Interspecies Brain PBPK Modeling Platform to Predict Passive Transport through the Blood-Brain Barrier and Assess Target Site Disposition.

The high failure rate of central nervous system (CNS) drugs is partly associated with an insufficient understanding of target site exposure. Blood-brain barrier (BBB) permeability evaluation tools are needed to explore drugs' ability to access the CNS. An outstanding aspect of physiologically based pharmacokinetic (PBPK) models is the integration of knowledge on drug-specific and system-specific characteristics, allowing the identification of the relevant factors involved in target site distribution. We aimed to qualify a PBPK platform model to be used as a tool to predict CNS concentrations when significant transporter activity is absent and human data are sparse or unavailable. Data from the literature on the plasma and CNS of rats and humans regarding acetaminophen, oxycodone, lacosamide, ibuprofen, and levetiracetam were collected. Human BBB permeability values were extrapolated from rats using inter-species differences in BBB surface area. The percentage of predicted AUC and Cmax within the 1.25-fold criterion was 85% and 100% for rats and humans, respectively, with an overall GMFE of <1.25 in all cases. This work demonstrated the successful application of the PBPK platform for predicting human CNS concentrations of drugs passively crossing the BBB. Future applications include the selection of promising CNS drug candidates and the evaluation of new posologies for existing drugs.

New insights into the role of VKORC1 polymorphisms for optimal warfarin dose selection in Caribbean Hispanic patients through an external validation of a population PK/PD model.

Warfarin, an oral anticoagulant, has been used for decades to prevent thromboembolic events. The complex interplay between CYP2C9 and VKORC1 genotypes on warfarin PK and PD properties is not fully understood in special sub-groups of patients. This study aimed to externally validate a population pharmacokinetic/pharmacodynamic (PK/PD) model for the effect of warfarin on international normalized ratio (INR) and to evaluate optimal dosing strategies based on the selected covariates in Caribbean Hispanic patients. INR, and CYP2C9 and VKORC1 genotypes from 138 patients were used to develop a population PK/PD model in NONMEM. The structural definition of a previously published PD model for INR was implemented. A numerical evaluation of the parameter-covariate relationship was performed. Simulations were conducted to determine optimal dosing strategies for each genotype combinations, focusing on achieving therapeutic INR levels. Findings revealed elevated IC50 for G/G, G/A, and A/A VKORC1 haplotypes (11.76, 10.49, and 9.22 mg/L, respectively), in this population compared to previous reports. The model-guided dosing analysis recommended daily warfarin doses of 3-5 mg for most genotypes to maintain desired INR levels, although subjects with combination of CYP2C9 and VKORC1 genotypes * 2/* 2-, * 2/* 3- and * 2/* 5-A/A would require only 1 mg daily. This research underscores the potential of population PK/PD modeling to inform personalized warfarin dosing in populations typically underrepresented in clinical studies, potentially leading to improved treatment outcomes and patient safety. By integrating genetic factors and clinical data, this approach could pave the way for more effective and tailored anticoagulation therapy in diverse patient groups.

Comprehensive Physiologically Based Pharmacokinetic Model to Assess Drug-Drug Interactions of Phenytoin.

Regulatory agencies worldwide expect that clinical pharmacokinetic drug-drug interactions (DDIs) between an investigational new drug and other drugs should be conducted during drug development as part of an adequate assessment of the drug's safety and efficacy. However, it is neither time nor cost efficient to test all possible DDI scenarios clinically. Phenytoin is classified by the Food and Drug Administration as a strong clinical index inducer of CYP3A4, and a moderate sensitive substrate of CYP2C9. A physiologically based pharmacokinetic (PBPK) platform model was developed using GastroPlus® to assess DDIs with phenytoin acting as the victim (CYP2C9, CYP2C19) or perpetrator (CYP3A4). Pharmacokinetic data were obtained from 15 different studies in healthy subjects. The PBPK model of phenytoin explains the contribution of CYP2C9 and CYP2C19 to the formation of 5-(4'-hydroxyphenyl)-5-phenylhydantoin. Furthermore, it accurately recapitulated phenytoin exposure after single and multiple intravenous and oral doses/formulations ranging from 248 to 900 mg, the dose-dependent nonlinearity and the magnitude of the effect of food on phenytoin pharmacokinetics. Once developed and verified, the model was used to characterize and predict phenytoin DDIs with fluconazole, omeprazole and itraconazole, i.e., simulated/observed DDI AUC ratio ranging from 0.89 to 1.25. This study supports the utility of the PBPK approach in informing drug development.

