La greffe de cellules souches hématopoïétiques est parfois le seul traitement curatif dans certaines pathologies pédiatriques telles que les leucémies, les sarcomes, les dédicits immunitaires ou les thalassémies. Le busulfan, un alkylant myéloablatif, fait partie de nombreux protocoles de conditionnement de greffe. C'est un médicament à marge thérapeutique étroite doté d'une forte variabilité pharmacocinétique, qui fait souvent l'objet d'un suivi thérapeutique pharmacologique afin d'optimiser la prise de greffe et d'éviter les risques de maladie veino-occlusive, principale toxicité du busulfan et responsable d'une morbidité et d'une mortalité importante. L'aire sous la courbe, dont il existe un intervalle cible recommandé, est aujourd'hui le paramètre pharmacocinétique utlisé pour effectuer le suivi thérapeutique du busulfan et l'adaptation posologique pendant le conditionnement.L'objectif de notre travail est d'étudier les relations entre la pharmacocinétique du busulfan et ses effets thérapeutiques et toxiques, en particulier la maladie veino-occlusive, et de développer des méthodes d'adaptation posologique pour optimiser l'usage de ce médicament chez l'enfant. Nos travaux ont conduit à plusieurs innovations méthodologiques, avec le développement et la validation d'un modèle pharmacocinétique de population non-paramétrique pour l'adaptation Bayésienne des posologies de busulfan en pédiatrie, et le développement d'une nouvelle méthode de détermination de la dose initiale maximisant la probabilité d'atteindre un intervalle cible d'exposition. Sur le plan clinique, nous avons pu mettre en évidence l'absence de bénéfice clinique de l'utilisation d'un intervalle cible d'exposition plus restreint que celui recommandé. Par ailleurs, nous avons identifié que la survenue de la MVO était liée à la concentration maximale de busulfan, et non à l'aire sous la courbe des concentrations en fonction du temps.L'ensemble de ces résultats est une contribution à l'amélioration de l'utilisation et du suivi thérapeutique pharmacologique du busulfan en onco-hématologie pédiatrique / Hematopoietic stem cell transplantation remains the only curative treatment in many pediatric diseases as leukemia, sarcoma, immunodeficiencies or thalassemia. Busulfan, a myeloablative alkylant, is the cornerstone of pre-transplant conditioning. It has a narrow therapeutic index and a large pharmacokinetic variability. For these reasons, therapeutic drug monitoring is required in order to optimize engraftment and avoid veno-occlusive disease, the main toxicity of busulfan which is responsible of significant morbidity and mortality. Today, the area under the curve, of which there is a target range recommended, is the pharmacokinetic parameter used to carry out therapeutic drug monitoring and dose adjustment during conditioning. Our objective is to investigate relationships between busulfan PK and clinical outcomes, especially veno-occlusive disease, and to develop methods of dose adjustment in order to optimize the use of this medication in children.Our work leaded to several methodological innovations, with the development and the validation of a non-parametric pharmacokinetic model for Bayesian dose adjustment of busulfan in pediatrics, and the development of a new method for the first dose determination maximizing the probability of achieving an exposure target range. From a clinical point a view, we highlighted the lack of clinical benefit in using an exposure target range narrower than those recommended. Furthermore, we identified that veno-occlusive incidence was correlated to the maximal concentration of busulfan, contrary to the area under the concentration-time curve.All of these results contribute to improving use and therapeutic monitoring of busulfan in pediatric onco-hematology

