This thesis covers a variety of topics around the central theme of pharmacological research involving children, with a specific focus on the development of minimally invasive methodology that can... Show moreThis thesis covers a variety of topics around the central theme of pharmacological research involving children, with a specific focus on the development of minimally invasive methodology that can be employed in future studies involving children. Children form a unique group within the area of pharmacological research and pharmacotherapy. The heterogeneity even within this group is large, covering the range of preterm neonates weighing 500 grams up to adolescents. Obviously, therapeutic needs change across this range, as among others disease epidemiology, drug disposition, pharmacodynamic response, and suitable drug formulations change with age. The same holds true for the design of drug trials involving children: where pharmacokinetics in adults can be studied simply by recruiting a number of healthy volunteers, such a study with a number of healthy toddlers is clearly not feasible and not acceptable. Therefore, approaches and new methodology are needed to circumvent these issues. Show less
For mechanism-based investigations on PK-PD relationships following intranasal administration, the use of advanced animal models and analytical techniques are crucial. As described in this thesis,... Show moreFor mechanism-based investigations on PK-PD relationships following intranasal administration, the use of advanced animal models and analytical techniques are crucial. As described in this thesis, quantitative information on distinction between extent as well as rate of absorption between nose-to-systemic and nose-to-brain distribution can now be obtained. Using plasma prolactin concentrations as a biomarker for dopamine D2 inhibition, a mechanism-based PK-PD model was developed. Most important aspects in this approach were incorporation of target site exposure (brain extracellular fluid) of remoxipride and a biological system response (positive feedback) mechanism on the synthesis of prolactin, thereby increasing the mechanistic insight in modulation of the dopaminergic system in rats. Simulating remoxipride brain extracellular fluid concentrations in humans, allometric scaling and use of independent information on interspecies differences proved that the structural model is applicable in both rats and man. Show less
Calcineurin inhibitors are crucial in the prevention of acute rejection in the first year after renal transplantation. Unfortunately, these drugs (ciclosporin A, tacrolimus) are characterized by... Show moreCalcineurin inhibitors are crucial in the prevention of acute rejection in the first year after renal transplantation. Unfortunately, these drugs (ciclosporin A, tacrolimus) are characterized by serious clinical toxicity and between patient variability in their effect. Therefore, the dose of these drugs should be individualized in order to reach a balance between rejection and toxicity. This thesis aimed to describe the variability between and within patients using mathematical models and subsequently to explain this variability. Genetic and non-genetic factors were used to explain variability and several factors were identified (polymorphism in metabolism enzyme CYP3A5, body weight, concomitant prednisolone dose). For this purpose drug concentrations in blood are measured as a concentration biomarker. Furthermore, another biomarker the activity ot the target enzyme calcineurin was determined in leukocytes, but was found to be more variable within patients than between patients. This response biomarker was not found to be clinically useful to individualize the drug dosage. Finally, pharmacological determinants for subclinical acute rejection at 6 months were determined in patients treated with ciclosporin. Although ciclosporin exposure and several genetic variants were not found to relate, a previous acute rejection period and a kidney from a deceased donor increased the risk of rejection 5-fold. Show less
Dahan, A.; Olofsen, E.; Sigtermans, M.; Noppers, I.; Niesters, M.; Aarts, L.; ... ; Sarton, E. 2011
Protein binding can have major impact on a drug__s pharmacokinetics (PK) and pharmacodynamics (PD). At present the theoretical basis of the influence of (alterations in) plasma protein binding on... Show moreProtein binding can have major impact on a drug__s pharmacokinetics (PK) and pharmacodynamics (PD). At present the theoretical basis of the influence of (alterations in) plasma protein binding on pharmacokinetics is well-established. The role of plasma-protein binding on pharmacodynamics however has sofar not been established in a systematic manner. As such there is no scientific basis for the __free drug hypothesis__ which states that the pharmacological activity is correlated with unbound drug concentrations in plasma. The objective of the research described in this thesis is to determine, in a strictly quantitative manner, the influence of plasma protein binding on in vivo pharmacodynamics. To this end both in silico and in vivo investigations were performed using the beta-blockers as model compounds. In contrast to the PK, the free drug concentration is the main determinant of the PD under equilibrium conditions for both target and plasma protein. Moreover for the beta-blockers, the free plasma concentration appears to be the best predictor of in vivo PD. In case of a dynamic interaction, the probability of non-restrictive protein binding is (theoretically) higher with regard to the PD under certain conditions, but more extensive research is needed to confirm this statement. Show less
