Prematurely born neonates require, amongst others, pharmaceutical therapy. Dosing guidelines for these therapies are often based on data from term born neonates or older infants, while these are... Show morePrematurely born neonates require, amongst others, pharmaceutical therapy. Dosing guidelines for these therapies are often based on data from term born neonates or older infants, while these are not necessarily similar to prematurely born neonates. When suboptimal dosing guidelines are applied the neonates are at risk for under- or overdosing. In this thesis the pharmacokinetics and pharmacodynamics of a variety of drugs frequently used in preterm neonates were characterized, ultimately to optimize treatment. Specifically, caffeine, ibuprofen and fluconazole were studied which are drugs to treat apnea of prematurity, to close a patent ductus arteriosus and to treat or prevent infections with Candida in newborns, respectively. These drugs were introduced and used in clinical practice without sufficient knowledge, especially on appropriate dosing for this subpopulation. For caffeine and ibuprofen we found that the clearance rapidly increases with postnatal age, while for fluconazole clearance is better reflected by body weight and serum creatinine. For these drugs dosing guidelines were proposed based on identified covariates for their pharmacokinetics. Ibuprofen therapy was further investigated by examining the course of spontaneous closure of the ductus arteriosus, and evaluating the effects of ibuprofen exposure and patient characteristics simultaneously. Show less
Fungal infections pose a significant threat to individuals with compromised immune systems and despite advancements in diagnosis and treatment, they continue to jeopardize patient’s health.... Show moreFungal infections pose a significant threat to individuals with compromised immune systems and despite advancements in diagnosis and treatment, they continue to jeopardize patient’s health. Maximizing the effectiveness of existing antifungal drugs is imperative. Among these, fluconazole and posaconazole are commonly prescribed to treat severe and life-threatening fungal infections. In this thesis, among others, we aimed to understand better how well different posaconazole formulations are absorbed. Through computational modeling and simulation, we learned that posaconazole is best taken with food to reduce the risk of inadequate drug absorption and subsequent therapeutic failure. This applies not only to the suspension but also to the tablet, which results in higher and more predictable absorption even though it does not achieve concentrations similar to those upon intravenous administration. Fluconazole was studied in individuals with obesity. Our findings indicate that heavier adult males may require a higher dose to achieve the desired exposure. Consequently, we proposed dosing recommendations for treating obese patients. In summary, this research, a result of the long-term collaboration between Leiden University and Radboudumc, enhanced our knowledge of factors that reduce exposure to antifungal drugs, allowing us to guide how to individualize and optimize antifungal treatment in individual patients. Show less
Sepsis is a life-threatening condition caused by a dysregulated host response to infection, it is associated with significant morbidity, mortality, and with a high financial burden on global... Show moreSepsis is a life-threatening condition caused by a dysregulated host response to infection, it is associated with significant morbidity, mortality, and with a high financial burden on global healthcare systems. Bacterial infections are the primary cause of sepsis, but the growing prevalence of antimicrobial resistance complicates the effectiveness of antimicrobial treatments. Moreover, limited understanding of the host immune response during sepsis hinders the discovery of valuable biomarkers and drug targets. As such, there is an urgent need to improve the treatment of sepsis. To tackle this challenge, we have concentrated our efforts on optimizing current treatment strategies and on facilitating the discovery of novel host inflammatory response directed therapeutics. In this thesis, we have utilized quantitative pharmacological modeling approaches to assess the adequacy of current dose regimens and to evaluate antibiotic pharmacokinetic variability, thereby optimizing antimicrobial therapies for sepsis. Additionally, our researches had aimed to deepen our understanding of the underlying dynamics of sepsis pathology, enabling the identification of promising biomarkers and therapeutic targets for sepsis. Our work demonstrated how quantitative modeling strategies can support the design of optimized treatment strategies, and how systematic model-based integration of disease mechanisms can help to overcome the translational challenges in sepsis drug development. Show less
