains the new requirement of performing multiple dose (MD) bioequivalence studies, in the case when the MR formulation is expected to show ‘relevant’ drug accumulation at steady state (SS). This new requirement reveals three fundamental issues, which are discussed in the current work: first, measurement for the extent of drug accumulation (MEDA) predicted from single dose (SD) study data; second, its relationship with the percentage residual area under the plasma concentration–time curve (AUC) outside the dosing interval (τ) after SD administration, %AUC(τ-∞)SD; and third, the rationale for a threshold of %AUC(τ-∞)SD that predicts ‘relevant’ drug accumulation at SS. This work revealed that the accumulation ratio RA,AUC, derived from the ratio of the time-averaged plasma concentrations during τ at SS and after SD administration, respectively, is the ‘preferred’ MEDA for MR formulations. A causal relationship was derived between %AUC(τ-∞)SD and RA,AUC, which is valid for any drug (product) that shows (dose- and time-) linear pharmacokinetics regardless of the shape of the plasma concentration–time curve. Considering AUC thresholds from other guidelines together with the causal relationship between %AUC(τ-∞)SD and RA,AUC indicates that values of %AUC(τ-∞)SD ≤ 20%, resulting in RA,AUC ≤ 1.25, can be considered as leading to non-relevant drug accumulation. Hence, the authors suggest that 20% for %AUC(τ-∞)SD is a reasonable threshold and selection criterion between SD or MD study designs for bioequivalence studies of new MR formulations. © 2014 The Authors Biopharmaceutics & Drug Disposition Published by John Wiley & Sons Ltd.
PMCID: PMC4405076  PMID: 25327367
pharmacokinetics; noncompartmental analysis; drug accumulation; modified release
8.  Nonlinear pharmacokinetics of Factor VIII and its phosphatidylinositol lipidic complex in hemophilia A mice 
Factor VIII (FVIII) is an important cofactor in the blood coagulation cascade and its deficiency or dysfunction causes Hemophilia A (HA), a bleeding disorder. Replacement with recombinant FVIII is limited by a short half-life and the development of inhibitory antibodies. We have developed a phosphatidylinositol (PI) containing lipid nanoparticle that, when associated with FVIII, reduces immunogenicity and prolongs circulation of the therapeutic protein in HA mice. Here, we conducted a multiple dose level pharmacokinetic (PK)study of human free FVIII and its FVIII-PI complex over a clinically relevant range of doses (20, 40, and 200 IU/kg) in HA mice to investigate linearity of the PK and to determine if reduced catabolism of FVIII following association with PI particles, previously only observed in the terminal phase following 400 IU/kg, could be extendable over a range of doses. Our findings suggest that the disposition of FVIII is best characterized by a two-compartment model with saturableMichaelis-Mentenelimination. Spontaneous complexation of FVIII with PI particles significantly increases plasma survival of the proteinat 20 and 40 IU/kg doses. Human simulations at 40 IU/kg project an increase in terminal half-life and time to reach a minimum therapeutic threshold of 0.01 IU/mL of 5.4 h and 40 h respectively compared to free FVIII. Formulation with PI containing lipid particles may represent a viable delivery strategy for improving FVIII therapy.
PMCID: PMC3976741  PMID: 24259187
9.  Pharmacokinetic Interaction between Efavirenz and Dual Protease Inhibitors in Healthy Volunteers 
The combination of efavirenz with HIV-1 protease inhibitors (PI) results in complex interactions secondary to mixed induction and inhibition of oxidative metabolism. ACTG A5043 was a prospective, open-label, controlled, two-period, multiple-dose study with 55 healthy volunteers. The objective of the present study was to evaluate the potential pharmacokinetic interaction between efavirenz and dual PIs. The subjects received a daily dose of 600 mg efavirenz for 10 days with amprenavir 600 mg twice daily added at day 11 and were randomized to receive nelfinavir, indinavir, ritonavir, saquinavir, or no second PI on days 15–21. Intensive pharmacokinetic studies were conducted on day 14 and 21. Efavirenz plasma concentrations were fit to candidate models using weighted non-linear regression. The disposition of efavirenz was described by a linear two-compartment model with first order absorption following a fitted lag time. Apparent clearance (CLt/F), volume of distribution at steady state (Vss/F), inter-compartmental clearance, and the central and peripheral volume of distribution were estimated. The mean CLt/F and Vss/F of efavirenz were 0.126 l/h/kg and 4.412 l/kg, respectively. Both AUC and CLt/F of efavirenz remained unchanged after 7 days of dual PI dosing. The mean Vss/F of efavirenz increased an average of 89% across arms, ranging from 52% (nelfinavir) to 115% (indinavir) relative to efavirenz with amprenavir alone. Increases were also observed in Vp/F after the addition of nelfinavir, indinavir, ritonavir and saquinavir by 85%, 170%, 162% and 111%, respectively. In conclusion, concomitant administration of dual PIs is unlikely to have any clinically significant effect on the pharmacokinetics of CYP2B6 substrates in general or oral efavirenz specifically.