Afin d'analyser les données in vitro de l'effet de l'erlotinib sur la croissance des cellules A431 suivie par impédance-métrie, nous avons développé un modèle pharmacocinétique - pharmacodynamique non linéaire décrivant simultanément la diminution de la concentration d'erlotinib et son effet sur la croissance cellulaire au cours du temps. La non-linéarité du modèle imposant le recours à des méthodes itératives pour l'estimation des paramètres, plusieurs étapes de la procédure d'identification du modèle ont été étudiées et des solutions proposées, avec des exemples d'application à des molécules utilisées en oncologie:Choix du critère d'optimisation à employer - supériorité de la relation fonctionnelle de la moyenne géométrique pour l'identification de modèles non linéaires. Application données réelles: courbe de calibration d'une expérience de dosage ELISA du bevacizumab. Choix de l'algorithme d'optimisation le plus approprié au problème d'identification du processus pharmacocinétique. Les algorithmes dérivatifs sont les plus performants. Application données réelles: estimation simultanée des paramètres du modèle pharmacocinétique du 5-fluorouracile et de son métabolite principal.Transformation de la forme différentielle initiale du modèle en temps continu vers un modèle récursif en temps discret. Par ce moyen le modèle devient linéaire en ses paramètres, ce qui permet d'estimer directement les paramètres sans utiliser d'algorithme d'optimisation. Il devient également possible de suivre les variations des paramètres au cours du temps. Application données réelles: pharmacocinétique de la fotemustine, de la mitoxantrone et du 5-fluorouracile. / A nonlinear pharmacokinetic-pharmacodynamic model has been devised do simultaneously describe the loss of erlotinib and its effect on the cell growth over time, in order to analyze impedance-based data of erlotinib effect on A431 cells growth in vitro over time. The model non-linearity requiring the use of iterative methods for parameter estimation, several steps of the model identification were studied, and solutions proposed, with application examples to cancer drugs :Choice of the optimization criterion - superiotity of the geometric mean functionnal relationship for non-linear model identification. Real data application : calibration curve of a bevacizumab ELISA quantification experiment.Choice of the most appropriate algorithm for the pharmacokinetic process identification problem. The derivative algorithms perform better. Real data application : simultaneous identification of the 5-fluorouracil and of its main metabolite pharmacokinetic system.Transform of the differential initial continuous-time model in a recursive discrete time model. The transformed model becomes linear with respect to its parameters, allowing straightforward parameter estimation without using any optimization algorithm. It is then also possible to track the parameter variations over time. Real data application : pharmacokinetic model parameter estimation of fotemustine, mitoxantrone and 5-fluorouracil.

Free analyte is measured to be able to understand the pharmacological effects of a drug in the body, the binding to its ligand, and the effective drug level among other things. Thereby, it is important with correct measurements of free analyte, although it is not that easy to achieve since overestimations can occur. In this project, several immunoassays were developed for the bioanalytical methods Gyrolab and ELISA to measure free analyte, where the biotherapeutics Avastin® and Lucentis®, and the ligand VEGF were used as analytes. One difference between the methods is the short contact time of just a few seconds for Gyrolab compared to the sample incubation time of a couple of hours for ELISA. One difference between the antibodies is that Lucentis is an affinity-matured Fab region, and therefore, has a stronger affinity to VEGF compared to Avastin. When free Avastin was measured, the difference was significant, with ELISA estimating higher concentrations compared to Gyrolab. However, this was not the case for all assays. In some cases, this was probably due to differences between the methods that could not be seen. Otherwise, the results with no difference between the methods, when measuring free analyte with Lucentis as the drug, were expected due to the stronger affinity and longer halftime of dissociation. However, the difference with the longer sample incubation time for ELISA compared to the short contact time for Gyrolab seems to influence the measurement of free analyte, depending on the affinity of the components being measured.