Treosulfan-based conditioning has gained popularity in pediatric allogeneic hematopoietic stem cell transplantation (HSCT) because of its presumed favourable efficacy and toxicity profile.... Show moreTreosulfan-based conditioning has gained popularity in pediatric allogeneic hematopoietic stem cell transplantation (HSCT) because of its presumed favourable efficacy and toxicity profile. Treosulfan is used in standardized dosing regimens based on body surface area. The relationship between systemic treosulfan exposure, early and long term clinical outcome in pediatric patients undergoing allogeneic hematopoietic stem cell transplantation (HSCT) for non-malignant diseases is unresolved. In this thesis we aimed to answer these questions. We found a relationship between the level of exposure to treosulfan and acute toxicity, but we found no relationship with the risk of rejection, survival and long-term endocrine complications. A personalized dose of treosulfan can therefore be useful to reduce toxicity in children, but because the toxicity profile of treosulfan is generally relatively mild, it will not be necessary in most cases. This is beneficial, because measuring blood levels is not always available in every hospital. Future research should focus on specific disease categories or patient groups that may benefit from treosulfan monitoring. More research is also needed on the late complications of treosulfan, such as dental, neurocognitive, hair, eye and lung problems, as this aspect becomes increasingly important as more (very young) patients undergo stem cell transplantation. Show less
Primary endpoints in pediatric clinical trials are currently very similar to those in adult trials1, and focus on quantifying or counting hard endpoints like mortality, hospital admissions and... Show morePrimary endpoints in pediatric clinical trials are currently very similar to those in adult trials1, and focus on quantifying or counting hard endpoints like mortality, hospital admissions and length of stay. Additionally, biochemical biomarkers in serum are often measured to assess drug effects on a biochemical level. The occurrence of mortality and hospital admissions is rare thanks to the improvements in clinical care that have occurred in the last century, and adopting these as primary endpoints in clinical trials gives disproportional weight to rare events which most patients will not experience. Conversely, length of stay for many clinical conditions is short, and this duration only captures a small part of the clinical recovery trajectory that patients must undergo. This dissertation described the development, technical validation and clinical validation of a new type of clinical endpoints ('value based endpoints') and a new clinical trial paradigm (The remote clinical trial), consisting of digital endpoints and non-invasive pharmacokinetic sampling. Both have the potential to transform pediatric clinical trials and pediatric clinical care. The process towards implementation is challenging and can only proceed after a rigorous validation process. The current work provides a roadmap towards selection, validation, and implementation of digital endpoints, and describes preliminary steps taken for several candidates. The digital endpoints investigated in this work fulfill several validation criteria in a range of clinical conditions and, combined with non-invasive pharmacokinetics, may move the pediatric clinical trial completely towards the home. Show less
The last decades it is increasingly recognized that acute as well as chronic postoperative pain is an important problem. Treatment and prevention of postoperative pain is a challenge, especially in... Show moreThe last decades it is increasingly recognized that acute as well as chronic postoperative pain is an important problem. Treatment and prevention of postoperative pain is a challenge, especially in special patient populations where there is only limited guidance on how to optimally use opioids. In this thesis we focused on the perioperative use of opioids in three different populations. First, the influence of the opioids remifentanil versus fentanyl on acute and chronic postoperative pain was investigated in adult cardiac surgery patients. Second, pharmacodynamic modelling methods were applied to analyze the postoperative use of morphine in children after cardiac surgery. Finally, a pharmacokinetic model was developed to investigate the influence of obesity on the pharmacokinetics of morphine and its metabolites. Pain remains a complex puzzle among biological, psychological, behavioral and social-cultural factors. The high inter-individual variation in all of these factors results in postoperative pain still being a major issue while the ultimate goal is to stay without pain after a surgical procedure. Therefore, the answer to the question: “Does it still hurt?” is: YES unfortunately. This thesis adds pieces to this complex puzzle by focusing on the use of opioids in three different patient populations. Show less
Although ketamine can be considered to be an “old” drug, a definitive model explainingketamine pharmacokinetics for a wide range of patient populations, dosing regimens and ketamine administrations... Show moreAlthough ketamine can be considered to be an “old” drug, a definitive model explainingketamine pharmacokinetics for a wide range of patient populations, dosing regimens and ketamine administrations forms is lacking. Currently, a large number of ketamine population pharmacokinetic models is published. However, the large number of ketamine pharmacokinetic models based on data from all types of study populations,ketamine dosing regimens and administration forms, can prove to become a serious challenge for clinical decision makers, since it may not always be easy to pick the model that best suits their patient population. In this thesis, we focus on unraveling the complex pharmacokinetics and pharmacodynamics that characterize ketamine, in order to get a step closer to a final “all encompassing” pharmacokinetic-pharmacodynamic model. For the pharmacodynamic outcomes, we especially focus on the effects of ketamine on neuropathic pain, nociceptive pain (pressure pain) and psychedelic outcomes. Show less