PMCID: PMC4307806  PMID: 18041735
pharmacokinetic modeling; drug interactions; non-nucleoside reverse transcriptase inhibitor; efavirenz; HIV-1 protease inhibitors
10.  Computational Approaches to Analyze and Predict Small Molecule Transport and Distribution at Cellular and Subcellular Levels 
Quantitative structure-activity relationship (QSAR) studies and mechanistic mathematical modeling approaches have been independently employed for analyzing and predicting the transport and distribution of small molecule chemical agents in living organisms. Both of these computational approaches have been useful to interpret experiments measuring the transport properties of small molecule chemical agents, in vitro and in vivo. Nevertheless, mechanistic cell-based pharmacokinetic models have been especially useful to guide the design of experiments probing the molecular pathways underlying small molecule transport phenomena. Unlike QSAR models, mechanistic models can be integrated from microscopic to macroscopic levels, to analyze the spatiotemporal dynamics of small molecule chemical agents from intracellular organelles to whole organs, well beyond the experiments and training data sets upon which the models are based. Based on differential equations, mechanistic models can also be integrated with other differential equations-based systems biology models of biochemical networks or signaling pathways. Although the origin and evolution of mathematical modeling approaches aimed at predicting drug transport and distribution has occurred independently from systems biology, we propose that the incorporation of mechanistic cell-based computational models of drug transport and distribution into a systems biology modeling framework is a logical next-step for the advancement of systems pharmacology research.
PMCID: PMC3947293  PMID: 24218242
Cellular pharmacokinetics; Computational modeling; Drug Transport; Systems pharmacology
11.  Pharmacokinetics of Methylprednisolone after Intravenous and Intramuscular Administration in Rats 
Methylprednisolone (MPL) pharmacokinetics was examined in adrenalectomized (ADX) and normal rats to assess the feasibility of intramuscular (i.m.) dosing for use in pharmacodynamic studies. Several study phases were pursued. Parallel group studies were performed in normal and ADX rats given 50 mg/kg MPL (i.v. or i.m.) and blood samples were collected up to 6 h. Data from studies where normal rats were dosed with 50 mg/kg MPL i.m. and killed over either 6 or 96 h were combined to determine muscle site and plasma MPL concentrations. Lastly, ADX rats were dosed with 50 mg/kg MPL i.m. and killed over 18 h to assess hepatic tyrosine aminotransferase (TAT) dynamics. MPL exhibited bi-exponential kinetics after i.v. dosing with a terminal slope of 2.1 h−1. The i.m. drug was absorbed slowly with two first-order absorption rate constants, 1.26 and 0.219 h−1 indicating flip-flop kinetics with overall 50% bioavailability. The kinetics of MPL at the injection site exhibited slow, dual absorption rates. Although i.m. MPL showed lower bioavailability compared with other corticosteroids in rats, TAT dynamics revealed similar i.m. and i.v. response profiles. The more convenient intramuscular dosing can replace the i.v. route without causing marked differences in pharmacodynamics.
PMCID: PMC4181331  PMID: 17569107
methylprednisolone; corticosteroids; pharmacokinetics; intramuscular injection; tyrosine aminotransferase
12.  Comparison of Dexamethasone Pharmacokinetics in Female Rats after Intravenous and Intramuscular Administration 
This study seeks a route of drug administration that would produce a pharmacokinetic profile for dexamethasone not significantly different from the intravenous route in female rats and would offer reproducible drug input with minimal stress to the animals. The intramuscular (IM) route of drug administration vs intravenous (IV) injection were compared in three female Wistar rats administered 1 mg/kg dexamethasone phosphate. Dexamethasone plasma concentrations were measured by a normal phase HPLC assay for 12 h after drug administration. Dexamethasone exhibited monoexponential behavior after intravenous dosing and was absorbed rapidly after intramuscular dosing (absorption half-life of 14 min) with 86% bioavailability. Dexamethasone had a terminal half-life of 2.3 h after drug administration by either route. The volume of distribution of 0.78 l/kg and the clearance of 0.23 l/h/kg are in good agreement with reported pharmacokinetic parameters in male rats. Intravenous dosing can be replaced by intramuscular dosing without causing any marked difference in dexamethasone pharmacokinetics.