Leveraging Physiologically Based Modelling to Provide Insights on the Absorption of Paliperidone Extended-Release Formulation under Fed and Fasting Conditions.

Paliperidone was approved by the US FDA in 2006 as an extended-release (ER) tablet (Invega®) for the once-daily treatment of schizophrenia. This osmotic-controlled release oral delivery system (OROS) offers advantages, such as the prevention of plasma concentration fluctuation and reduced dosing frequency. The administration of the ER after a high-fat/high-calorie meal leads to increased maximum plasma concentration and area under the curve values by 60% and 54%, respectively. Food has various effects on gastrointestinal (GI) physiology, including changed transit times, changed volumes, altered pH in different GI compartments, secretion of bile salts, and increased hepatic blood flow. This may affect solubility, the dissolution rate, absorption, and the pharmacokinetics. The aim of this study was to apply physiologically based absorption modeling (PBAM) to provide insights on paliperidone ER absorption under fed and fasting conditions. The PBAM adequately predicted absorption from the OROS formulation under both conditions. Absorption primarily occurs in the ascending colon and caecum. After a high-fat/high-calorie meal, absorption is increased through the jejunum, ileum, and colon due to either increased solubilization or the better efficiency of the OROS technology. PBAM-guided approaches can improve the understanding of branded drugs and thereby aid in guiding the development of generic formulations or formulation alternatives.

Semi-Mechanistic Pharmacokinetic Model to Guide the Dose Selection of Nimotuzumab in Patients with Autosomal Dominant Polycystic Kidney Disease.

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease characterized by an overexpression of epidermal growth factor receptor (EGFR). Nimotuzumab is a recombinant humanized monoclonal antibody against human EGFR. The aim of this study was to develop a population pharmacokinetic model for nimotuzumab and to identify demographic and clinical predictive factors of the pharmacokinetic variability. The population pharmacokinetics (PopPK) of nimotuzumab was characterized using a nonlinear mixed-effect modeling approach with NONMEM®. A total of 422 log-transformed concentration-versus-time datapoints from 20 patients enrolled in a single-center phase I clinical trial were used. Quasi steady state approximation of the full TMDD (target-mediated drug disposition) model with constant target concentration best described the concentration-time profiles. A turnover mediator was included which stimulates the non-specific clearance of mAb in the central compartment in order to explain the reduced levels at higher doses. Covariates had no influence on the PK (pharmacokinetics) parameters. The model was able to detect that the maximum effective dose in ADPKD subjects is 100 mg. The developed PopPK model may be used to guide the dose selection for nimotuzumab during routine clinical practice in patients with polycystic kidney disease. The model will further support the ongoing investigations of the PK/PD relationships of nimotuzumab to improve its therapeutic use in other disease areas.

Assessment of the clinical utility of pharmacogenetic guidance in a comprehensive medication management service.

INTRODUCTION: Pharmacists are poised to be the health care professionals best suited to provide medication-related consults and services based on a patient's genetics. Despite its potential benefits, the implementation of pharmacogenetic (PGx) testing into primary clinical settings has been slow among medically underserved populations. To our knowledge, this is the first time that PGx-driven recommendations have been incorporated into a Comprehensive Medication Management (CMM) service in a Hispanic population. OBJECTIVES: The aim of this study is to evaluate the clinical utility of adding PGx guidance into pharmacist-driven CMM. METHODS: This is a pre- and post-interventional design study. Patients were recruited from a psychologist's clinic. A total of 24 patients had a face-to-face interview with a pharmacist to complete a CMM, Personal Medication Record, and Medication-Related Action Plan (MAP) blind to PGx findings. Collected buccal DNA samples were genotyped using drug-metabolizing enzymes and transporters (DMET) Plus Array. RESULTS: The pharmacist generated new MAPs for each patient based on PGx results. Genetic variants that could potentially affect the safety and effectiveness of at least one drug in the pharmacotherapy were identified in 96% of patients, for whom the pharmacist changed the initial recommendations. Polymorphisms in genes encoding for isoenzymes CYP2D6, CYP2C19, and CYP2C9 were identified in 83%, 52%, and 41% of patients, respectively. Pharmacists performing CMM identified 22 additional medication problems after PGx determinations. Moreover, they agreed with the clinical utility of PGx in the studied sample based on perceived value of adding PGx to traditional CMM and its utility in the decision-making process of pharmacists. CONCLUSIONS: The study confirmed the critical role to be played by pharmacists in facilitating the clinical usage of relevant genetic information to optimize drug therapy decisions as well as their involvement on many levels of these multidisciplinary implementation efforts, including championing and leading PGx-guided CMM services.