The prevalence of obesity (BMI >40 kg/m2) has increased rapidly over the recent years, not only in adults, but also in children and adolescents. Although it is well known that (patho... Show moreThe prevalence of obesity (BMI >40 kg/m2) has increased rapidly over the recent years, not only in adults, but also in children and adolescents. Although it is well known that (patho)physiological changes in obese individuals can influence drug pharmacokinetics, implying adjusted doses, there is still a need for specific dose guidelines for many classes of drugs. In this thesis, the pharmacokinetics of the renally cleared antibiotics gentamicin, tobramycin and vancomycin, drugs for which it is well known that both the efficacy and toxicity of these drugs closely relate to blood concentrations, are studied in non-obese and (morbidly) obese adults, adolescents and children. We present practical dose recommendations for the obese adult, paediatric and adolescent populations. Furthermore, some important questions are addressed regarding the pharmacokinetics of drugs in obesity: can we use the lipophilicity of a drug to predict changes in volume of distribution? Which pitfalls have to be considered when using lean body weight as basis for drug dosing? And which methods for estimating glomerular filtration can predict the clearance of renally cleared drugs in obese patients? The work in this thesis provide some important steps in filling the current knowledge gaps regarding the pharmacokinetics of drugs in obesity. Show less
The aim of this thesis was to stimulate rational and effective use of antimicrobials, by addressing the first two cornerstones: (1) refining stewardship of existing antimicrobials and (2) re... Show moreThe aim of this thesis was to stimulate rational and effective use of antimicrobials, by addressing the first two cornerstones: (1) refining stewardship of existing antimicrobials and (2) re-introducing old antibiotics within the framework of antimicrobial stewardship. The overall aim is to contribute to antimicrobial stewardship and to explore the value of the re-introduction of old antibiotics that are currently scarcely used. The basic step is the in vitro relationship expressed as minimal inhibitory concentration (MIC) for a given bacteria for a given antibiotic. The next step is the in vivo situation. This thesis concentrates on the in vivo situation. Show less
A novel mathematical model describes spatial-temporal drug distribution within one or more brain units, which are cubic representations of a piece of brain tissue with brain capillaries at the... Show moreA novel mathematical model describes spatial-temporal drug distribution within one or more brain units, which are cubic representations of a piece of brain tissue with brain capillaries at the edges. The brain unit can be considered a highly representative building block of the brain in terms of drug distribution. While the focus of the model is on drug distribution within the brain ECF, the model includes descriptions of drug concentrations within the blood plasma, drug distribution via brain capillary blood flow, drug transport across the blood-brain barrier (BBB) by passive paracellular and transcellular transport as well as active transport, brain ECF diffusion, brain ECF bulk flow, non-specific binding of the drug to brain tissue, and drug target binding kinetics. We study the model with analytical methods and numerical simulations. This allows us to examine the integrated effect of the individual processes important to drug distribution and effect on the local concentration-time profiles of free and (non-)specifically bound drug. Moreover, the model allows us to generate a local distribution profile of a drug within the brain. In addition, the impact of disease-induced changes in brain-specific properties on the concentrations of drug within the brain ECF is assessed. Show less
The aim of this thesis is to expedite and ensure the systematic accuracy of clearance scaling from adults to paediatric patients, with a special focus on drugs undergoing hepatic metabolism. A... Show moreThe aim of this thesis is to expedite and ensure the systematic accuracy of clearance scaling from adults to paediatric patients, with a special focus on drugs undergoing hepatic metabolism. A physiologically-based pharmacokinetic simulation workflow was developed to unravel the conditions for accurate scaling of drug clearance from adults to children as young as term neonates of one day for various methods. This disproved the belief that a universal allometric exponent can scale size-related changes in clearance across the paediatric age range, and showed that isoenzyme maturation and drug properties, especially extraction ratio and drug binding to alpha-1-acid glycoprotein, should be accounted for when scaling clearance to young children. Based on these results, a clearance scaling decision tree is proposed, which allows pharmacologists for the first-time to select scaling method(s) that require a minimum but still sufficient amount of information to accurately scale clearance of drugs with known properties to a desired paediatric age-range. Moreover, an analysis framework is provided to assess the feasibility and clinical trial requirements for the estimation of PBPK parameters using population pharmacokinetic modelling, which has the potential to expedite development of PBPK models for understudied paediatric subpopulations. Show less