PMCID: PMC4178533  PMID: 15654687
pharmacokinetics; dexamethasone; rats; gender; intramuscular
13.  Changes in clearance, volume and bioavailability of immunosuppressants when given with HAART in HIV-1 infected liver and kidney transplant recipients 
Solid organ transplantation in Human Immunodeficiency Virus 1 (HIV)-infected individuals requiring concomitant use of immunosuppressants (IS) [e.g., cyclosporine (CsA) or tacrolimus (TAC)] and antiretrovirals (ARVs) [e.g., protease inhibitors (PIs) and/or non-nucleoside reverse transcriptase inhibitors (NNRTIs)] is complicated by significant drug interactions. We describe the pharmacokinetics of CsA and TAC in 52 patients on both IS and NNRTIs, PIs, or combined NNRTIs+PIs, in studies conducted at 2 weeks, 3, 6, 12 and 24 months after transplantation. CsA and TAC blood concentrations were measured by LC/MS/MS. This multisubject, varied ARV-IS drug combination, longitudinal observational patient study provided a unique opportunity to examine the effect of different ARV drugs on IS PK by comparing ratios of parameters over time and between PK parameters. Subjects taking concomitant PIs exhibited increases in CsA and TAC exposure (AUC/dose) due to increased apparent oral bioavailability and decreased apparent oral clearance. Those subjects taking CsA and concomitant efavirenz (EFV) showed time dependent increases in exposure due to ~30% increases in apparent oral bioavailability over time as well as decreased apparent oral clearance, while subjects on TAC and EFV showed time-dependent changes in all PK parameters. The increased bioavailability was not observed in patients on CsA and nevirapine (NVP). These differences between IS drugs and the changes in PK parameters are not easily predicted, illustrating the importance of continued therapeutic drug monitoring in these patients on these complex medication regimens.
PMCID: PMC4018225  PMID: 24030928
immunosuppressants; antiretrovirals; pharmacokinetics; drug interactions; HIV
14.  Pharmacokinetics, pharmacodynamics, and toxicities of methotrexate in healthy and collagen-induced arthritic rats 
Biopharmaceutics & drug disposition  2013;34(4):10.1002/bdd.1838.
Methotrexate (MTX) is an anchor drug used to treat rheumatoid arthritis (RA), but responsiveness is variable in effectiveness and toxicity. Methotrexate and its polyglutamate conjugates (MTXPGn) in red blood cells (RBC) have been associated with patient response. In the current study, 13 collagen-induced arthritic (CIA) rats and 12 healthy rats were given subcutaneous doses of either saline or 0.3 or 1.5 mg/kg per 2 days of MTX from day 21 to 43 post-induction. Blood samples were obtained at various times to measure MTX in plasma, and MTX and MTXPGn in RBC. Effects on disease progression were indicated by body weight and paw size. After multiple-doses, RBC MTX reached steady-state (82.4 nM) within 4 days. The MTXPG2 and MTXPG3 in RBC kept increasing until the end of the study attaining 12.5 and 17.7 nM. Significant weight loss was observed after dosing of 1.5 mg/kg/2 days, whereas moderate effectiveness was observed after dosing of 0.3 mg/kg/2 days. A pharmacokinetic/ pharmacodynamic/disease (PK/PD/DIS) model with indirect mechanisms and transduction components incorporating plasma MTX, RBC MTX, and RBC MTXPGn concentrations, and paw size was developed using naïve data pooling and ADAPT 5. The PK/PD in CIA rats dosed at 0.3 mg/kg/2 days were captured well by our proposed model. MTX showed modest (Imaxd = 0.16) but sensitive (IC50d = 0.712 nM) effectiveness on paw edema. The higher dose produced toxicity. The proposed model offers improved understanding of MTX effects on rheumatoid arthritis.