Genotype-driven pharmacokinetic simulations of warfarin levels in Puerto Ricans.

Objectives The inter-individual variability of warfarin dosing has been linked to genetic polymorphisms. This study was aimed at performing genotype-driven pharmacokinetic (PK) simulations to predict warfarin levels in Puerto Ricans. Methods Analysis of each individual dataset was performed by one-compartmental modeling using WinNonlin®v6.4. The k e of warfarin given a cytochrome P450 2C9 (CYP2C9) genotype ranged from 0.0189 to 0.0075 h-1. K a and V d parameters were taken from literature. Data from 128 subjects were divided into two groups (i.e., wild-types and carriers) and statistical analyses of PK parameters were performed by unpaired t-tests. Results In the carrier group (n=64), 53 subjects were single-carriers and 11 double-carriers (i.e., *2/*2, *2/*3, *2/*5, *3/*5, and *3/*8). The mean peak concentration (Cmax) was higher for wild-type (0.36±0.12 vs. 0.32±0.14 mg/L). Likewise, the average clearance (CL) parameter was faster among non-carriers (0.22±0.03 vs. 0.17±0.05 L/h; p=0.0001), with also lower area under the curve (AUC) when compared to carriers (20.43±6.97 vs. 24.78±11.26 h mg/L; p=0.025). Statistical analysis revealed a significant difference between groups with regard to AUC and CL, but not for Cmax. This can be explained by the variation of k e across different genotypes. Conclusions The results provided useful information for warfarin dosing predictions that take into consideration important individual PK and genotyping data.

Genotype-driven pharmacokinetic simulations of warfarin levels in Puerto Ricans.

OBJECTIVES: The inter-individual variability of warfarin dosing has been linked to genetic polymorphisms. This study was aimed at performing genotype-driven pharmacokinetic (PK) simulations to predict warfarin levels in Puerto Ricans. METHODS: Analysis of each individual dataset was performed by one-compartmental modeling using WinNonlin®v6.4. The ke of warfarin given a cytochrome P450 2C9 (CYP2C9) genotype ranged from 0.0189 to 0.0075 h-1. Ka and Vd parameters were taken from literature. Data from 128 subjects were divided into two groups (i.e., wild-types and carriers) and statistical analyses of PK parameters were performed by unpaired t-tests. RESULTS: In the carrier group (n=64), 53 subjects were single-carriers and 11 double-carriers (i.e., *2/*2, *2/*3, *2/*5, *3/*5, and *3/*8). The mean peak concentration (Cmax) was higher for wild-type (0.36±0.12 vs. 0.32±0.14 mg/L). Likewise, the average clearance (CL) parameter was faster among non-carriers (0.22±0.03 vs. 0.17±0.05 L/h; p=0.0001), with also lower area under the curve (AUC) when compared to carriers (20.43±6.97 vs. 24.78±11.26 h mg/L; p=0.025). Statistical analysis revealed a significant difference between groups with regard to AUC and CL, but not for Cmax. This can be explained by the variation of ke across different genotypes. CONCLUSIONS: The results provided useful information for warfarin dosing predictions that take into consideration important individual PK and genotyping data.

Pharmacokinetic Evaluation of Nimotuzumab in Patients With Autosomal Dominant Polycystic Kidney Disease.

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease characterized by an overexpression and mislocalization of epidermal growth factor receptor (EGFR) to the apical membranes of cystic epithelial cells. Nimotuzumab is a humanized antibody that recognizes an extracellular domain III of human EGFR. The aim of this study was to assess the pharmacokinetic behavior of nimotuzumab in patients with ADPKD given as a single dose. A phase I, single-center, and noncontrolled open clinical study was conducted. Five patients were enrolled at each of the following fixed-dose levels: 50, 100, 200, and 400 mg. Intravenous continuous infusions of nimotuzumab were administered every 14 days during a year, except the first administration, when blood samples were drawn during 28 days for pharmacokinetic assessments. Subjects were closely monitored during the trial and at completion of the administration of nimotuzumab, including the anti-idiotypic response. For the first time, nimotuzumab was used for treating a nononcological disease. The administration of nimotuzumab showed dose-dependent kinetics. Nimotuzumab does not develop anti-idiotypic response against the murine portion present in the hypervariable region of the antibody present in the serum of the patients treated. No significant differences were found in the systemic clearance between the 100- and 400-mg dose, which indicates that the optimal biological dose is in this range of dose.