Growth and development affect the metabolism of drugs administered to neonates, infants, and children. Research in this thesis focused on the metabolism by cytochrome P450 (CYP) 3A enzymes, aiming... Show moreGrowth and development affect the metabolism of drugs administered to neonates, infants, and children. Research in this thesis focused on the metabolism by cytochrome P450 (CYP) 3A enzymes, aiming to predict CYP3A-mediated clearance in neonates, infants, and children, by development of pediatric (physiological) population pharmacokinetic models.CYP3A-mediated systemic metabolism of midazolam in critically ill pediatric patients was found to be impacted by body weight, critical illness, and inflammation. The developed model was subsequently found to accurately predict clearance in postoperative children or critically ill patients. Furthermore, advanced physiological modelling methods were applied to distinguish between first-pass and systemic CYP3A-mediated metabolism to elucidate the role of intestinal and hepatic CYP3A in neonates and children covering the whole pediatric age range. Lastly, it was described when a pediatric covariate function for CYP3A-mediated midazolam clearance could be applied to scale plasma clearance of other CYP3A substrates in the pediatric population.This work will significantly improve CYP3A-mediated clearance predictions in neonates, infants, and children, which will ultimately lead to rational support for pediatric doses of CYP3A substrates in first-in-child studies during drug development and for pediatric dose recommendations for CYP3A substrates in clinical practice. Show less
In this thesis we describe the latest developments in the field of advanced thyroid cancer. Several clinical trials with sorafenib and everolimus were performed. The relation between clinical... Show moreIn this thesis we describe the latest developments in the field of advanced thyroid cancer. Several clinical trials with sorafenib and everolimus were performed. The relation between clinical outcome and mutational status was analyzed. Furthermore, the pharmacokinetics of everolimus in patients with advanced thyroid cancer was described. Show less
Biopharmaceuticals are among the most celebrated drugs. However, despite decades of experience, our understanding of many in vivo pharmacokinetic and adverse effects of biopharmaceuticals is... Show moreBiopharmaceuticals are among the most celebrated drugs. However, despite decades of experience, our understanding of many in vivo pharmacokinetic and adverse effects of biopharmaceuticals is still limited. These include the delay in reaching the maximum plasma concentration for an intravenously administered therapeutical protein, and the highly variable plasma concentration during elimination of monoclonal antibodies. Both observations can be explained by dynamical binding (‘stickiness’) of proteins to various (bodily) surfaces. Biopharmaceuticals also frequently contain (non-human) impurities, some of which are harmful when administered (‘dirtiness’). This toxicity often is the result of an intricate interplay of multiple cell types and effector pathways which can be difficult to simulate in the laboratory. More sophisticated test platforms are available, which can detect a number of untoward reactions that would previously not have been discovered. However, no laboratory test is fail-safe, and awareness of the possibility of adverse immunostimulation caused by biopharmaceuticals is the most important aspect for early detection and prevention of such cases in the future. Show less
Sunitinib treatment requires a personalized approach, since patients can respond very differently to this drug. Pharmacogenetics may improve our ability to provide a tailored therapy by studying... Show moreSunitinib treatment requires a personalized approach, since patients can respond very differently to this drug. Pharmacogenetics may improve our ability to provide a tailored therapy by studying how genetic variations could influence drug response. The objective of this thesis was to find genetic markers that can predict toxicity and efficacy of sunitinib in patients with metastatic renal cell carcinoma. This research builds upon previous findings from candidate gene studies by testing a selection of SNPs based on plausible involvement in pharmacokinetics or pharmacodynamics of the drug of interest. We observed that SNPs located in genes involved in metabolism and drug absorption (CYP3A4, CYP3A5, and ABCB1) are potentially associated with the clearance of sunitinib and its active metabolite. In analogy to this, we confirmed SNP associations from previous studies for SNPs in CYP3A5 and ABCB1 that predict the need for dose reductions and improvement of PFS on sunitinib. Sunitinib-induced toxicity is possibly related to SNPs in CYP3A4 and CYP3A5, and in interleukin genes IL8 and IL13. VEGFR-2 (KDR) rs34231037 G-allele variant carriers were potentially associated with a favorable response to sunitinib. A GWAS learned us that SNPs in chromosome 21 are involved in sunitinib efficacy, probably by influencing drug resistance mechanisms. Show less
This thesis concerns five studies where the statistical consequences of violations of modeling assumptions are assessed using experimental and simulated pharmacokinetic-pharmacodynamic data. The... Show moreThis thesis concerns five studies where the statistical consequences of violations of modeling assumptions are assessed using experimental and simulated pharmacokinetic-pharmacodynamic data. The first study describes the development of an open source web application for Bland-Altman analysis of comparison data, which is able to take into account both intra- and interindividual variability. In the second study the behavior of Akaike's information theoretic criterion is investigated in the presence of interindividual variability. The effects of neglecting or allowing for process noise are described in the third and fourth studies, for surrogate measures of clinical endpoints such depth of anesthesia and analgesia. In the fifth study pharmacodynamic model parameter estimates are compared when these are based on venous versus arterial blood samples. Show less