PMCID: PMC3656137  PMID: 23456770
Methotrexate; rheumatoid arthritis; pharmacokinetics; pharmacodynamics; disease progression
15.  Interaction between HIV Protease Inhibitors (PIs) and Hepatic Transporters in Sandwich Cultured Human Hepatocytes: Implication for PI-based DDIs 
Although HIV protease inhibitors (PIs) produce profound metabolic interactions through inactivation/inhibition of CYP3A enzymes, their role as victims of transporter-based drug-drug interactions (DDIs) is less well understood. Therefore, we investigated if the PIs, nelfinavir (NFV), ritonavir (RTV), lopinavir (LPV), or amprenavir (APV) were transported into sandwich-cultured human hepatocytes (SCHH), and whether OATPs contributed to this transport. Our findings showed that except for 3H-APV, no significant decrease in the total hepatocyte accumulation of the 3H-PIs was detected in the presence of the corresponding unlabeled PI, indicating that the uptake of the other PIs was not mediated. Further, hepatocyte biliary efflux studies using 3H-APV and unlabeled APV confirmed this decrease to be due to inhibition of sinusoidal influx transporter(s) and not the canalicular efflux transporters. Moreover, this sinusoidal transport of APV was not OATP-mediated. Our results indicate the hepatic uptake of NFV, RTV, or LPV was primarily mediated by passive diffusion. APV’s hepatic uptake was mediated by an unidentified sinusoidal transporter(s). Therefore, NFV, RTV or LPV will not be victims of DDIs involving inhibition of hepatic influx transporters; however, the disposition of APV may be affected if its sinusoidal transport is inhibited.
PMCID: PMC3625464  PMID: 23280499
16.  In Silico Prediction of Drug Dissolution and Absorption with variation in Intestinal pH for BCS Class II Weak Acid Drugs: Ibuprofen and Ketoprofen§ 
The FDA Biopharmaceutical Classification System guidance allows waivers for in vivo bioavailability and bioequivalence studies for immediate-release solid oral dosage forms only for BCS class I. Extensions of the in vivo biowaiver for a number of drugs in BCS Class III and BCS class II have been proposed, particularly, BCS class II weak acids. However, a discrepancy between the in vivo- BE results and in vitro- dissolution results for a BCS class II acids was recently observed. The objectives of this study were to determine the oral absorption of BCS class II weak acids via simulation software and to determine if the in vitro dissolution test with various dissolution media could be sufficient for in vitro bioequivalence studies of ibuprofen and ketoprofen as models of carboxylic acid drugs.
The oral absorption of these BCS class II acids from the gastrointestinal tract was predicted by GastroPlus™. Ibuprofen did not satisfy the bioequivalence criteria at lower settings of intestinal pH=6.0. Further the experimental dissolution of ibuprofen tablets in the low concentration phosphate buffer at pH 6.0 (the average buffer capacity 2.2 mmol L-1/pH) was dramatically reduced compared to the dissolution in SIF (the average buffer capacity 12.6 mmol L -1/pH). Thus these predictions for oral absorption of BCS class II acids indicate that the absorption patterns largely depend on the intestinal pH and buffer strength and must be carefully considered for a bioequivalence test. Simulation software may be very useful tool to aid the selection of dissolution media that may be useful in setting an in vitro bioequivalence dissolution standard.
PMCID: PMC3466597  PMID: 22815122
weak acid; ibuprofen; ketoprofen; pH; simulation; GastroPlus; in vitro dissolution; dissolution media
17.  Pharmacokinetics of salsalate and salicylic acid in normal and diabetic rats 
The pharmacokinetics (PK) of salsalate (SS) and salicylic acid (SA) was assessed in normal Wistar and diabetic Goto-Kakizaki rats. Three PK studies were conducted: 1) PK of SA in normal rats after intravenous dosing of SA at 20, 40, 80 mg/kg. 2) PK of SS and SA in normal rats after oral dosing of SS at 28, 56, 112 mg/kg. 3) PK during 4 months feeding of SS-containing diet in both normal and diabetic rats. The disposition of SS and SA were simultaneously evaluated using a pharmacokinetic model comprised of several transit absorption steps and linear and nonlinear dual elimination pathways for SA. The results indicated that the nonlinear elimination pathway of SA only accounted for a small fraction of the total clearance (< 12%) at therapeutic concentrations. A flat profile of SA was observed after oral dosing SS, particularly at a high dose. The possible reasons for this flat profile were posed. During the SS-diet feeding, diabetic rats achieved lower blood concentrations of SA than normal rats with a higher apparent clearance (CL/F) possibly due to incomplete (47%) bioavailability. Such CL/F decreased with age in both diabetic and normal rats. The effect of diabetes on SA pharmacokinetics may necessitate increased dosing in future usage of SS in diabetes.