Semimechanistic model to characterize nonlinear pharmacokinetics of nimotuzumab in patients with advanced breast cancer.

This study aimed (1) to develop a semimechanistic pharmacokinetic (PK) model for nimotuzumab in patients with advanced breast cancer and (2) to identify demographic, biochemical, and clinical predictive factors of the PK variability. Data from a phase 1 study were analyzed using the nonlinear mixed-effects approach (NONMEM). A target-mediated disposition model that included 2 open PK compartments, the monoclonal antibody (mAb)-target binding, and target and mAb-target complex turnovers best described the linear and nonlinear PK. Covariates had no influence on the PK parameters. The final parameter estimates were 19.93 L (steady-state volume), 0.0045-0.0172 L/h (range of total clearance values), 6.96 µg/mL (steady-state binding constant), 5.50 h(-1) (target degradation rate constant), 1.43 (µg/mL) · h(-1) (complex formation rate), and 0.148 h(-1) (complex internalization rate constant). The model described the effect of the mAb-target binding, and target and mAb-target complex turnovers on nimotuzumab PK. Simulations showed that doses above 200 mg maintained the 50% target occupancy during all of the treatment. This model can be very useful for knowing the dosing schedules required for efficacy and supports further investigation of the pharmacokinetic/pharmacodynamic relationships of nimotuzumab to improve its therapeutic use.

Pharmacokinetics and Biodistribution Study of 7A7 Anti-Mouse Epidermal Growth Factor Receptor Monoclonal Antibody and Its F(ab')(2) Fragment in an Immunocompetent Mouse Model.

Immunocompetent mice, Fc receptor γ-chain deficient mice (Fcer1g(-/-)), and molecular tools as F(ab')(2) bivalent fragments appear as the most suitable biological models to study the mechanisms of the action of anti-epidermal growth factor receptor (EGFR) monoclonal antibodies (mAbs). In vivo experiments contrasting antitumor effects of whole Abs and their bivalent fragments commonly involve a previous comparative pharmacokinetics study. In this paper, pharmacokinetics and biodistribution of an anti-mouse EGFR Ab were assessed using immunocompetent mice. (125)I-labeled 7A7 mAb holds an elimination half-life (t(1/2)ß) of 23.1 h in C57BL/6 mice. Accumulation of mAb was found in liver, spleen, kidneys, and mostly in lungs. We used an ELISA method to determine the t(1/2)ß of a 7A7 mAb using the same experimental setting. Results from this new analysis revealed a t(1/2)ß of 23.9 h, supporting this method as a safer and easier system to evaluate pharmacokinetics parameters of mAbs targeting mouse EGFR. Using this system we also studied pharmacokinetics of 7A7 F(ab')(2) fragment. A tenfold difference between the mAb and fragment t(1/2)ß was found. These data support the use of the 7A7 F(ab')(2) fragment in in vivo studies to explore the contribution of the EGFR signaling blockade and the Fc region to the antitumor effect of 7A7 mAb in this autologous scenario.

Pharmacokinetic comparison of two recombinant human granulocyte colony-stimulating factor after subcutaneous administration in rabbits.

A pharmacokinetic comparison between two formulations (LeukoCIM, CIMAB SA versus Neupogen, Hoffman-La Roche, licensed by Amgen) of recombinant human granulocyte colony-stimulating factor (rhG-CSF) using non-compartmental analysis was performed in male F1 rabbits after a single subcutaneous 11.5 microg/kg dose to help decide whether to conduct further comparability tests. Unlike the absorption phase, a statistical difference was not detected between Neupogen and LeukoCIM for clearance (18.69+/-11.83 versus 28.42+/-12.11 mL/h/kg, P=0.22). In addition, using a multivariate statistical analysis by independent samples test, a significant difference was not found between the two formulations (P=0.88). Finally, the results obtained in this study confirmed the pharmacokinetic comparability between both formulations, supporting the claim for further assessments following the current protocol on biogeneric equivalence.