This thesis describes different ways of exploring the pharmacological and therapeutic effects of novel GABA-ergic and GABA-like agents in humans. Systematic pharmacodynamic evaluations, using well... Show moreThis thesis describes different ways of exploring the pharmacological and therapeutic effects of novel GABA-ergic and GABA-like agents in humans. Systematic pharmacodynamic evaluations, using well-characterised positive controls, can confirm or refute the unique pharmacological properties of GABAA-subtype selective drugs in healthy volunteers. Such studies can help to predict dosing regimens and therapeutic advantages of these drugs. The distribution of different GABAA-receptor subtypes provides clues for their functional relevance. This knowledge can be used to optimise the desirable and undesirable effect profiles of selective GABA-ergic drugs. Very little is still known about the pathophysiological relevance of GABA-systems in CNS-disorders, although GABA-ergic treatments are in use for a wide range of clinical conditions. The availability of novel compounds with well defined pharmacological characteristics can clarify the involvement of these mechanisms in normal or abnormal physiology. This thesis hopes to show that carefully designed studies, using a range of CNS-measurement that reflect different GABAergic systems, can aid in the development of new GABA-ergic drugs, and help to unravel the role of the different GABA-ergic systems in health and disease. Show less
Although cannabis is especially known for its recreational use as a __soft drug__, its potential therapeutic properties have been recognized for hundreds of years. Since the isolation of THC from... Show moreAlthough cannabis is especially known for its recreational use as a __soft drug__, its potential therapeutic properties have been recognized for hundreds of years. Since the isolation of THC from Cannabis sativa L, the discovery of cannabinoid receptors and their natural ligands (endocannabinoids) the interest in the development of novel cannabinoids as medicine is accelerating. This thesis describes useful cannabis-biomarkers and the clinical pharmacology of some cannabinoid agonists and antagonists in early phase drug development. This includes a novel mode of pure intrapulmonary THC administration that can be used as a benchmark for novel CB1/CB2-agonists, or to demonstrate inhibitory activity of CB1-antagonists. In addition, the pharmacodynamics and pharmacokinetics of two novel CB1/CB2 agonists are evaluated and compared with the pharmacodynamic effect profile of THC. The clinical trials carried out for this research were performed at the Centre for Human Drug Research, Leiden, The Netherlands. Show less
The overall goal was to develop individualized dosing guidelines for the sedatives propofol and midazolam in infants and in critically ill patients, on the basis of population pharmacokinetic... Show moreThe overall goal was to develop individualized dosing guidelines for the sedatives propofol and midazolam in infants and in critically ill patients, on the basis of population pharmacokinetic-pharmacodynamic (PK-PD) modeling. Both under- and oversedation significantly and adversely affects patient outcome. Due to the high intra- and interindividual variability in dose requirements dosing is complicated. In this thesis the interindividual variability in response has been examined by covariate analysis. In this analysis the effects of bodyweight, cardiac function, severity of illness and liver blood flow and the unexplained interindividual variability have been characterized. It was shown that infants require higher doses of propofol because of differences in pharmacokinetics rather than pharmacodynamics. When comparing the results of the PK-PD model of propofol and midazolam in infants, propofol is preferred over midazolam because of the lower interindividual variability in pharmacodynamics compared to midazolam. In critically ill patients severity of the illness was found to be a major determinant of the level of sedation, with lower propofol dosing requirements with increasing severity of illness. The PK-PD models can be used as a basis for individualized dosing of propofol and midazolam, which is essential for optimizing the quality of sedation in clinical practice and will improve patients__ outcome. Show less