Le traitement par éfavirenz, un médicament antirétroviral, a été associé avec des changements de profil lipidique potentiellement défavorables. Ce travail a abordé la question de savoir si ces effets dépendent des concentrations plasmatiques d’éfavirenz et, dans ce cas, si sa posologie pourrait être optimisée sans perte d'efficacité.Un modèle de pharmacocinétique de population a été développé à partir de données d’enfants infectés par le VIH. La simulation d’une population normalisée sous éfavirenz aux posologies recommandées montre que 15 % des enfants auraient des concentrations insuffisantes 12 heures après la prise, ce qui serait associé à un risque de la réplication virale de 23 %.Pour décrire la relation entre taux plasmatiques d'éfavirenz et changements de taux de cholestérol, des modèles de pharmacocinétique-pharmacodynamique (PK-PD) de réponse indirecte ont été développés. Le modèle sélectionné prédit que les taux d’éfavirenz individuels sont associés à une augmentation des lipoprotéines de haute densité sur 5 ans, et des lipoprotéines de basse densité durant 4 mois avec un retour progressif aux valeurs de base.Pour évaluer l’impact des concentrations d'éfavirenz sur l'efficacité, un modèle dynamique PK-PD a décrit la relation entre ces concentrations et l’évolution de la charge virale VIH et du taux de CD4. Un score d’efficacité a été développé sur la base d’hypothèses pharmacodynamiques pour prédire le risque de la réplication virale.L’utilisation de l’éfavirenz aux posologiques recommandées par la Food and Drug Administration aux Etats-Unis semble assurer une efficacité optimale et des changements potentiellement favorables dans les fractions de cholestérol. / As other antiretroviral drugs, treatment with efavirenz has been associated with potentially unfavorable lipid profile changes in adults and in children. The thesis addressed the question of whether these changes depend on efavirenz plasma concentrations and if dose adjustments could be envisioned without loss of efficacy.To estimate individual efavirenz exposure over 24 hours, a population pharmacokinetic model was developed using data from HIV infected children. Simulations for a normalized population receiving efavirenz dosed according recommendations predicted that 15% of children would have insufficient mid dose concentrations, associated with a 23% risk of viral replication.To describe the relationship between efavirenz concentrations and cholesterol changes, population pharmacokinetic-pharmacodynamic (PK-PD) indirect response models were developed. The selected model predicted that individual efavirenz concentrations were associated with an increase in high-density lipoprotein concentrations over 5 years but with an increase in low-density lipoprotein concentrations only during the first 4 months of treatment followed by a gradual return to baseline.To study the importance of efavirenz concentrations with regard to efficacy, a PK-PD dynamics model was developed to describe the relationship between concentrations and HIV RNA load and CD4 cell count evolutions. A score was defined based on a pharmacodynamic hypothesis to predict the risk of viral replication.Using US Food and Drug Administration dosing recommendations in children ensure optimal efficacy and potentially favorable changes in cholesterol fractions.

Schizophrenia is a troubling and severe mental illness that is only incompletely treated by currently available drugs. New drug development is hindered by a scarcity of functionally relevant pharmacodynamic biomarkers that are translatable across preclinical and human subjects. Although psychosis is a major feature of schizophrenia, cognitive and negative symptoms determine the long-term functional outcomes for patients. Stimulus-evoked neural synchrony at gamma (~ 40 Hz) frequency plays an important role in the processing and integration of sensory information. Not surprisingly, schizophrenia patients show deficits in gamma oscillations. NMDA receptor (NMDAR) activation on fast-spiking parvalbumin-positive interneurons is deemed important for the generation of gamma oscillations. NMDA hypofunction has been proposed as an alternative hypothesis to the well-known dopamine dysregulation to explain the neurochemical abnormalities associated with schizophrenia. For this dissertation, we validated a preclinical model to pharmacologically probe NMDA-mediated gamma oscillations by further characterizing the auditory-steady state response (ASSR) in female Sprague Dawley rats. The ASSR is a measure of cortical neural synchrony evoked in response to periodic auditory stimuli. ASSR at 40 Hz is consistently disrupted in patients. First, we established the reliability of click train-evoked 40 Hz ASSR and tone-evoked gamma oscillations in 6 separate sessions, spread over a 3-week period. Then we established the sensitivity of these neural synchrony measures to acute NMDAR blockade using the high affinity NMDA channel blocker MK-801, using a repeated measures design. Next, we compared the reliability and sensitivity of the 40 Hz ASSR from two distinct recording sites. Results from this study showed that as compared to vertex, temporal recording showed a greater gamma synchrony. However, the temporal recording had poor test-retest reliability and lower sensitivity to MK-801-induced disruption. Lastly, we characterized the dose-response profiles of an NMDA co-agonist D-serine, an atypical (clozapine) and a typical (haloperidol) antipsychotic, on the 40 Hz ASSR. Results from these studies showed that only clozapine was effective in robustly augmenting 40 Hz ASSR. Furthermore, only clozapine pretreatment had partial protective effect against MK-801 induced ASSR disruption. Overall, this work establishes that vertex recorded 40 Hz ASSR is a reliable neural synchrony biomarker in female SD rats that is amenable for bidirectional pharmacodynamic modulation.