PMCID: PMC3440557  PMID: 22782506
salsalate; salicylic acid; pharmacokinetics; diabetes
18.  Pharmacokinetics of Dexamethasone in a Rat Model of Rheumatoid Arthritis 
Dexamethasone (DEX) is often given for the treatment of rheumatoid arthritis and clinical dosing regimens of DEX have often been based empirically. This study tests whether the inflammation processes in a rat model of rheumatoid arthritis alters the clearance and volume of distribution of DEX when compared with healthy controls. Groups of healthy and arthritic male Lewis rats received either a low (0.225 mg/kg) or high (2.25 mg/kg) intramuscular dose of DEX. Arthritis was induced by intradermal injection of type II porcine collagen in incomplete Freund's adjuvant emulsion at the base of the tail. DEX was dosed in the arthritic animals 22 days post arthritis induction. Plasma DEX concentrations were determined by HPLC. Plasma concentration versus time data were analysed by non-compartmental analysis and pharmacokinetic model fitting using the population pharmacokinetic software NONMEM V. A linear bi-exponential pharmacokinetic model with extravascular input described the data for both healthy and arthritic animals. Clearance was the only parameter determined statistically different between both groups (healthy=1.05 l/h/kg, arthritic=1.19 l/h/kg). The steady-state volume of distribution for both groups was 4.85 l/kg. The slight difference in clearance was visibly undetectable and unlikely to produce meaningful changes in DEX disposition in arthritic rats.
PMCID: PMC3712282  PMID: 18613033
dexamethasone; pharmacokinetics; arthritis; collagen
19.  Pharmacodynamics of Glucose Regulation by Methylprednisolone. I. Adrenalectomized Rats 
Mechanisms related to the adverse effects of corticosteroids on glucose homeostasis were studied. Five groups of adrenalectomized (ADX) rats were given methylprednisolone (MPL) intravenously at 10 and 50 mg/kg, or a continuous 7 day infusion at rates of 0, 0.1, 0.3 mg/kg/h via subcutaneously implanted Alzet mini-pumps. Plasma concentrations of MPL, glucose and insulin were determined at various time points up to 72 h after injection or 336 h after infusion. The pharmacokinetics of MPL was captured with a two-compartment model. The Adapt II software was used in modeling. Injection of MPL caused a temporary glucose increase over 6 h by stimulating gluconeogenesis. The glucose changes stimulated pancreatic β-cell secretion yielding a later insulin peak at around 10 h. In turn, insulin can stimulate glucose disposition. However, long-term MPL treatment caused continuous hyperglycemia during and after infusion. Insulin was increased during infusion, and immediately returned to baseline after the infusion was terminated, despite the almost doubled glucose concentration. A disease progression model incorporating the reduced endogenous glucose disposition was included to capture glucose homeostasis under different treatments. The results exemplify the importance of the steroid dosing regimen in mediating pharmacological and adverse metabolic effects. This mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model quantitatively describes the induction of hyperglycemia and provides additional insights into metabolic disorders such as diabetes.
PMCID: PMC3712292  PMID: 19156931
corticosteroids; methylprednisolone; pharmacodynamics; pharmacokinetics; glucose; insulin
20.  Pharmacodynamics of Glucose Regulation by Methylprednisolone. II. Normal Rats 
A physiologic pharmacodynamic model was developed to jointly describe the effects of methylprednisolone (MPL) on adrenal suppression and glycemic control in normal rats. Six groups of animals were given MPL intravenously at 0, 10 and 50 mg/kg, or by subcutaneous 7 day infusion at rates of 0, 0.1 and 0.3 mg/kg/h. Plasma concentrations of MPL, corticosterone (CST), glucose and insulin were determined at various times up to 72 h after injection and 336 h after infusion. The pharmacokinetics of MPL was described by a two-compartment model. A circadian rhythm for CST was found in untreated rats with a stress-altered baseline caused by handling, which was captured by a circadian harmonic secretion rate with an increasing mesor. All drug treatments caused CST suppression. Injection of MPL caused temporary increases in glucose over 4 h. Insulin secretion was thereby stimulated yielding a later peak around 6 h. In turn, insulin can normalize glucose. However, long-term dosing caused continuous hyperglycemia during and after infusion. Hyperinsulinemia was achieved during infusion, but diminished immediately after dosing despite the high glucose concentration. The effects of CST and MPL on glucose production were described with a competitive stimulation function. A disease progression model incorporating reduced endogenous glucose uptake/utilization was used to describe glucose metabolism under different treatments. The results exemplify the roles of endogenous and exogenous hormones in mediating glucose dynamics. The pharmacokinetic/pharmacodynamic model is valuable for quantitating diabetogenic effects of corticosteroid treatments and provides mechanistic insights into the hormonal control of the metabolic system.