Many physiological processes, including those involved in the absorption, distribution, metabolism, elimination, pharmacodynamics and toxicity of therapeutic drugs, show profound fluctuations... Show moreMany physiological processes, including those involved in the absorption, distribution, metabolism, elimination, pharmacodynamics and toxicity of therapeutic drugs, show profound fluctuations over the course of the day and night. This may lead to time-of-day dependent changes in the exposure and effect of therapeutic drugs. The aim of this thesis is to provide a structured framework for chronopharmacological studies, while concurrently touching upon several critical issues encountered during the development and optimization of new and existing drug treatments. Firstly, we studied 24-hour variation in the pharmacokinetics of both midazolam and levofloxacin in healthy male subjects and found that for both drugs, absorptive processes show time-of-day dependency. Moreover, the magnitude of QT prolongation induced by levofloxacin, a common side-effect induced by many types of drugs, varied considerably and systematically over the course of the day. Furthermore, we investigated daily variation of drug distribution to the brain and found that time of day can be a considerable source of variation that could influence the effectiveness of drugs targeted to the brain. Taken together, these studies show that chronopharmacological aspects should not be overlooked in order to benefit from the systematic fluctuations in physiological processes during the development and optimization of drug treatments. Show less
Despite the increasing number of obese patients, evidence-based dosing guidelines are scarce, particularly for obese children and morbidly obese adults (BMI > 40 kg/m2). For both these... Show more Despite the increasing number of obese patients, evidence-based dosing guidelines are scarce, particularly for obese children and morbidly obese adults (BMI > 40 kg/m2). For both these populations, pharmacokinetic studies are needed to provide a basis for evidence-based dosing guidelines. In this thesis, we studied the pharmacokinetics of the CYP3A substrate midazolam, the renally excreted drug metformin and acetaminophen (metabolized by glucuronidation, sulphation and CYP2E1) in obese adolescents and/or morbidly obese adults. We address several currently unanswered questions; Can doses for obese adolescents be predicted on the basis of data obtained in morbidly obese adults? How to analyse pharmacokinetic data in obese adolescents, for whom body weight is influenced by growth, age and obesity? How to achieve safe and effective acetaminophen dosing for morbidly obese patients? The studies described in this thesis contribute to the existing gaps in knowledge regarding the pharmacokinetics and evidence-based dosing of drugs in obese adolescents and morbidly obese adults. Show less
Both tyrosine kinase inhibitors (tki) and mammalian target of rapamycin (mTOR) inhibitors are oral targeted therapies that are used for the treatment of a variety of malignancies. Due to the... Show moreBoth tyrosine kinase inhibitors (tki) and mammalian target of rapamycin (mTOR) inhibitors are oral targeted therapies that are used for the treatment of a variety of malignancies. Due to the growing evidence for drug exposure-response relationships, in combination with their high interpatient variability in pharmacokinetics (pk) and a fixed dosing regimen, it is hypothesized that dose individualization of oral targeted therapies may lead to better treatment outcomes both in terms of efficacy as well as toxicity. This thesis describes the results of different studies that investigated dose optimization strategies of oral targeted therapies used in oncology, with a focus on the TKIs pazopanib and sunitinib and the mTOR inhibitor everolimus. Show less
This thesis focuses on the implications of empirical evidence generation for the evaluation of safety and toxicity during drug development. A shift in paradigm is proposed to 1) ensure that... Show moreThis thesis focuses on the implications of empirical evidence generation for the evaluation of safety and toxicity during drug development. A shift in paradigm is proposed to 1) ensure that pharmacological concepts are incorporated into the evaluation of safety and toxicity; 2) facilitate the integration of historical evidence and thereby the translation of findings across species; and 3) promote the use of experimental protocols tailored to address specific safety and toxicity questions. Nonlinear-mixed effects modelling is recommended as a tool to account for such requirements. Our goal was to explore the feasibility of a model-based approach to toxicology assessment and risk prediction in humans and, where possible, to compare the performance of this approach to traditional safety assessment approaches. The investigational plan of the thesis was divided into two sections where the development of methodology is followed by a case study with real data. A variety of analysis strategies and protocol designs are investigated where we set the constraint that proposals to deviate from existing protocols be minimal. We finally compile recommendations for protocol optimisation and data analysis/interpretation strategies to facilitate the implementation of model-based techniques in safety pharmacology and toxicology research Show less