No description available.

Tuberculosis is an ancient infectious disease and a leading cause of death globally. Preclinical research is important for defining drugs and regimens which should be carried forward to human studies. This thesis aims to characterize the population pharmacokinetics and exposure-response relationships of anti-tubercular drugs alone and in combinations, and to suggest experimental designs for preclinical settings. The population pharmacokinetics of rifampicin, isoniazid, ethambutol and pyrazinamide were described for the first time in two mouse models. This allowed for linking the population pharmacokinetic model to the Multistate Tuberculosis Pharmacometric (MTP) model for biomarker response, which was used to characterize exposure-response relationships in monotherapy. Pharmacodynamic interactions in combination therapies were quantitatively described by linking the MTP model to the General Pharmacodynamic Interaction (GPDI) model, which provided estimates of single drug effects together with a quantitative model-based evaluation framework for evaluation of pharmacodynamic interactions among drugs in combinations. Synergism (more than expected additivity) was characterized between rifampicin and ethambutol, while antagonism (less than expected additivity) was characterized between rifampicin and isoniazid in combination therapies. The new single-dose pharmacokinetic design with enrichened individual sampling was more informative than the original design, in which only one sample was taken from each mouse in the pharmacokinetic studies. The new oral zipper design allows for informative pharmacokinetic sampling in a multiple-dose administration scenario for characterizing pharmacokinetic-pharmacodynamic relationships, with similar or lower bias and imprecision in parameter estimates and with a decreased total number of animals required by up to 7-fold compared to the original design. The optimized design for assessing pharmacodynamic interactions in the combination therapies, which was based on EC20, EC50 and EC80 of the single drug, provided lower bias and imprecision than a conventional reduced four-by-four microdilution checkerboard design at the same total number of samples required, which followed the 3Rs of animal welfare. In summary, in this thesis the population pharmacokinetic-pharmacodynamic models of first-line drugs in mice were characterized through linking each population pharmacokinetic model to the MTP model. Pharmacodynamic interactions were quantitatively illustrated by the MTP-GPDI model. Lastly, experimental designs were optimized and recommended to both pharmacokinetic and pharmacodynamic studies for preclinical settings.

L’immunosuppression optimale après greffe d’organe solide est une balance délicate et propre à chaque individu entre le risque de rejet et les risques liés à une surexposition au traitement immunosuppresseur. L’évaluation de la fonction résiduelle des lymphocytes T après stimulation par un mitogène (pharmacodynamie effective) devrait permettre de mesurer l’effet direct des médicaments immunosuppresseurs sur leur cible. Nous avons étudié différents paramètres de pharmacodynamie effective chez 34 receveurs pédiatriques de greffe d’organes solides traités par tacrolimus et mycophénolate. Les tests proposés dans ce travail sont adaptés au milieu pédiatrique et à une réalisation en temps réel. La quantification du CD25 parmi les CD4 activés par l’OKT3 permet de distinguer deux groupes de patients selon leur degré d’immunosuppression. L’âge médian est plus bas et la concentration plasmatique médiane en MPA plus élevée dans le groupe de patients plus fortement immunosupprimés. L’étude des paramètres immunologiques pouvant influencer la réponse (sécrétion des interleukines, proportion des sous-populations lymphocytaires CD4, CD8, T naïfs et Trég) ainsi que l’étude du pouvoir de restauration de la fonction lymphocytaire par l’Il-2, la guanosine ou la xanthosine, ne permettent pas de mieux comprendre les