PMCID: PMC3712293  PMID: 19156669
corticosterone; methylprednisolone; pharmacodynamics; pharmacokinetics; glucose; insulin
21.  Chemopreventive and anti-angiogenic effects of dietary phenethyl isothiocyanate in an N-methyl nitrosourea-induced breast cancer animal model 
The effect of phenethyl isothiocyanate (PEITC), a component of cruciferous vegetables, on the initiation and progression of cancer was investigated in a chemically induced estrogen-dependent breast cancer model. Breast cancer was induced in female Sprague Dawley rats (8 weeks old) by the administration of N-methyl nitrosourea (NMU). Animals were administered 50 or 150 µmol/kg oral PEITC and monitored for tumor appearance for 18 weeks. The PEITC treatment prolonged the tumor-free survival time and decreased the tumor incidence and multiplicity. The time to the first palpable tumor was prolonged from 69 days in the control, to 84 and 88 days in the 50 and 150 µmol/kg PEITC-treated groups. The tumor incidence in the control, 50 µmol/kg, and 150 µmol/kg PEITC-treated groups was 56.6%, 25.0% and 17.2%, while the tumor multiplicity was 1.03, 0.25 and 0.21, respectively. Differences were statistically significant (p < 0.05) from the control, but there were no significant differences between the two dose levels. The intratumoral capillary density decreased from 4.21 ± 0.30 vessels per field in the controls to 2.46 ± 0.25 in the 50 µmol/kg and 2.36 ± 0.23 in the 150 µmol/kg PEITC-treated animals. These studies indicate that supplementation with PEITC prolongs the tumor-free survival, reduces tumor incidence and burden, and is chemoprotective in NMU-induced estrogen-dependent breast cancer in rats. For the first time, it is reported that PEITC has anti-angiogenic effects in a chemically induced breast cancer animal model, representing a potentially significant mechanism contributing to its chemopreventive activity.
PMCID: PMC3705647  PMID: 23138465
phenethyl isothiocyanate; estrogen-dependent breast cancer model; anti-angiogenic effects; N-methyl nitrosourea; PEITC; NMU
22.  ABC Transporters and Isothiocyanates: Potential for Pharmacokinetic Diet–Drug Interactions 
Isothiocyanates, a class of anti-cancer agents, are derived from cruciferous vegetables such as broccoli, cabbage and watercress, and have demonstrated chemopreventive activity in a number of cancer models and epidemiologic studies. Due to public interest in cancer prevention and alternative therapies in cancer, the consumption of herbal supplements and vegetables containing these compounds is widespread and increasing. Isothiocyanates interact with ATP-binding cassette (ABC) efflux transporters such as P-glycoprotein, MRP1, MRP2 and BCRP, and may influence the pharmacokinetics of substrates of these transporters. This review discusses the pharmacokinetic properties of isothiocyanates, their interactions with ABC transporters, and presents some data describing the potential for isothiocyanate-mediated diet–drug interactions.
PMCID: PMC3694332  PMID: 19623673
isothiocyanates; ABC transporters; pharmacokinetics; diet-drug interactions
23.  Pharmacodynamic analysis of stress erythropoiesis: change in erythropoietin receptor pool size following double phlebotomies in sheep 
Biopharmaceutics & drug disposition  2011;32(3):10.1002/bdd.743.
A feedback receptor regulation model was incorporated into a pharmacodynamic model to describe the stimulation of hemoglobin (Hb) production by endogenous erythropoietin (EPO). The model considers the dynamic changes that take place in the EPO receptor (EPOR) pool under phlebotomy-induced anemia. Using a 125I-rhEPO tracer the EPO clearance changes are evaluated longitudinally prior to and following phlebotomy-induced anemia to indirectly evaluate changes in the EPOR pool size, which has been shown to be linearly related to the clearance. The proposed model simultaneously captures the general behavior of temporal changes in Hb relative to EPO plasma clearance in five lambs (r=0.95), while accounting for the confounding variables of phlebotomy and changes in the blood volume in the growing animals. The results indicate that under anemia the EPOR pool size is up-regulated by a factor of nearly two over baseline and that the lowest and highest EPOR pool sizes differ by a factor of approximately four. The kinetic model developed and the data-driven mechanism proposed serves as a starting point for developing an optimal EPO dosing algorithm for the treatment of neonatal anemia.