variabilités interindividuelles observées. Ces résultats devront être confirmés sur une cohorte plus grande de patients afin de juger de leur intérêt en pratique clinique. / Optimal immunosuppression following solid organ transplantation is unique to each individual and requires a balance between risks of rejection and overexposure to immunosuppressive therapy. The evaluation of residual function of T lymphocytes after mitogen stimulation (effective pharmacodynamic monitoring) should allow measurement of the direct effect of immunosuppressive drugs on their target. We studied various parameters of effective pharmacodynamic monitoring in 34 paediatric patients receiving solid organ transplants and treated with tacrolimus and mycophenolate (MPA). The tests proposed in this work are adapted to the paediatric setting in real time. Quantification of CD25 among CD4 cells activated by OKT3 can differentiate two groups of patients according to their degree of immunosuppression. Median values for age and MPA plasma concentration are lower and higher, respectively, in the patient group most heavily immunosuppressed. Neither study of the parameters that may influence the response (secretion of interleukins, proportion of lymphocyte subpopulations CD4, CD8, naive and regulatory T cells) nor study of the restoration of basal cell function brought about by Il2, guanosine or xanthosine, helped to explain the observed inter-individual variability. These results should be confirmed in a larger cohort of patients in order to test their relevance in clinical practice.

With approximately nine million new cases and the attributable cause of death of an estimated two millions people every year there is an urgent need for new and effective drugs and treatment regimens targeting tuberculosis. The tuberculosis drug development pathway is however not ideal, containing non-predictive model systems and unanswered questions that may increase the risk of failure during late-phase drug development. The aim of this thesis was hence to develop pharmacometric tools in order to optimize the development of new anti-tuberculosis drugs and treatment regimens. The General Pulmonary Distribution model was developed allowing for prediction of both rate and extent of distribution from plasma to pulmonary tissue. A distribution characterization that is of high importance as most current used anti-tuberculosis drugs were introduced into clinical use without considering the pharmacokinetic properties influencing drug distribution to the site of action. The developed optimized bronchoalveolar lavage sampling design provides a simplistic but informative approach to gathering of the data needed to allow for a model based characterization of both rate and extent of pulmonary distribution using as little as one sample per subject. The developed Multistate Tuberculosis Pharmacometric model provides predictions over time for a fast-, slow- and non-multiplying bacterial state with and without drug effect. The Multistate Tuberculosis Pharmacometric model was further used to quantify the in vitro growth of different strains of Mycobacterium tuberculosis and the exposure-response relationships of three first line anti-tuberculosis drugs. The General Pharmacodynamic Interaction model was successfully used to characterize the pharmacodynamic interactions of three first line anti-tuberculosis drugs, showing the possibility of distinguishing drug A’s interaction with drug B from drug B’s interaction with drug A. The successful separation of all three drugs effect on each other is a necessity for future work focusing on optimizing the selection of anti-tuberculosis combination regimens. With a focus on pharmacokinetics and pharmacodynamics, the work included in this thesis provides multiple new methods and approaches that individually, but maybe more important the combination of, has the potential to inform development of new but also to provide additional information of the existing anti-tuberculosis drugs and drug regimen.

The thrust of this thesis is to study oral solid dosage formulation using hot melt coating method and to use pharmacokinetic modeling and simulation (PK M&S) as a tool that can help to predict pharmacokinetics of a drug in human and the probability of passing various bioequivalence criteria of the formulation based on the PK of the drug. Hot-melt coating using a new method, direct blending, was performed to create immediate and sustained release formulations (IR and SR). This new method was introduced to offer another choice to produce IR and SR drug delivery formulations using single and double coating layer of waxes onto sugar beads and/or drug loaded pellets. Twelve waxes were applied to coat sugar cores. The harder the wax the slower the drug was released from single coated beads. The wax coating can be deposited up to 28% of the weight of the core bead with 58% drug loading efficiency in the coating The cores were coated with single or double wax layers containing acetaminophen. Carnauba wax coated beads dissolved in approximately 6 hrs releasing 80% of loaded drug. However, when covered with another layer, the drug loaded beads released drug for over 20 hrs. When drug loaded pellets were used as cores, 33-58% drug loading was achieved. Double coated pellets exhibited a near zero order drug release for up to 16 hrs. Hot melt coating by direct blending using waxes is a simple process compared to conventional hot melt coating using coating pan or fluid bed coating machines. It offers an alternative way of making immediate, sustained drug release (IR, SR) and modified release (IR+SR) oral dosage forms of drugs which are stable at high temperature (100°C). The pellet-containing-drug coated formulations provide options when higher drug loading is warranted. It is required by the US Food and Drug Administration (FDA) that a new modified –release (MR) product or identical generic product be regarded as bioequivalent (BE) to the originators reference drug product. However, there are concerns that current regulatory criteria are not sufficient when evaluating bioequivalence (BE) for many MR products, and additional metrics for BE assessment of the products should be applied to ensure therapeutic equivalence. This study used pharmacokinetic modeling and simulation (M&S) to investigate 1) the probability of BE occurring between the MR test and reference products 2) the rates of false positive and true negative of the BE test; and 3) the estimation of the sample size in pivotal BE studies; all of which when partial area under the curves (pAUCs) were applied as additional BE criteria. Reference data of two MR forms of methylphenydate HCl (MPH) were simulated and obtained from literature (formulation Q and Metadate CD, respectively). Monte Carlo simulations were performed to simulate the test drug concentration profiles and BE assessment was carried out utilizing the mean (method 1) and individual concentration time curves (method 2). For formulation Q, adding pAUC₀₋[subscript Tmax] to current BE criteria reduced the possibility of passing BE from approximately 98% to 85%, with a true negative rate of 5%. The earlier the time points used to determine for pAUC before Tmax, the lower the chance of passing BE for the test product. The possibility of passing BE varied and depended on the coefficient of variations (CV) of T[subscript lag], K[subscript a] and K[subscript e] and that considerable variability in the parameters affected the earlier segments of the drug concentration profile curves more. Similar drug concentration time profiles between the test and reference products is recommended to ensure bioequivalence occurs with a reasonable subject sample size. A similar scenario was seen when Metadate CD was used as the reference product. PK M&S can help provide appropriate additional metrics to assure the BE test is a better tool ensuring therapeutic equivalence for MR products with little negative impact to generic manufacturers. Predictions can also be made about the required sample size and the chances of passing BE with any addition to the conventional three criteria for the test product. PK M&S was also used to predict drug concentrations of levofloxacin in tissue. Levofloxacin has been widely used in clinical practice as an effective broad-spectrum antimicrobial, however tendonitis and tendon rupture have been reported with increasing use of this agent. Here, these incidents will be assessed by investigating pharmacokinetic behavior of the compound to see if they are related to drug's tissue disposition. The PK model for levofloxacin was established. Mean concentration time profiles of single or multiple dosing of 500 mg levofloxacin following oral and IV infusion administration were simulated. Monte Carlo simulation was used to simulate the drug concentration time profiles in plasma (compartment 1) and tissue (compartment 2) after seven dosing regimens while varying the drug's elimination and distribution rates to see the effect of changing those rates have on the drug accumulation in tissue. Monte Carlo Simulation shows that low elimination rates affect the drug concentration in plasma and tissue significantly with the level in plasma rising up to 35 μg/mL at day 7. A normal elimination rate together with escalation of distribution rates from plasma to tissue could increase the tissue concentration after 7 doses to 9.5 µg/mL, a value that is more than twice that of normal. PK M&S can be used as an effective tool to evaluate drug concentration in different compartments (plasma and tissues, for example). The unexpectedly high concentration values in some cases may explain, at least in part, the reason of tendinopathy occurs in the clinical setting. / Graduation date: 2012 / Access restricted to the OSU Community at author's request from June 7, 2012 - June 7, 2014