PMCID: PMC3657587  PMID: 21456051
Erythropoietin receptor; Dosing optimization; Pharmacodynamics; Pharmacokinetics; sheep
24.  Differential pharmacokinetic analysis of in vivo erythropoietin receptor interaction with erythropoietin and continuous erythropoietin receptor activator in sheep 
The two erythropoiesis stimulating agents (ESAs), short acting recombinant human erythropoietin (EPO) and long acting continuous erythropoietin receptor activator (CERA), have been hypothesized to share an in vivo elimination pathway that involves binding to erythropoietin receptor (EPOR) and subsequent internalization. A physiologically based recirculation model and a pharmacokinetic tracer interaction methodology (TIM) were used to compare the in vivo interaction kinetics with EPOR between the two ESAs in adult sheep. Animals treated with EPO experienced a greater EPOR up-regulation than those treated with CERA, as evidenced by an eightfold-higher initial EPOR normalized production rate constant, ksyn/R0, versus a twofold-larger EPOR degradation rate constant, kdeg. In agreement with in vitro studies, EPO had a lower in vivo equilibrium dissociation constant from EPOR than CERA (KD = 6 versus 88.4 pmol/l, respectively, p < 0.01). The internalization and/or degradation of the EPO–EPOR complex was faster than that of the CERA–EPOR complex (kint = 24 versus 2.41 h−1, respectively, p < 0.01). The adopted model enables a mechanism-based explanation for CERA’s slower elimination and greater erythropoietic activity in vivo. As predicted by the model, the slower elimination of CERA is due to: (1) less EPOR up-regulation induced by CERA administration; (2) slower binding of CERA to EPOR; and (3) reduced internalization and/or degradation rate of surface-bound CERA. Slower CERA/EPOR complex elimination explains the greater in vivo erythropoiesis reported for CERA, despite its lower affinity to EPOR. A sensitivity analysis showed that the model parameters were reliably estimated using the TIM methodology.
PMCID: PMC3616385  PMID: 21678432
erythropoietin; erythropoiesis stimulating agent (ESA); CERA; pharmacokinetics; receptor; physiological model; receptor binding; recirculation model
25.  Metabolism, oral bioavailability and pharmacokinetics of chemopreventive kaempferol in rats 
The purpose of this study was to compare the hepatic and small intestinal metabolism, and examine bioavailability and gastro-intestinal first-pass effects of Kaempferol in the rats. Liver and small intestinal microsomes fortified with either NADPH or UDPGA were incubated with varying concentrations of Kaempferol for upto 120 minutes. Based on the values of the kinetic constants (Km and Vmax), the propensity for UDPGA-dependent conjugation as compared to NADPH-dependent oxidative metabolism was higher for both hepatic and small intestinal microsomes. Male Sprague-Dawley rats were administered Kaempferol intravenously (IV) (10, 25 mg/kg) or orally (100, 250 mg/kg). Gastro-intestinal first pass effects were observed by collecting portal blood after oral administration of 100 mg/kg Kaempferol. Pharmacokinetic parameters were obtained by Noncompartmental analysis using WinNonlin. After IV administration, the plasma concentration-time profiles for 10 and 25 mg/kg were consistent with high clearance (~ 3 L/hr/kg) and large volumes of distribution (8-12 L/kg). The disposition was characterized by a terminal half-life value of 3-4 hours. After oral administration the plasma concentration-time profiles demonstrated fairly rapid absorption (tmax ~ 1-2 hours). The area under the curve (AUC) values after IV and oral doses increased proportional to the dose. The bioavailability (F) was poor at ~ 2%. Analysis of portal plasma after oral administration revealed low to moderate absorption. Taken together, the low F of Kaempferol is attributed in part to extensive first-pass metabolism by glucuronidation and other metabolic pathways in the gut and in the liver.
PMCID: PMC3580176  PMID: 19722166
Pharmacokinetics; Kaempferol; metabolism; flavonoids; liver; small intestine

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